The C.D.C. examined data from four flu seasons and concluded that vaccine effectiveness can decline by as much as 6 to 11 percent per month. And a European study reported that effectiveness declined from 53 percent to 12 percent beginning three months after receipt of the 2011-12 flu vaccine.

But other studies found that immunity waned for some, but not all, strains of influenza, or that immunity waned only in children and adults 65 years of age and older. Some found no significant waning at all.

One explanation for such conflicting results is that many of these studies have been observational, which are inherently more susceptible to bias and hidden methodological problems that can skew results than randomized placebo-controlled trials.

An example of such skewing is the so-called “leaky vaccine effect.” Because unvaccinated individuals are vulnerable to flu, they tend to get sick early in the flu season. As a result, there is a greater proportion of people who have been vaccinated who are susceptible to getting sick late in the flu season. These and other factors can complicate the statistical models upon which these studies are based.

In weighing the evidence and its limitations, the best approach is to follow the recommendations of the C.D.C.: “Balancing considerations regarding the unpredictability of timing of onset of the influenza season and concerns that vaccine-induced immunity might wane over the course of a season, it is recommended that vaccination should be offered by the end of October.”

It seems like summer just ended, yet pharmacies and schools are already telling us to line up for our flu shots.

© Getty Doctor or nurse gives vaccine or medicine injection to adult Asian descent patient in office or clinic setting. She uses syringe and wears gloves. Medical exam, consultation, therapist.

But the Centers for Disease Control and Prevention (CDC) recommended today that people get their vaccines for the 2018-19 flu season by the end of October. In other words, two solid months from now.

The exact timing of flu season in the U.S. varies every year, but it’s typically in fullest frenzy in December, January, and February. That’s when you want to make sure you’re best protected. “We know that antibodies peak four to six weeks after getting a vaccine and then slowly go down over the next six months,” explains Ann Falsey, MD, professor of medicine in the infectious disease unit at the University of Rochester Medical Center. “There are some theoretical concerns toward spring that you might be less protected if you get vaccinated too early.”

© Provided by Meredith Corporation

RELATED: Here’s Where You Can Get a Free Flu Shot Right Now—With or Without Insurance

She advises her patients to get their flu shots in late September or early October–and definitely by Halloween–so they’re protected before flu activity peaks in those winter months.

You’ll have some measure of protection even earlier, as antibodies–proteins that develop in the blood as part of the immune system’s natural response to potentially harmful invaders like the influenza virus–initially kick in about two weeks after you’re vaccinated.

RELATED: Why You Should Get the Flu Shot Every Year

But timing of the flu season and, therefore, the vaccine, is just one question mark factoring into how effective any vaccine will be. The other is how well the flu strains in the vaccine match what’s actually circulating. And that’s always a bit of a guessing game.

The CDC recommends that all individuals age 6 months and older who don’t have a specific reason not to get vaccinated–like a history of allergic reactions to the flu shot–do so. It’s especially important in older adults, who tend to have more and worse complications from the flu, as well as in people who have certain chronic health conditions or who are pregnant.

In addition to pharmacies and schools, you can also get the flu vaccine at your doctor’s office, urgent-care clinics, and many workplaces for free.

Ultimately, there’s really no bad time to get vaccinated. You might be a little late, but do it anyway.

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Contents

Is it too early to get a flu shot?

TAMPA, Fla. — You may have already seen the signs at your local pharmacy saying that flu shots are available and you’ve thought to yourself, “It’s way too early for that!”. You’d be wrong.

Nancy Epps, R.N., B.S.N. at Tampa General Hospital is better known as a flu shot expert. She says September is the ideal time to get a flu shot because you want to be protected before everyone around you is getting sick. By then it may just be too late.

In Florida, peak flu season is actually January through February where as it usually peaks December nationwide. Epps says the antibodies you create after getting the flu vaccine protect you for about six months, so you’ll be covered before the spread of the flu and through peak season if you’re vaccinated in September.

“We get a lot of people that say ‘I’m a healthy individual, I don’t need the flu shot’ but you’re in contact with a lot of people it could really endanger and cause them a lot of complications,” says Epps. She recommends the shot based off the CDC. Anyone older than six months should get the shot. People who are most at risk of getting the flu are between the ages of six months and 5 years old, over the age of 65, pregnant women and anyone with a pre-existing condition that lowers their immune system.

“Also remember, the flu vaccine is not 100 percent effective,” says Epps. She does say that even if you do get sick after getting the flu shot, having the vaccine will help decrease the effects of flu symptoms.

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Too Late for the Flu Vaccine?

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Flu season runs from October to May, with most cases happening from late December to early March. Getting vaccinated before the flu season is in full force (ideally by the end of October) gives the body a chance to make antibodies that protect from the virus.

Even though it’s best to get vaccinated as soon as the flu vaccine is available, getting the vaccine later still can be helpful. Even as late as January, there are still a few months left in the flu season, so it’s still a good idea to get protected.

Who Should Get the Flu Vaccine?

The flu vaccine is recommended for everyone age 6 months and older. It’s especially important for people who are at greater risk of having health problems from the flu to get vaccinated. They include:

  • all kids 6 months through 4 years old (babies younger than 6 months are also considered high risk, but they can’t get the flu vaccine)
  • anyone 65 years and older
  • all women who are pregnant, trying to become pregnant, have recently given birth, or are breastfeeding during flu season
  • anyone whose immune system is weak from medicines or illnesses (like HIV infection)
  • people who live in long-term care facilities, such as nursing homes
  • anyone (adults, teens, and kids) with an ongoing medical condition, such as asthma or diabetes
  • kids or teens who take aspirin regularly and are at risk for developing Reye syndrome if they get the flu
  • caregivers or household members of anyone in a high-risk group (like children younger than 5 years old, especially those younger than 6 months, and those with high-risk conditions)
  • Native Americans and Alaska Natives

Kids under 9 years old need two doses of flu vaccine if they’ve had fewer than two doses before July 2019. This includes kids who are getting the flu vaccine for the first time. Those under 9 who have received at least two doses of flu vaccine previously (in the same or different seasons) will only need one dose. Kids older than 9 only need one dose of the vaccine.

