Influenza vaccine


An influenza vaccine can reduce the chance that you get ill with the flu and pass it on to others.

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 of the flu or its complications. Most of those who die are the elderly, young children, or people with a weakened immune system.

2013-2014 VACCINE

Each year the flu vaccine is made to protect against the strains of the flu virus that scientists expect to be most common. Talk with your health care provider about which of the following vaccines you should receive:

  • The trivalent vaccine, which protects against three flu virus strains
  • The quadrivalent vaccine, which protects against four flu virus strains

The flu vaccine comes in two forms: a flu shot and a nasal spray.Your health care provider can recommend which of the two forms you should receive.


  • 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 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.


  • The nasal spray flu vaccine uses live, weakened flu viruses instead of dead ones.
  • The spray is approved for healthy people aged 2 through 49 years.
  • It should not be used in those who have asthma or children under age 5 who have repeated wheezing episodes.
  • It should not be used in pregnant women.

Vaccines made without eggs are available for people who are allergic to eggs. These vaccines are called recombinant vaccines. Ask your health care provider if these are safe for you.


The flu vaccine should be received at the start of the flu season. This is around October in the U.S. The vaccine can be received as late as March and still provide some protection. People traveling to other countries should be aware that the flu may be more common 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 making an extra effort to vaccinate:

  • Pregnant women or women who will be pregnant during the flu season
  • Children 6 months to 5 years of age, especially those under 2 years of age
  • Household contacts and caregivers of children under the age of 6 months, including breastfeeding women
  • Health care workers and those who live with health care workers
  • People who have chronic lung or heart disease
  • People who have sickle cell anemia or other hemoglobinopathies
  • People living in a nursing home or extended care facilities
  • People living with someone who has chronic health problems
  • 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 vaccine. Soreness at the injection site, minor aches, or a 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.


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

  • 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.

If you are allergic to chickens or egg protein, ask your doctor if you can safely receive the recombinant vaccine, which is not made from chicken eggs.


Centers for Disease Control and Prevention (CDC). Summary Recommendations: Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP) United States, 2013-2014. Available at: Accessed September 26, 2013.

Review Date: 
Reviewed By: 
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.