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FACT SHEET

Key Facts About Seasonal Flu Vaccine 

The single best way to protect against the flu is to get vaccinated each year.

There are two types of vaccines: 

• The "flu shot"— an inactivated vaccine (containing killed virus) that is given with a needle, 

usually in the arm. The flu shot is approved for use in people older than 6 months, including 

healthy people and people with chronic medical conditions.

• The nasal-spray flu vaccine — a vaccine made with live, weakened flu viruses that do not 

cause the flu (sometimes called LAIV for “live attenuated influenza vaccine” or FluMist®). LAIV 

(FluMist®) is approved for use in healthy* people 2-49 years of age who are not pregnant. 

Each vaccine contains three influenza viruses-one A (H3N2) virus, one A (H1N1) virus, and one B 

virus. The viruses in the vaccine change each year based on international surveillance and 

scientists' estimations about which types and strains of viruses will circulate in a given year. 

About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection 

develop in the body. 

When to Get Vaccinated

Yearly flu vaccination should begin in September or as soon as vaccine is available and continue 

throughout the influenza season, into December, January, and beyond. This is because the timing 

and duration of influenza seasons vary. While influenza outbreaks can happen as early as 

October, most of the time influenza activity peaks in January or later. 

Who Should Get Vaccinated

In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. However, 

it is recommended by ACIP that certain people should get vaccinated each year. They are either 

people who are at high risk of having serious flu complications or people who live with or care for 

those at high risk for serious complications. During flu seasons when vaccine supplies are limited or 

delayed, ACIP makes recommendations regarding priority groups for vaccination. 

People who should get vaccinated each year are: 

1. People at high risk for complications from the flu, including: 

• Children aged 6 months until their 5th birthday, 

• Pregnant women, 

• People 50 years of age and older, 
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• People of any age with certain chronic medical conditions, and 

• People who live in nursing homes and other long-term care facilities. 

2. People who live with or care for those at high risk for complications from flu, including: 

• Household contacts of persons at high risk for complications from the flu (see above), 

• Household contacts and out-of-home caregivers of children less than 6 months of age (these 

children are too young to be vaccinated), and 

• Health care workers. 

3. Children aged 6 months up to their 19th birthday

Use of the Nasal Spray Flu Vaccine

It should be noted that vaccination with the nasal-spray flu vaccine is always an option for healthy* 

people 2-49 years of age who are not pregnant. 

Who Should Not Be Vaccinated

There are some people who should not be vaccinated without first consulting a physician. These 

include 

• People who have a severe allergy to chicken eggs. 

• People who have had a severe reaction to an influenza vaccination. 

• People who have developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an 

influenza vaccine. 

• Children less than 6 months of age (influenza vaccine is not approved for this age group), 

and 

• People who have a moderate-to-severe illness with a fever (they should wait until they 

recover to get vaccinated). 

Vaccine Effectiveness

The ability of flu vaccine to protect a person depends on the age and health status of the person 

getting the vaccine, and the similarity or "match" between the virus strains in the vaccine and those in 

circulation. Testing has shown that both the flu shot and the nasal-spray vaccine are effective at 

preventing the flu. 

Vaccine Side Effects (What to Expect)

Different side effects can be associated with the flu shot and LAIV. 

The flu shot: The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu 

shot. Some minor side effects that could occur are: 

• Soreness, redness, or swelling where the shot was given 

• Fever (low grade) 

• Aches 

If these problems occur, they begin soon after the shot and usually last 1 to 2 days. Almost all 

people who receive influenza vaccine have no serious problems from it. However, on rare 
occasions, flu vaccination can cause serious problems, such as severe allergic reactions. As of July 

1, 2005, people who think that they have been injured by the flu shot can file a claim for 

compensation from the National Vaccine Injury Compensation Program (VICP). 

LAIV (FluMist®): The viruses in the nasal-spray vaccine are weakened and do not cause severe 

symptoms often associated with influenza illness. (In clinical studies, transmission of vaccine 

viruses to close contacts has occurred only rarely.) 

In children, side effects from LAIV (FluMist®) can include 

• runny nose 

• wheezing 

• headache 

• vomiting 

• muscle aches 

• fever 

In adults, side effects from LAIV (FluMist®) can include 

• runny nose 

• headache 

• sore throat 

• cough 

More Information 

• Flu Shot : Vaccination Information Statement (VIS) 

• Nasal Spray : Vaccination Information Statement (VIS)

* "Healthy" indicates persons who do not have an underlying medical condition that predisposes 

them to influenza complications.

For more information, visit www.cdc.gov/flu, or call CDC at 

800-CDC-INFO (English and Spanish) or 888-232-6348 (TTY). 

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