It can take up to 2 weeks for the flu vaccine to become effective, so it’s best to get vaccinated as soon as possible.

What Are the Types of Flu Vaccine?

Two types of flu vaccine are available for the 2019–2020 flu season. Both protect against four types of influenza virus:

  • the flu shot, which is injected with a needle
  • the nasal spray, a mist which gets sprayed into the nostrils

In the past, the nasal spray vaccine wasn’t recommended for kids because it didn’t seem to work well enough. The newer version appears to work as well as the shot. So either vaccine can be given this year, depending on the child’s age and general health.

The nasal spray is only for healthy people ages 2–49. People with weak immune systems or some health conditions (such as asthma) and pregnant women should not get the nasal spray vaccine.

Who Shouldn’t Get the Flu Vaccine?

Certain things might prevent a person from getting the vaccine. Talk to your doctor to see if the vaccine is still recommended if your child:

  • has ever had a severe allergic reaction to a flu vaccine
  • has had Guillain-Barré syndrome

Egg Allergy and the Flu Vaccine

In the past, people with an egg allergy had to check with their doctor about whether the flu vaccine was OK for them because it’s grown inside eggs. But health experts now say that the amount of egg protein in the vaccine is so tiny that it’s safe even for kids with a severe egg allergy. This is especially important during a severe flu season.

Still, a child with an egg allergy should get the flu vaccine in a doctor’s office, not at a supermarket, drugstore, or other venue.

If your child is sick and has a fever, or is wheezing, talk to your doctor about whether to reschedule the vaccine.

Are There Side Effects?

Most people do not have any side effects from the flu vaccine. Some have soreness or swelling at the site of the shot or mild side effects, such as headache or a low fever.

Where Can My Family Get the Flu Vaccine?

The flu vaccine is available at:

  • doctors’ offices
  • public, employee, and university health clinics
  • most drugstores
  • some supermarkets and big-box stores
  • some community groups or centers
  • some schools

Reviewed by: Elana Pearl Ben-Joseph, MD Date reviewed: September 2019

Flu vaccine FAQs

When am I most at risk from flu?

Flu circulates every winter and generally peaks in December and January. This means many people get ill around the same time.

But it’s impossible to predict how many cases of flu there will be each year or exactly when it’ll peak.

Does everyone need a flu vaccine?

No, just people who are at particular risk of problems if they catch flu.

Ask a GP about having an NHS flu vaccination if:

  • you’re aged 65 or over
  • you’re pregnant
  • you have a serious medical condition
  • you live in a residential or nursing home
  • you’re the main carer for an elderly or disabled person whose welfare may be at risk if you fall ill
  • your child is in an at-risk group and is aged 6 months or over

Some pharmacies also offer free NHS flu vaccination to adults and social care workers in the categories listed above. They do not offer this service for children.

You should also have the flu vaccination if you’re a healthcare or social care worker directly involved in patient care.

You may also be able to have the flu vaccine at your GP surgery or a local pharmacy offering the service if you’re a frontline health or social care worker employed by a:

  • registered residential care or nursing home
  • registered homecare organisation
  • hospice

Find out more about who should have the flu vaccine

Why are certain groups targeted for the flu vaccine?

Complications such as bronchitis and pneumonia are more common in people with other conditions, especially if they’re also older.

In long-stay residential homes, vaccination helps prevent the rapid spread of flu among residents.

Is my child entitled to the flu vaccine?

Children eligible for the free nasal spray flu vaccine include:

  • children aged 2 and 3 on 31 August 2019
  • children in primary school
  • children with a health condition that puts them at greater risk from flu

How long will the flu vaccine protect me for?

The flu vaccine will provide protection for you for the upcoming flu season. People eligible for flu vaccination should have the vaccine each year.

What type of flu vaccine will I be offered?

There are several types of flu vaccine.

You’ll be offered 1 that’s most effective for you, depending on your age:

  • children aged 2 to 17 in an eligible group are offered a live attenuated quadrivalent vaccine (LAIV), given as a nasal spray
  • adults aged 18 to 64 who are either pregnant, at increased risk from flu because of a long-term health condition, or a frontline health or social care worker are offered a quadrivalent injected vaccine – the vaccine offered will have been grown either in eggs or cells (QIVe or QIVc), both of which are considered to be equally effective
  • adults aged 65 and over will be offered either an adjuvanted trivalent injected vaccine grown in eggs (aTIV) or a cell-grown quadrivalent injected vaccine (QIVc) – both vaccines are considered to be equally effective

If your child is aged between 6 months and 2 years old and is in a high-risk group for flu, they’ll be offered an injected flu vaccine as the nasal spray is not licensed for children under 2.

Can I have the flu vaccine while I’m taking antibiotics?

Yes, it’s fine to have the flu vaccine while you’re taking a course of antibiotics, provided you’re not ill with a high temperature.

How long does the flu vaccine take to become effective?

It takes between 10 and 14 days for your immune system to respond fully after you have had the flu vaccine.

If I had the flu vaccine last year, do I need it again now?

Yes. The viruses that cause flu can change every year, which means the flu (and the vaccine) this winter may be different from last winter.

Can the flu vaccine cause flu?

No. The vaccine does not contain any live viruses, so it cannot cause flu.

You may get a slight temperature and aching muscles for a couple of days afterwards, and your arm may feel a bit sore where you had the injection.

Other reactions are rare, and flu vaccines have a good safety record.

