Seasonal Flu Shot

What is the flu shot?

The flu shot is a vaccine given with a needle, usually in the arm. The seasonal flu shot protects against the three or four influenza viruses that research indicates will be most common during the season.

Is there more than one type of flu shot available?

Yes.

There are many 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 2018-2019 flu season, and age indications for each vaccine are available in CDC’s Table: U.S. Influenza Vaccine Products for the 2018-19 Season.

Who should get vaccinated this season?

Who should not get a flu shot?

How effective is the flu shot?

What are the risks from getting a flu shot?

The risk of a flu shot causing serious harm or death is extremely small. However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions. 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 flu vaccine or any part of flu vaccine. Almost all people who get influenza vaccine have no serious problems from it. For more information, see Influenza (Flu) Vaccine Safety.

What are the side effects that could occur?

The most common side effects from the influenza shot are soreness, redness, and tenderness or swelling where the shot was given. Low-grade fever, headache and muscle aches also may occur.

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 flu vaccine or any part of flu vaccine.

There is a small possibility that influenza vaccine could be associated with Guillain-Barré syndrome, 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 influenza 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.

Can the flu shot give me the flu?

No, a flu shot cannot give you the flu. Flu vaccines that are administered with a needle are currently made in two ways: the vaccine is made either with a) flu vaccine viruses that have been ‘inactivated’ and are therefore not infectious, or b) with no flu vaccine viruses at all (which is the case for recombinant influenza vaccine). In randomized, blinded studies, where some people got flu shots and others got saltwater shots, the only differences in symptoms was increased soreness in the arm and redness at the injection site among people who got the flu shot. There were no differences in terms of body aches, fever, cough, runny nose or sore throat.

More information about these studies is available at:

• Carolyn Bridges et al. (2000). Effectiveness and cost-benefit of influenza vaccination of healthy working adults: A randomized controlled trial.
• Kristin Nichol et al. (1995). The effectiveness of vaccination against influenza in healthy working adults. New England Journal of Medicine. 333(14): 889-893.

Why do some people not feel well after getting the flu shot?

The flu shot can cause mild side effects that are sometimes mistaken for flu. For example, people sometimes experience a sore arm where the shot was given. The needle stick may also cause some soreness at the injection site. Rarely, people who get the flu shot have fever, muscle pain, and feelings of discomfort or weakness. If experienced at all, these effects usually last for 1-2 days after vaccination, and are much less severe than actual flu illness.

What about people who get a flu shot and still get sick with flu symptoms?

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:

1. 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.)
2. 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.
3. 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.

More Information:

• How Well Does the Seasonal Flu Vaccine Work?

What protection does the 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 flu patients. Another study in 2018 showed that a vaccinated adult who was hospitalized with flu was 59 percent less likely to be admitted to the Intensive Care Unit 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 4 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.