Flu Vaccination

Why should people get vaccinated against the flu?

Influenza (flu) is a potentially serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and flu can affect people differently, but during typical flu seasons, 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. Flu can mean a few days of feeling bad and missing work, school, or family events, or it can result in a more serious illness. Complications of flu can include bacterial pneumonia, ear infections, sinus infections, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. An annual seasonal flu vaccine is the best way to help reduce the risk of getting flu and any of its potentially serious complications. Vaccination has been shown to have many benefits including reducing the risk of flu illnesses, hospitalizations, and even the risk of flu-related death. While some people who get a flu vaccine may still get sick with influenza, flu vaccination has been shown in several studies to reduce the severity of illness.

How do flu vaccines work?

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against flu illness.

Seasonal flu vaccines are designed to protect against the influenza viruses that research indicates will be most common during the upcoming season. All flu vaccines in the United States are “quadrivalent” vaccines, which means they protect against four different flu viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus, and two influenza B viruses.

Flu Vaccine Options

For people younger than 65 years, CDC does not preferentially recommend any licensed, age-appropriate influenza (flu) vaccine over another during the 2022-2023 flu season. Options for this age group include inactivated influenza vaccine [IIV], recombinant influenza vaccine [RIV], or live attenuated influenza vaccine (LAIV), with no preference for any flu vaccine over another.

New for this season: For people 65 years and older, there are three flu vaccines that are preferentially recommended over standard-dose, unadjuvanted flu vaccines. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine, and Fluad Quadrivalent adjuvanted flu vaccine. More information is available at Flu & People 65 Years and Older.

All flu vaccines for the 2022-2023 season are quadrivalent vaccines, designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses. Different vaccines are licensed for use in different age groups, and some vaccines are not recommended for some groups of people.

Available flu vaccines include:

Standard-dose flu shots are manufactured using virus grown in eggs. Several different brands of standard dose flu shots are available, including Afluria Quadrivalent, Fluarix Quadrivalent, FluLaval Quadrivalent, and Fluzone Quadrivalent. These vaccines are approved for use in children as young as 6 months. Most flu shots are given in the arm (muscle) with a needle. Afluria Quadrivalent can be given either with a needle (for people 6 months and older) or with a jet injector (for people 18 through 64 years only).

A cell-based flu shot (Flucelvax Quadrivalent) containing virus is grown in cell culture, which is approved for people 6 months and older. This vaccine is completely egg-free.

A recombinant flu shot (Flublok Quadrivalent) which is a completely egg-free flu shot that is made using recombinant technology and is approved for use in people 18 years and older. This shot is made without flu viruses and contains three times the antigen (the part of the vaccine that helps your body build up protection against flu viruses) than other standard-dose inactivated flu vaccines, to help create a stronger immune response.

An egg-based high-dose flu shot (Fluzone High-Dose Quadrivalent), which is approved for use in people 65 years and older. This vaccine contains four times the antigen (the part of the vaccine that helps your body build up protection against flu viruses) than other standard-dose inactivated flu vaccines, to help create a stronger immune response.

An egg-based adjuvanted flu shot (Fluad Quadrivalent), is approved for people 65 years and older. This vaccine is made with an adjuvant (an ingredient that helps create a stronger immune response).

An egg-based live attenuated flu nasal spray vaccine (FluMist Quadrivalent) made with attenuated (weakened) live flu viruses, which is approved for use in people 2 years through 49 years. This vaccine is not recommended for use in pregnant people, immunocompromised people, or people with certain medical conditions.

Are any of the available flu vaccines recommended over others?

Yes, for some people. For the 2022-2023 flu season, there are three flu vaccines that are preferentially recommended for people 65 years and older. These are the Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant  flu vaccine, and Fluad Quadrivalent adjuvanted flu vaccine. This recommendation was based on a review of available studies which suggests that, in this age group, these vaccines are potentially more effective than standard dose unadjuvanted flu vaccines. There is no preferential recommendation for people younger than 65 years.

If none of the three flu vaccines preferentially recommended for people 65 years and older is available at the time of administration, people in this age group should get any other age-appropriate flu vaccine instead.

Who Should Be Vaccinated?

Everyone 6 months and older in the United States should get an influenza (flu) vaccine every season with rare exception. CDC’s Advisory Committee on Immunization Practices has made this “universal” recommendation since the 2010-2011 flu season.