For children, the nasal spray vaccine cannot cause flu because the viruses in it have been weakened to prevent this happening.

When is the best time to get my flu vaccine?

The best time to have a flu vaccine is in the autumn, from the beginning of October to the end of November.

If you have missed this time, you can have the flu vaccine later in the winter, although it’s best to get it earlier.

Is there anyone who cannot have a flu vaccine?

Yes. You should not have the flu vaccine if you have ever had an allergic reaction to a flu vaccine or 1 of its ingredients. This happens very rarely.

You also need to take precautions if you have an egg allergy.

Find out who should not have the flu vaccine

Can I get the flu vaccine privately?

Adults who are not eligible for a flu vaccine on the NHS can pay for a flu vaccination privately.

The flu vaccine may be available from pharmacies or in supermarkets.

It’s provided on a private patient basis and you have to pay. The vaccine costs up to £20.

Why is it recommended that healthcare workers are vaccinated?

Vaccination prevents healthcare workers passing flu on to, or getting flu from, their patients.

It also helps the NHS to keep running effectively during a flu outbreak, when GPs and hospital services are particularly busy.

Can I have a flu vaccine if I’m breastfeeding?

Yes. The vaccine poses no risk to a breastfeeding mother or her baby, or to pregnant women.

Is it OK to have the flu vaccine during pregnancy?

Yes. In fact it’s important to get the flu vaccine if you’re pregnant.

It’s safe to have at any stage of pregnancy, including in the first trimester and right up to the expected due date.

It helps protect the mother-to-be and her newborn baby from catching flu.

Find out more about the flu vaccine in pregnancy

Yes, It Is Possible To Get Your Flu Shot Too Soon

“So some might worry that if got vaccinated very early and flu didn’t show up until very late, it might not work as well,” he says. But other studies show “you still have protection from the shot you got last year,” Treanor adds, “if it’s a year when the strains didn’t change.”

In any given flu season, the effectiveness of immunization varies, partly dependent on how well the vaccine matches the strain of flu virus that’s predominant that year. In the overall population, the CDC says studies show a vaccine can reduce the risk of flu by about 50 to 60 percent when the vaccine is well-matched.

It’s especially important to vaccinate children, to help keep parents and grandparents healthy, as well as the kids themselves, doctors say. While most people who get the flu recover, it is a serious disease responsible for many deaths each year, particularly among older adults and young children.

The intensity of illness provoked by each influenza strain can vary, too; U.S. deaths associated with the flu have ranged from about 3,300 a year to 49,000 in the past 31 seasons.

To develop vaccines, manufacturers and scientists study what’s circulating in the Southern Hemisphere during its winter flu season — June, July and August. Then, based on that evidence, they forecast what flu strains might be circulating in the U.S. the following November, December and January, and incorporate that information into flu vaccines that are generally ready by late July.

For the upcoming season, the vaccines will include three or four strains — including two influenza A strains, an H1N1 and an H3N2, as well as one or two B strains, according to the CDC. The federal health officials recommend that everyone older than 6 months gets vaccinated, unless they have a health condition that would prevent it.

The vaccines can’t give a person the flu because the virus is killed before it’s used in the shot. This year, the nasal vaccine — a squirt of liquid that includes a live attenuated virus — is not recommended for use, as studies showed it was not effective during several of the past flu seasons.

So, talk to your doctor, and weigh your options for the timing of that flu shot. “The ideal time is between Halloween and Thanksgiving,” says Haynes, who specializes in the immunity of older people. “If you can’t wait, and the only chance is to get it in September, then go ahead and get it. It’s best to get it early rather than not at all.”

Kaiser Health News is a service of the nonprofit Kaiser Family Foundation. Neither one is affiliated with the health insurer Kaiser Permanente. Follow Julie Appleby on Twitter: @Julie_appleby.

When is the best time to get a flu shot?

In a new study published in the journal Vaccine, Annette Regan, PhD, of the Texas A&M School of Public Health, and colleagues from institutions in the United States and Australia examined the effectiveness of the influenza vaccine in Australia during the 2016 Southern Hemisphere influenza season. They were specifically interested in examining the effectiveness of vaccination as the seasonal epidemic progressed.

To accomplish this, the researchers relied on data from three health care surveillance systems in Australia. They found more than 5,000 patients who had influenza-like symptoms. Of these, 1,085 patients were tested for influenza, and 447 tested positive for influenza. The data also included a breakdown of which strain of influenza each patient had, along with patient demographic information and when, if at all, patients had received a vaccination. Patients with influenza-like illness who tested negative for influenza were used as a control group in calculating vaccine effectiveness.

Flu vaccine effectiveness based on timing

Their analysis found that the 2016 influenza vaccine in Australia had an overall effectiveness of 40 percent. Vaccine effectiveness for specific strains ranged from 42 to 67 percent for different influenza A viruses, but the 2016 vaccine was ineffective against influenza B viruses.

Regan and colleagues also found that the vaccine was most effective in patients with a record of vaccination less than three months before symptom onset. Vaccine effectiveness at three months after vaccination was approximately 40 percent, and that effectiveness declined after that, with a 25 percent effectiveness at four months.

Similar flu vaccine effectiveness in European and U.S. studies

“Several other European and U.S. studies have identified similar patterns in declining effectiveness, which may suggest that immunity to influenza wanes within months following vaccination,” Regan said. “This would suggest vaccination as close to the influenza season as possible would offer the best protection.”

However, Regan and her colleagues noted that the reasons for this decrease in effectiveness was unclear. Their findings could have also been due to changes in the types of strains most prominent at different points in the influenza season or various other confounding factors. Thus, further research is needed to determine why this decreasing effectiveness occurred, as it could affect when vaccinations are first offered with respect to influenza season.

