Influenza vaccine


An influenza vaccine protects you against the flu . A new form of the flu vaccine needs to be made each year to protect you against the exact strains that are expected to be most common.

Alternative Names

Vaccine - influenza; Immunization - influenza; Flu shot; Flu vaccine


The flu is a respiratory disease that spreads easily. It is caused by an influenza virus. Thousands of people in the U.S. die each year from the flu or its complications. Most of those who die are the elderly, young children, or people with weakened immune system.

2012-2013 VACCINE

There are two types of flu vaccines: a flu shot and a nasal spray.

  • The flu shot contains killed (inactive) viruses. So you cannot get the flu from this type of vaccine. Some people do get a low-grade fever for a day or two after the shot. The flu shot is approved for people age 6 months and older.
  • A high-dose version of the flu shot called Fluzone High Dose can be given to people 65 and older. At this time it is not known if the higher dose vaccine is better than the regular vaccine at protecting from the flu.
  • Flu shots may be injected into the muscle or just below the skin.
  • A nasal spray flu vaccine called FluMist uses live, weakened flu viruses instead of dead ones. The spray is approved for healthy people aged 2 through 49 who are not pregnant. It should not be used in those who have asthma or children under age 5 who have repeated wheezing episodes.

Flu vaccines are generally given at the beginning of the flu season. This is usually around October in the U.S. However, they may be given as late as March, and still provide some benefit.

People traveling to other countries should be aware that the flu may occur at different times of the year from the U.S.


The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months and older should receive the flu vaccine. Some people are more likely to get the flu or to have a severe infection if they catch it. People at risk of more serious flu infections should always get a flu vaccine every year. The CDC recommends extra effort to vaccinate the following people:

  • Pregnant women or women who will be pregnant during the flu season
  • Children younger than 5 years and especially those under 2 years (but 6 months or older)
  • Household contacts and caregivers of children under the age of 6 months, including breastfeeding women
  • Health care workers or those who live with a health care worker
  • People who have chronic lung or heart disease
  • People who have sickle cell anemia or other hemoglobinopathies
  • People who live in a nursing home or extended care facilities
  • People who live with someone who has chronic health problem
  • People who have kidney disease, anemia , severe asthma , diabetes , or chronic liver disease
  • People who have a weakened immune system (including those with cancer or HIV/AIDS)
  • People who take long-term treatment with steroids for any condition

Persons 9 years and older need a single flu shot each year. Children 6 months to 8 years old should get two shots at least 1 month apart if they are getting the flu vaccine for the first time. Be sure to ask your child’s doctor for more specific information.


Most people are protected from the flu about 2 weeks after receiving the vaccine.


Most people have no side effects from the flu shot. Soreness at the injection site or minor aches and low grade fever may be present for several days.

As is the case with any drug or vaccine, there is a rare possibility of allergic reaction.

The regular seasonal flu shot has been shown to be safe for pregnant women and their babies.

Normal side effects of the nasal spray flu vaccine include fever, headache, runny nose, vomiting, and some wheezing. Although these symptoms sound like symptoms of the flu, the side effects do not become a severe or life-threatening flu infection.


Some people should not be vaccinated without first talking to their doctor. The vaccine is not approved for people under 6 months of age. In general, you should not get a flu shot if you:

  • Had a severe allergic reaction to chickens or egg protein (most people with a mild egg allergy can receive the flu shot safely)
  • Have a fever or illness that is more than "just a cold"
  • Had a moderate to severe reaction after a previous flu vaccine
  • Developed Guillain-Barre syndrome within 6 weeks after receiving a flu vaccine

If any of the above applies to you, ask your doctor if a flu vaccine is safe for you.


Centers for Disease Control and Prevention (CDC). Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2012. . 2012 Aug 17;61(32):613-618.

Centers for Disease Control and Prevention. Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedule for Adults Aged 19 Years and Older-- United States, 2013. Available Accessed February 8, 2013.

Centers for Disease Control and Prevention. Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedule for Persons Aged 0 Through 18 Years-- United States, 2013. Available Accessed February 8, 2013.

Encyclopedia content is provided as information only and not intended to replace the advice and instruction from your personal physician.