Vaccination to prevent flu and its potentially serious complications is particularly important for people who are at higher risk of developing serious flu complications. A full list of age and health factors that confer increased risk is available at People at Higher Risk of Developing Flu-Related Complications.

Who Should Not Be Vaccinated?

Different influenza (flu) vaccines are approved for use in people 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 the flu vaccine or its components. More information is available at Who Should and Who Should NOT get a Flu Vaccine.

When should I get vaccinated?

For most people who need only one dose of flu vaccine for the season, September and October are generally good times to be vaccinated against flu. Ideally, everyone should be vaccinated by the end of October. Additional considerations concerning the timing of vaccination for certain groups of people include:

Most adults, especially those 65 years and older, and pregnant people in the first or second trimester should generally not get vaccinated early (in July or August) because protection may decrease over time. However, early vaccination can be considered for any person who is unable to return at a later time to be vaccinated.

Some children need two doses of flu vaccine. For those children, it is recommended to get the first dose as soon as the vaccine is available because the second dose needs to be given at least four weeks after the first. Vaccination during July and August also can be considered for children who need only one dose.

Vaccination during July and August also can be considered for people who are in the third trimester of pregnancy during those months, because this can help protect their infants for the first few months after birth (when they are too young to be vaccinated).

Where can I get a flu vaccine?

Flu vaccines are offered in many doctors’ offices and clinics. 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, college health center, and even in some schools and workplaces.

Why do I need a flu vaccine every year?

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

Does the 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 (flu) vaccine effectiveness (VE) can vary. The protection provided by a flu vaccine varies from season to season and depends in part on the age and health status of the person getting the vaccine and the similarity or “match” between the viruses in the vaccine and those in circulation. During years when the flu vaccine match is good, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness and complications. However, the benefits of flu vaccination will still vary, depending on the characteristics of the person being vaccinated (for example, their health and age), what flu viruses are circulating that season, and, potentially, which type of flu vaccine was used.

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 four flu viruses that research suggests will be most common.

Unfortunately, some people can become infected with a flu virus that the vaccine is designed to protect against, despite getting vaccinated. The 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 some 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 virus infection.

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

Some people who get vaccinated may still get sick with the flu. However, flu vaccination has been shown in studies to reduce the severity of illness in people who get vaccinated but still get sick. A 2021 study showed that among adults, flu vaccination was associated with a 26% lower risk of ICU admission and a 31% lower risk of death from flu compared with those who were unvaccinated. 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.

Vaccine Benefits

Flu vaccination can keep you from getting sick with flu.

The flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.

During seasons when flu vaccine viruses are similar to circulating flu viruses, the flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.

Flu vaccination has been shown in several studies to reduce the severity of illness in people who get vaccinated but still get sick.

A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.

A 2018 study showed that among adults hospitalized with flu, vaccinated patients were 59% 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 four fewer days in the hospital than those who were not vaccinated.

Flu vaccination can reduce the risk of flu-associated hospitalization.

The flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 105,000 flu-related hospitalizations.

• A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
• A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40% on average.
• A 2014 study showed that flu vaccination reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu seasons from 2010-2012.
• Flu vaccination is an important preventive tool for people with certain chronic health conditions.
• Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
• Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
• Among people with diabetes and chronic lung disease, flu vaccination has been shown in separate studies to be associated with reduced hospitalizations from a worsening of their chronic condition.
• Flu vaccination during pregnancy helps protect pregnant people from flu during and after pregnancy and helps protect their infants from flu in their first few months of life.
• Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.
• A 2018 study showed that getting a flu shot reduced a pregnant person’s risk of being hospitalized with flu by an average of 40% from 2010-2016.
• A number of studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth when babies are too young to be vaccinated.
• Flu vaccines can be lifesaving in children.
• A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.
• A 2020 study found that during the 2018-2019 flu season, flu vaccination reduced flu-related hospitalization by 41% and flu-related emergency department visits by half among children (aged 6 months to 17 years old).
• A 2017 study was the first of its kind to show that flu vaccination can significantly reduce children’s risk of dying from flu.

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.

Despite the many benefits offered by flu vaccination, only about half of Americans get an annual flu vaccine. During an average flu season, flu can cause millions of illnesses, hundreds of thousands of hospitalizations, and tens of thousands of deaths. Many more people could be protected from flu if more people got vaccinated.