The findings from this study show that the influenza vaccine was moderately effective in 2016 and that vaccine effectiveness changed over time. These results point to a need for further research into vaccine effectiveness, especially around the duration of protection of vaccination.

“Because influenza can be a severe disease, this research is important for optimizing the administration of seasonal vaccination campaigns, which cost over $1 billion annually in the United States alone,” Regan said.

— Rae Lynn Mitchell

Is It Too Early to Get a Flu Shot?

It seems like summer just ended, yet pharmacies and schools are already telling us to line up for our flu shots.

But the Centers for Disease Control and Prevention (CDC) recommended today that people get their vaccines for the 2018-19 flu season by the end of October. In other words, two solid months from now.

The exact timing of flu season in the U.S. varies every year, but it’s typically in fullest frenzy in December, January, and February. That’s when you want to make sure you’re best protected. “We know that antibodies peak four to six weeks after getting a vaccine and then slowly go down over the next six months,” explains Ann Falsey, MD, professor of medicine in the infectious disease unit at the University of Rochester Medical Center. “There are some theoretical concerns toward spring that you might be less protected if you get vaccinated too early.”

RELATED: Here’s Where You Can Get a Free Flu Shot Right Now—With or Without Insurance

She advises her patients to get their flu shots in late September or early October–and definitely by Halloween–so they’re protected before flu activity peaks in those winter months.

You’ll have some measure of protection even earlier, as antibodies–proteins that develop in the blood as part of the immune system’s natural response to potentially harmful invaders like the influenza virus–initially kick in about two weeks after you’re vaccinated.

RELATED: Why You Should Get the Flu Shot Every Year

But timing of the flu season and, therefore, the vaccine, is just one question mark factoring into how effective any vaccine will be. The other is how well the flu strains in the vaccine match what’s actually circulating. And that’s always a bit of a guessing game.

The Southern Hemisphere is still having its flu season (ending more or less next month), and it’s what’s happening there that guides public health decisions up here.

“Experts monitor the strains circulating in the Southern Hemisphere to see what they would predict to circulate in the Northern Hemisphere,” says Dr. Falsey, then vaccine manufacturers get started months in advance. “They have to take their best estimate and pick what strains they think are going to be circulating. Most of the time they get it right, but occasionally the flu can be pesky and a strain can pop up that is divergent,” she says.

RELATED: If You Have an Egg Allergy, Can You Still Get a Flu Shot?

Today’s CDC announcement stated that this season’s vaccines have been updated to better match circulating viruses. Last year’s vaccine was not well matched, reducing the effectiveness to about 36%.

“Everybody would love to have 100% efficacy to prevent infection, but that has never been the case,” says Dr. Falsey. “Generally, if you have efficacy in the 50% to 60% range, I think people would be happy with that.” Not only does that prevent some infections, it also cuts down on flu-related complications, including hospitalizations and deaths.

The CDC also announced that the nasal spray flu vaccine will again be available for certain individuals this year after a two-season hiatus. Most vaccines for the upcoming flu season will be quadrivalent, meaning they protect against four different virus strains.

RELATED: Can You Still Get the Flu Shot If You’re Sick?

So why are pharmacies and schools pushing vaccines now? It’s possible that the specter of one kid getting sick and then dozens or hundreds following suit is just too terrible to comprehend. Or maybe pharmacies don’t want a stampede of vaccine seekers in October.

The CDC recommends that all individuals age 6 months and older who don’t have a specific reason not to get vaccinated–like a history of allergic reactions to the flu shot–do so. It’s especially important in older adults, who tend to have more and worse complications from the flu, as well as in people who have certain chronic health conditions or who are pregnant.

In addition to pharmacies and schools, you can also get the flu vaccine at your doctor’s office, urgent-care clinics, and many workplaces for free.

Ultimately, there’s really no bad time to get vaccinated. You might be a little early or late, but do it anyway. And ideally, do it around the end of September to the end of October.

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Key Facts About Seasonal Flu Vaccine

Flu Vaccination

Why should people get vaccinated against flu?

Influenza is a potentially serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza infection can affect people differently, but millions of people get flu every year, hundreds of thousands of people are hospitalized and thousands to tens of thousands of people die from flu-related causes every year. An annual seasonal flu vaccine is the best way to help protect against flu. Vaccination has been shown to have many benefits including reducing the risk of flu illnesses, hospitalizations and even the risk of flu-related death in children.

How do flu vaccines work?

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are used to make the vaccine.

The seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season. Most flu vaccines in the United States protect against four different flu viruses (“quadrivalent”); an influenza A (H1N1) virus, an influenza A (H3N2) virus, and two influenza B viruses. There are also some flu vaccines that protect against three different flu viruses (“trivalent”); an influenza A (H1N1) virus, an influenza A (H3N2) virus, and one influenza B virus. Two of the trivalent vaccines are designed specifically for people 65 and older to create a stronger immune response.

What kinds of flu vaccines are available?

Yes. There are different influenza vaccine manufacturers and multiple influenza vaccine products licensed and recommended for use in the United States.

CDC recommends use of any licensed, age-appropriate influenza vaccine during the 2019-2020 influenza season, including inactivated influenza vaccine , recombinant influenza vaccine , or live attenuated influenza vaccine (LAIV). No preference is expressed for any influenza vaccine over another. Both trivalent (three-component) and quadrivalent (four-component) influenza vaccines will be available.

Trivalent influenza vaccines include:

  • A trivalent influenza shot made with adjuvant (Fluad), licensed for people 65 years and older.
  • A high-dose influenza vaccine (Fluzone High-Dose), licensed for people 65 years and older.

