What is a flu vaccine?
Influenza (flu) vaccines (often called “flu shots”) are vaccines that protect against the four influenza viruses that research indicates will be most common during the upcoming season. Most flu vaccines are “flu shots” given with a needle, usually in the arm, but there also is a nasal spray flu vaccine.
The composition of flu vaccines has been updated for the 2023-2024 flu season.
Is there more than one type of flu shot available?
Yes. There are different flu vaccine manufacturers and multiple flu vaccines that are licensed and recommended for use in the United States. Fluzone High-DoseQuadrivalent vaccine,Flublok Quadrivalent recombinantflu vaccine andFluad Quadrivalent adjuvanted flu vaccine.
There are many flu vaccine options to choose from, but the most important thing is for all people 6 months and older to get a flu 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 flu vaccines for the current flu season, and age indications for each vaccine are available in CDC’s Table: U.S. Influenza Vaccine Products for the 2023-2024 Season.
Everyone 6 months and older in the United States, with rare exception, should get an influenza (flu) vaccine every season. CDC’s Advisory Committee on Immunization Practices has made this “universal” recommendation since the 2010-2011 influenza season.
Vaccination to prevent influenza and its potentially serious complications is particularly important for people who are at higher risk of developing serious influenza complications. A full list of age and health factors that are associated with increased risk is available at People at Higher Risk of Developing Flu-Related Complications.
More information is available at Who Needs a Flu Vaccine.
Different influenza 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 influenza vaccine or its components. More information is available at Who Should and Who Should NOT get a Flu Vaccine.
Yes, for some people. There are three flu vaccines that are preferentially recommended for people 65 years and older. These are Fluzone High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine or Fluad Quadrivalent adjuvanted flu vaccine. On June 22, 2022, CDC’s Advisory Committee on Immunization Practices (ACIP) voted unanimously to preferentially recommend these vaccines over standard-dose unadjuvanted flu vaccines. 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.
On This Page
- What is a flu vaccine?
- Is there more than one type of flu shot available?
- Who should and who should not get an influenza vaccine?
- Are any of the available flu vaccines recommended over others?
- What if a preferentially recommended flu vaccine is not available?
- How effective is the seasonal flu shot?
- What are the side effects that could occur?
- Can severe problems occur?
- What should I do if I have had a serious reaction to seasonal influenza vaccine?
- Why do some people not feel well after getting the flu shot?
- What about people who get a seasonal flu vaccine and still get sick with flu symptoms?
- What protection does the flu vaccine provide if I do get sick with flu?
- Recommendations for Vaccination of People with Egg Allergy
- Vaccine Information Statements (VIS)
Vaccine Information Statements (VIS)
Flu VISs are no longer updated every year. The edition dated 8/15/2019 should be used for the current flu season.
Several formats including PDF available.
Access VIS Here
If one of the three preferentially recommended flu vaccines for people 65 and older is not available at the time of administration, people in this age group should get an age-appropriate standard-dose flu vaccine instead.
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 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. More information is available atVaccine Effectiveness – How well does the Flu Vaccine Work.
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 2019-2020, the last flu season prior to the COVID-19 pandemic, flu vaccination prevented an estimated 7 million influenza illnesses, 3 million influenza-associated medical visits, 100,000 influenza-associated hospitalizations, and 7,000 influenza-associated deaths.
- During seasons when 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% to 60%.
- Flu vaccination has been shown in several studies to reduce 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.
- Flu vaccine prevents tens of thousands of hospitalizations each year. For example, during 2019-2020 flu vaccination prevented an estimated 100,000 flu-related hospitalizations.
- A 2018 studyshowed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an ICU with flu by 82%.
- A 2017 systematic review found that during 2010-2011 through 2014-2015, 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 helpsprotect pregnant people from flu during and after pregnancyand helps protect their infants from flu in their first few months of life.
- A2013 studyshowed that during the 2010–2011 and 2011–2012 flu seasons vaccination reduced the risk of flu-associated acute respiratory infection in pregnant people by aboutone-half.
- A2018 studyshowed 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 studieshave 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 vaccine 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 studywas 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.
*References for the studies listed above can be found at Publications on Influenza Vaccine Benefits.
What are the side effects that could occur?
Common side effects from a flu shot include soreness, redness, and/or swelling where the shot was given, headache (low grade), fever, nausea, muscle aches, and fatigue. The flu shot, like other injections, can occasionally cause fainting.
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Can severe problems occur?
Life-threatening allergic reactions to flu shots are very rare. Signs of serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness. If they do occur, it is usually within a few minutes to a few hours after receiving the shot. These reactions can occur among persons who are allergic to something that is in the vaccine, such as egg protein or other ingredients. While severe reactions are uncommon, you should let your doctor, nurse, clinic, or pharmacist know if you have a history of allergy or severe reaction to influenza vaccine or any part of flu vaccine.
There is a small possibility that flu vaccine could be associated with Guillain-Barré syndrome, generally no more than 1 or 2 cases per million people vaccinated. This is much lower than the risk of severe complications from flu, which can be prevented by flu vaccine.
What should I do if I have had a serious reaction to seasonal flu vaccine?
Call a doctor or get to a doctor right away.
Tell your doctor what happened, the date and time it happened, and when you got the flu shot.
Ask your doctor, nurse, or health department to file a Vaccine Adverse Event Reporting System(VAERS) form, or call VAERS at 1-800-822-7967.Reports are welcome from all concerned individuals: patients, parents, health care providers, pharmacists and vaccine manufacturers.
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Why do some people not feel well after getting a flu shot?
Flu vaccine side effects are generally mild and go away on their own within a few days. Some side effects that may occur from a flu shot include soreness, redness, and/or swelling where the shot was given, headache (low grade), fever, nausea, muscle aches, and fatigue. The flu shot, like other injections, can occasionally cause fainting.
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There are several reasons why someone might get flu symptoms even after they have been vaccinated against flu.
- Someone can get sick with another respiratory virus besides flu such as rhinoviruses or SARS-CoV-2 (the virus that causes COVID-19). Other respiratory viruses can cause symptoms similar to flu, and they can also spread and cause illness during flu season. Flu vaccines only protect against flu, not other illnesses.
- Someone can be exposed to flu viruses shortly before getting vaccinated or during the two-week period after vaccination that it takes the body to develop immune protection. This exposure may result in a person becoming sick with flu before protection from vaccination takes effect.
- Flu vaccines vary in how well they work, and someone can get vaccinated but still get sick with flu. There are many different flu viruses that spread and cause illness among people, so this can happen if someone is exposed to a flu virus that is very different from the viruses in the flu vaccine. The ability of a flu vaccine to protect a person depends partially on the similarity or “match” between the vaccine viruses chosen to make vaccine and those spreading and causing illness. Even when that happens though, flu vaccination can still reduce severity of illness.
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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 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.
- Another study in 2018 showed that a vaccinated adult who was hospitalized with flu was 59% less likely to be admitted to an intensive care unit (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.
In addition, it’s important to remember that flu vaccine protects against three or four different viruses and multiple viruses usually circulate during any one season. 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.
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People with egg allergy may get any vaccine (egg-based or non-egg-based) that is otherwise appropriate for their age and health status. Previously, it was recommended that people with severe allergy to egg (those who have had any symptom other than hives with egg exposure) be vaccinated in an inpatient or outpatient medical setting. Beginning with the 2023-2024 season, additional safety measures are no longer recommended for flu vaccination of people with an egg allergy beyond those recommended for receipt of any vaccine, regardless of the severity of previous reaction to egg. All vaccines should be given in settings where allergic reactions can be recognized and treated quickly.
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