Quadrivalent flu vaccines include:

  • Standard-dose quadrivalent influenza shots that are manufactured using virus grown in eggs. These include Afluria Quadrivalent, Fluarix Quadrivalent, FluLaval Quadrivalent, and Fluzone Quadrivalent. Different influenza shots are licensed for different age groups. Some are licensed for children as young as 6 months of age. Most influenza shots are given in an arm muscle with a needle. One quadrivalent influenza shot (Afluria Quadrivalent) can be given either with a needle (for people aged 6 months and older) or with a jet injector (for people aged 18 through 64 years only).
  • A quadrivalent cell-based influenza shot (Flucelvax Quadrivalent) containing virus grown in cell culture, which is licensed for people 4 years and older. This season, all four of the vaccine viruses used in Flucelvax have been grown in cells, making the vaccine totally egg-free.
  • Recombinant quadrivalent influenza shot (Flublok Quadrivalent), an egg-free vaccine, approved for people 18 years and older.

There are many vaccine options to choose from, but the most important thing is for all people 6 months and older to get an influenza vaccine every year. If you have questions about which vaccine is best for you, talk to your doctor or other health care professional. More information on approved influenza vaccines for the 2019-2020 influenza season, and age indications for each vaccine are available in CDC’s Table: U.S. Influenza Vaccine Products for the 2019-20 Season

Are any of the available flu vaccines recommended over others?

No. For the 2019-2020 influenza season, CDC and its Advisory Committee on Immunization Practices (ACIP) recommends annual influenza vaccination for everyone 6 months and older with any licensed age-appropriate influenza vaccine including inactivated influenza vaccine (IIV), recombinant influenza vaccine (RIV4) or live attenuated influenza vaccine (LAIV4) with no preference expressed for any one vaccine over another.

Who should get vaccinated this season?

Everyone 6 months of age and older should get an influenza (flu) vaccine every season with rare exception. CDC’s Advisory Committee on Immunization Practices has made this recommendation since the 2010-11 influenza season.

Vaccination to prevent flu is particularly important for people who are at high risk of developing serious flu complications. See People at High Risk of Developing Flu-Related Complications for a full list of age and health factors that confer increased risk.

More information is available at Who Should Get Vaccinated Against Influenza.

Who Should Not Be Vaccinated?

Different influenza vaccines are approved for use in different age groups. In addition, some vaccines are not recommended for certain groups of people. Factors that can determine a person’s suitability for vaccination, or vaccination with a particular vaccine, include a person’s age, health (current and past) and any allergies to influenza vaccine or its components.

  • People who cannot get a influenza shot
  • People who should talk to their doctor before getting the influenza shot

When should I get vaccinated?

You should get a flu vaccine before flu viruses begins spreading in your community, since it takes about two weeks after vaccination for antibodies to develop in the body and provide protection against flu. Make plans to get vaccinated early in fall, before flu season begins. CDC recommends that people get a flu vaccine by the end of October. Getting vaccinated later, however, can still be beneficial and vaccination should continue to be offered throughout the flu season, even into January or later.

Getting vaccinated early (for example, in July or August) is likely to be associated with reduced protection against flu infection later in the flu season, particularly among older adults.

Children who need two doses of vaccine to be protected should start the vaccination process sooner, because the two doses must be given at least four weeks apart.

Where can I get a flu vaccine?

Flu vaccines are offered in many doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.

Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or workplace.

Visit the HealthMap Vaccine Finderexternal icon to locate where you can get a flu vaccine.

Why do I need a flu vaccine every year?

A flu vaccine is needed every season for two reasons. First, a person’s immune protection from vaccination declines over time, so an annual vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, flu vaccines may be updated from one season to the next to protect against the viruses that research suggests may be most common during the upcoming flu season. For the best protection, everyone 6 months and older should get vaccinated annually.

Does flu vaccine work right away?

No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. That’s why it’s best to get vaccinated before influenza viruses start to spread in your community.

Vaccine Effectiveness

Influenza vaccine effectiveness (VE) can vary from season to season. The protection provided by an influenza vaccine depends on the age and health status of the person getting the vaccine, and the similarity or “match” between the viruses used to produce vaccine and those in circulation.

While influenza vaccine varies in how well it works, every season influenza vaccines prevent millions of influenza illnesses, tens of thousands of hospitalizations and thousands of deaths.

For more information, see Vaccine Effectiveness – How well do Flu Vaccines Work.

Can I get seasonal flu even though I got a flu vaccine this year?

Yes. It’s possible to get sick with flu even if you have been vaccinated (although you won’t know for sure unless you get a flu test). This is possible for the following reasons:

  • You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (Antibodies that provide protection develop in the body about 2 weeks after vaccination.)
  • You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that circulate every year. A flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.
  • Unfortunately, some people can become infected with a flu virus a flu vaccine is designed to protect against, despite getting vaccinated. Protection provided by flu vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, a flu vaccine works best among healthy younger adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. Flu vaccination is not a perfect tool, but it is the best way to protect against flu infection.

What protection does a flu vaccine provide if I do get sick with flu?

Some people who get vaccinated may still get sick. However, flu vaccination has been shown in some studies to reduce severity of illness in people who get vaccinated but still get sick. A 2017 study showed that flu vaccination reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized adults with flu. Another study in 2018 showed that a vaccinated adult who was hospitalized with flu was 59 percent less likely to be admitted to the ICU than someone who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent 4 fewer days in the hospital than those who were not vaccinated.

Vaccine Benefits

What are the benefits of flu vaccination?

There are many reasons to get an influenza (flu) vaccine each year. Below is a summary of the benefits of flu vaccination, and selected scientific studies that support these benefits.

  • Flu vaccination can keep you from getting sick with flu.
    • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2017-2018, flu vaccination prevented an estimated 6.2 million influenza illnesses, 3.2 million influenza-associated medical visits, 91,000 influenza-associated hospitalizations, and 5,700 influenza-associated deaths.
    • During seasons when the flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40 percent to 60 percent.
  • Flu vaccination can reduce the risk of flu-associated hospitalization for children, working age adults, and older adults.
    • Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2017-2018, flu vaccination prevented an estimated 91,000 flu-related hospitalizations.
    • A 2014 studyexternal icon showed that flu vaccine reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
    • In recent years, flu vaccines have reduced the risk of flu-associated hospitalizations among older adultsexternal icon on average by about 40%.
    • A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an intensive care unit (ICU) with flu by 82 percent.
  • Flu vaccination is an important preventive tool for people with chronic health conditions.
    • Flu vaccination has been associated with lower rates of some cardiac eventsexternal icon among people with heart disease, especially among those who had had a cardiac event in the past year.
    • Flu vaccination can reduce worsening and hospitalization for flu-related chronic lung disease, such as in persons with chronic obstructive pulmonary disease (COPD).
    • Flu vaccination also has been shown in separate studies to be associated with reduced hospitalizations among people with diabetesexternal icon and chronic lung diseaseexternal icon.
  • Flu vaccination helps protect women during and after pregnancy.
    • Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant women by about one-half.
    • A 2018 studyexternal icon that included influenza seasons from 2010-2016 showed that getting a flu shot reduced a pregnant woman’s risk of being hospitalized with flu by an average of 40 percent.
    • A number of studies have shown that in addition to helping to protect pregnant women, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth, when he or she is not old enough to be vaccinated.
  • Flu vaccine can be life-saving in children.
    • A 2017 study was the first of its kind to show that flu vaccination can significantly reduce a child’s risk of dying from flu.
  • Flu vaccination has been shown in several studies to reduce severity of illness in people who get vaccinated but still get sick.
    • A 2017 study showed that flu vaccination reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized flu patients.
    • A 2018 studyexternal icon showed that among adults hospitalized with flu, vaccinated patients were 59 percent less likely to be admitted to the ICU than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients on average spent 4 fewer days in the hospital than those who were not vaccinated.
  • Getting vaccinated yourself may also protect people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.

*References for the studies listed above can be found at Publications on Influenza Vaccine Benefits. Also, see the A Strong Defense Against Flu: Get Vaccinated! pdf icon fact sheet.

Vaccine Match

What is meant by a “good match” between viruses in the vaccine and circulating influenza viruses?

A “good match” is said to occur when the flu vaccine viruses used to produce flu vaccine and the viruses circulating among people during a given influenza season are “like” one another such that the antibodies produced by vaccination protect against infection with circulating viruses.

What if circulating viruses and the vaccine viruses are different?

During seasons when one or more of the circulating viruses are different or “drifted” from the vaccine viruses, vaccine effectiveness against the drifted viruses can be reduced. It’s important to remember that flu vaccine protects against three or four different flu viruses and multiple viruses usually circulate during any one season. Even if the effectiveness of the vaccine is reduced against one virus it can still be effective at preventing flu illness caused by the other circulating viruses. For these reasons, CDC continues to recommend flu vaccination for everyone 6 months and older even if vaccine effectiveness against one or more viruses is reduced.

Why is there sometimes not a good match between a vaccine virus and circulating viruses?

Flu viruses are constantly changing (called “antigenic drift”) – they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. (For more information about the vaccine virus selection process visit Selecting the Viruses in the Influenza (Flu) Vaccine.) Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses used to produce vaccine.

The production process for some seasonal vaccines also may impact how well vaccine works against certain viruses, especially influenza A (H3N2) viruses. Growth in eggs is part of the production process for most seasonal flu vaccines. While all influenza viruses undergo changes when they are grown in eggs, changes in influenza A(H3N2) viruses are more likely to result in antigenic changes compared with changes in other influenza viruses. These so-called “egg-adapted changes” are present in most of the vaccine viruses recommended for use in egg-based vaccine production and may reduce their potential effectiveness against circulating influenza viruses. Advances in vaccine production technologies (for example, cell-based and recombinant technology) and advanced molecular techniques are being explored as ways to improve flu vaccine effectiveness. Learn more by visiting, Advancements in Influenza Vaccines.

Will this season’s vaccine be a good match for circulating viruses?

It’s not possible to predict with certainty if a flu vaccine will be like circulating flu viruses because flu viruses are constantly changing. A flu vaccine is made to protect against the flu viruses that research and surveillance indicate will likely be most common during the season. Over the course of flu season, CDC studies samples of circulating flu viruses to evaluate how close a match there is between viruses used to make the flu vaccine and circulating flu viruses. More information about the 2019-2020 flu season and recommended vaccines is available.

Vaccine Side Effects (What to Expect)

Can a flu vaccine give me flu?

No, a flu vaccine cannot cause flu illness. Flu vaccines that are administered with a needle (flu shots) are currently made in two ways: the vaccine is made either with a) flu vaccine viruses that have been killed (inactivated) and are therefore not infectious, or b) with proteins from a flu vaccine virus instead of flu vaccine viruses (which is the case for recombinant influenza vaccine). Nasal spray vaccine is made with attenuated (weakened) live flu viruses, and also cannot cause flu illness. The weakened viruses are cold-adapted, which means they are designed to only cause infection at the cooler temperatures found within the nose. The viruses cannot infect the lungs or other areas where warmer temperatures exist.

What side effects can occur after getting a flu vaccine?

While a flu vaccine cannot give you flu illness, there are different side effects that may be associated with getting a flu shot or a nasal spray flu vaccine. These side effects are mild and short-lasting, especially when compared to symptoms of bad case of flu.

A flu shot: The viruses in a flu shot are killed (inactivated), so you cannot get flu from a flu shot. Some minor side effects that may occur are:

  • Soreness, redness, and/or swelling where the shot was given
  • Headache (low grade)
  • Fever
  • Muscle aches
  • Nausea
  • Fatigue

The nasal spray: The viruses in the nasal spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. In children, side effects from the nasal spray may include:

  • Runny nose
  • Wheezing
  • Headache
  • Vomiting
  • Muscle aches
  • Fever (low grade)

In adults, side effects from the nasal spray vaccine may include:

  • Runny nose
  • Headache
  • Sore throat
  • Cough

If these problems occur, they begin soon after vaccination and usually are mild and short-lived. A flu shot, like other injections, can occasionally cause fainting. Tell your provider if you feel dizzy or have vision changes or ringing in the ears. As with any medicine, there is a very remote chance of a vaccine causing a severe allergic reaction, other serious injury, or death. People who think that they have been injured by a flu vaccine can file a claim for compensation from the National Vaccine Injury Compensation Program (VICP)external icon.

More information about the safety of flu vaccines is available at Influenza Vaccine Safety.

Vaccine Supply and Distribution

How much influenza vaccine is projected to be available for the 2019-2020 influenza season?

Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. Vaccine manufacturers have projected that they will supply as many as 162 million to 169 million doses of influenza vaccine for the 2019-2020 season.

Where can I find information about vaccine supply?

Information about vaccine supply is available on the CDC’s Vaccine Supply & Distribution webpage.

Special Consideration Regarding Egg Allergy

People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV, RIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions.

Flu shot season is upon us.

Three years ago, STAT laid out some of the questions surrounding flu vaccination in an article you can find here. Lots of flu vaccine studies have been published in the interval — clearing up some of the questions we raised, adding to the confusion with others.

Given that a lot of you are either about to roll up a sleeve or are debating whether you should, we decided to revisit the issues we explored previously, based on new information. We’ll also raise a few more questions percolating in the world of influenza science.

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Is it too soon to get your flu shot? And is it possible to wait too long?

One of the questions about flu vaccine relates to how long its protection lasts. In particular, researchers have been exploring whether that protection erodes during the course of a single season — and if it does, how quickly.

If you get vaccinated in August or September and flu season really only takes off in January, how much protection will you have left? On the other hand if you wait until December to get your shot, what if flu season starts early?

It’s now pretty clear that “intra-season waning” — the erosion of protection within a season — does occur. A study from the Centers for Disease Control and Prevention published in 2017 estimated the decline at about 7% a month from the time of vaccination. A study from the Kaiser Permanente Vaccine Study Center published this spring suggested the erosion was more rapid: roughly 16% for every block of 28 days after vaccination.

Marc Lipsitch, an infectious diseases epidemiologist at Harvard University’s T.H. Chan School of Public Health, had concerns that the methodology used in the latter study might have been flawed. He worked with the researchers to reanalyze the data using a different study design. They reached the same conclusion.

“I think the best estimate at the moment with the tools we have — which are pretty good but not perfect — is that there is substantial waning,” Lipsitch said.

This is a situation, though, where what’s best from a scientific point of view isn’t necessarily what’s doable from a real world point of view. The annual flu vaccination program is a massive endeavor.

About 45% of the U.S. population gets a flu shot, more than in any other country in the world. Given the demands that places on health care delivery — and the evidence that people who leave getting a flu shot too late often don’t get one in the end — the CDC recommends people try to get vaccinated before the end of October.

“It is a big logistic issue for the health care system in the U.S. every year,” said Dr. Dan Jernigan, director of the agency’s influenza division. “We think getting it around the October time frame is good, but any time from September to November is better than not getting it.”

Still, given the evidence of waning protection, Lipsitch argued it is “perfectly reasonable and probably best” for people to get a flu shot later, if they can, and for flu shot clinic organizers to keep waning in mind. “It’s no harder to hold three flu clinics in October and November than it is to hold them in September and August.”

Is FluMist effective? Can I get it?

FluMist, the only non-injected influenza vaccine, has been through a rough patch. This year could have been the vaccine’s comeback — but it won’t be.

Made by AstraZeneca, FluMist suffered a major setback when the expert committee that advises the CDC on vaccines recommended it not be used for the 2016-2017 flu season, and later the 2017-2018 flu season as well. Data collected over the previous three years suggested it hadn’t been effective. That virtually sealed off most of the U.S. market to FluMist for two years.

In 2018 the CDC committee concluded changes that AstraZeneca made to the vaccine appeared to have solved the effectiveness problem, and it again recommended FluMist could be used.

But by the time that recommendation was made, many of the companies that buy flu vaccine in bulk had already placed their orders for the 2018-2019 season. And the American Academy of Pediatrics wasn’t convinced the changes had resolved FluMist’s issues; it recommended that pediatricians urge families to give their children flu shots instead.

This year all of the constraints of the previous three seasons were lifted. But then new misfortunate befell FluMist. AstraZeneca had problems producing the viruses needed for two of the four components of the vaccine.

The U.S. market is getting a paltry amount — about 758,000 doses. Parents looking for FluMist will have a hard time finding it this year. It could be even harder in other countries. Pediatricians in Israel and Canada were informed there would be no FluMist available there for the coming flu season.

AstraZeneca has declined to make anyone available to talk about the situation. But the company confirmed that it had yield problems for the parts of the vaccine that protect against influenza A viruses H1N1 and H3N2. (The vaccine also protects against two influenza B viruses.)

This occurs from time to time with vaccine production. It is unfortunate for AstraZeneca, though, that it happened in a year when FluMist might have been poised for a resurgence.

Do I have to be worried about the statin factor when getting a flu shot?

There have been concerns that commonly used cholesterol-lowering drugs, statins, might actually undermine the effectiveness of flu vaccine.

A couple of studies had raised questions about the possibility that the drugs might dampen the immune response triggered by vaccine. That was particularly worrying because the people who take statins — adults in late-middle age and older — are often the people who are at highest risk of becoming seriously ill or dying from influenza. (At least in H3N2 flu seasons; more on this later.)

The evidence amassed in recent years, however, suggests these fears were not founded. Researchers at the Marshfield Clinic Research Institute in Marshfield, Wis., looked at data over six flu seasons and saw no significant lowering of vaccine effectiveness among statin users.

And researchers from the Food and Drug Administration and the CDC analyzed the medical records of 2.8 million Medicare beneficiaries. They saw no sign that people who used statins and were vaccinated were more likely to have serious bouts of flu than people who were vaccinated but didn’t take statins.

For the CDC, this question is answered. “We’re not doing anything further with that now,” Jernigan said.

Can repeated vaccination actually backfire?

There’s been a growing belief that getting a flu shot year after year can impede the immune system’s ability to generate a strong response to the vaccine.

It’s not thought that this phenomenon happens every year. But in some years when the viruses in the vaccine haven’t been updated but the viruses that are circulating are different from the vaccine version, people who have been repeatedly vaccinated may end up being less well protected. Influenza researchers call this “negative interference.”

Dr. Danuta Skowronski of the British Columbia Center for Disease Control has published papers showing this effect. She said the research community’s consensus appears to be accepting that this is real.

“There really has been a shift, a palpable shift, from ‘Are these signals real?’ to almost a sense of ‘Of course they’re real. Now why?’” she said.

Dr. Mark Loeb, a flu research at McMaster University in Hamilton, Ontario, looks at the issue a different way. Loeb’s group conducted a massive meta-analysis, looking at all of the scientific literature on the question, screening thousands of papers. The conclusion: Repeat vaccination isn’t consistently undermining the protection the vaccine offers.

“To me the bottom line is the data to date don’t really support a reduction in vaccine efficacy with repeat flu vaccination,” Loeb said. “They don’t rule it out completely. So I think it’s still a bit of an open question.”

Loeb doesn’t rule it out; Skowronski definitely rules it in — sometimes. But neither thinks current recommendations to get annual flu shots should be changed.

A separate effect seen with influenza — known as original antigenic sin or imprinting — is based on the idea that the first flu viruses you encounter in your life leave an indelible mark on your immune system. If your first infection was caused by an H3N2 virus, you’ll always produce more antibodies to H3 viruses when you get vaccinated than you will to the other influenza A viruses, H1N1, and vice-versa.

This idea has really taken root in the flu research community. The data on who gets sickest each flu season are making the pattern “very clear,” Jernigan said, pointing to a recently published paper by Alicia Budd of the CDC.

It shows that since the 2009 flu pandemic, caused by a new H1N1 virus, different age groups are getting hospitalized with severe flu infections in H1N1 years.

The mantra that flu seasons are hardest on the elderly may shift to “some flu seasons.” The elderly fared pretty well in the H1N1 pandemic — their immune systems recognizing it as a distant relative of a flu virus they’d encountered earlier in life. But people who were born in the late 1950s and the 1960s had their first infections with other viruses, and H1N1 viruses are a bigger threat for them.

An earlier version of this story said people who have been repeatedly vaccinated might be more likely to contract influenza over time. In fact, repeated vaccination might diminish the protection the vaccine provides some people over time.

More than 80,000 people died from influenza related illnesses last winter—a staggering number and one of the highest in over a decade according to the CDC. The importance of getting a flu shot can’t be overstated, so why do some people avoid it?

“Misinformation is one reason,” said Dr. Marita Michelin, Chair of Emergency Medicine at Newark-Wayne Community Hospital. “There are a lot of myths out there about the flu shot that simply aren’t true.”

One of those misconceptions is the belief that the flu shot can cause the flu.

Read Our New Flu Guide

A recent survey found that more than half of parents with children under age 18 believe that their child can get the flu from the flu shot. In fact, it’s not possible to get the flu from the flu vaccine, since the vaccine contains deactivated or weakened ingredients.

“There’s a small window of about two weeks from when you get the vaccine that you are susceptible to getting the flu, since it takes time for the vaccine to provide protection,” said Dr. Michelin. “Anyone who gets the virus during this window does so because the vaccine hasn’t kicked in yet, but certainly not because the vaccine has given you the flu.”

Another common myth, said Dr. Michelin, is people thinking because they never get sick, they won’t get the flu.

“If you’ve rarely been ill with the flu, you could be even more susceptible,” explained Dr. Michelin.“More importantly, no one wants to be the one who spreads the flu to their friends and family.”

Best Time to Get the Flu Shot

Getting your flu shot before the flu season begins provides the best protection from the virus. Antibodies that protect against influenza take about two weeks to build up after receiving the shot, which is why it’s important to get vaccinated as soon as the vaccination becomes available.

Dr. Michelin says that recommendations are that everyone over the age of six months should receive the vaccine annually.

“The vaccine will not only help to protect you from getting the flu, but new research shows it will also help lessen the severity of the symptoms should you get the flu,” she explained. “The influenza virus is constantly changing. Each year, researchers work to identify the virus strains they believe will cause the most illness and the vaccine is made off their recommendations. So it is important to get vaccinated every year.”

Children between six months and eight years of age may need two doses to be fully protected from the flu. Additionally, a higher potency vaccine is available to those over 65.

Dr. Michelin also emphasized the value of flu vaccines for pregnant women. Complications can arise from the flu in pregnant women including pneumonia and hospitalizations. The benefit for both the mother and the baby are critical.

Lastly, Dr. Michelin stressed the significance of hand hygiene.

“Whether you use an alcohol based hand sanitizer or soap and water, it’s crucial to keep your hands clean so you don’t spread germs to others or contract the disease yourself,” she said.

The flu vaccine is currently available at your Rochester Regional Health primary care location along with additional walk-in locations sponsored by Monroe County.

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Flu shot too early

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