Flu Shot: Influenza Vaccine and Side Effects
How does the flu shot or influenza vaccine work to prevent flu?
Flu shots and the nasal flu vaccine work by causing antibodies to develop in your body. These antibodies provide protection against infection from the flu virus. This antibody reaction may cause fatigue and muscle aches in some people.
Remember that the flu vaccine cannot cause the flu. Sometimes, people who get vaccinated during flu season catch the flu in the two weeks before the vaccine has a chance to fully work. While it's human nature to see a link between the two events, there's no medical evidence that flu vaccines cause flu or make people susceptible to flu. And even though flu vaccines are not 100% effective -- vaccinated people sometimes get flu infections -- vaccinated people almost always have milder flu than people who weren't vaccinated.
Each year, the flu vaccine contains several different kinds of the virus. The strains chosen are the ones that researchers determine are most likely to show up that year.
Who should get the flu shot?
An annual flu vaccination is recommended for everyone ages 6 months and older. It's particularly advised for high-risk individuals who are more prone to flu complications, such as pneumonia. Those at higher risk for complications include:
- Children younger than age 5, but especially those younger than 2 years old
- People age 65 years or older
- Women who will be pregnant during the flu season
- People who live in nursing homes
- Anyone with chronic heart or lung conditions, including asthma, or with any condition that weakens the immune system, such as diabetes or HIV
- Household caregivers -- including baby sitters -- of any children younger than age 5. This is particularly important for household caregivers of infants younger than age 6 months. (These children are too young to receive the flu vaccine.)
- Any person in close contact with someone in a high-risk group, such as health care workers and household contacts
To learn more about why all children should receive the flu vaccine, watch CDC's video Children Lost to the Flu. You may also want to visit the Families Fighting Flu web site.
Who should talk to their doctors before getting a flu shot?
According to the CDC, you should talk to your doctor before getting a flu shot or influenza vaccine if:
- You have had an allergic reaction to a flu shot in the past
- You have previously had Guillain-Barre syndrome that occurred after receiving the influenza vaccine; Guillain-Barre syndrome is a disorder in which the body's immune system attacks part of the nervous system.
- You are ill; if you have a fever, talk to your health care provider about getting the shot later. If you have a mild illness with no fever, it's OK to get a flu shot.
It's long been advised that people with allergies to eggs should not get the flu shot. However, the American College of Allergy, Asthma and Immunology says the vaccine contains such a low amount of egg protein that it's unlikely to cause an allergic reaction in those with an egg allergy. If you have a severe egg allergy (anaphylaxis), talk to your doctor before getting the flu vaccine. Also, as mentioned above, a flu vaccine that is not made with the use of eggs is available. The vaccine, called Flublok, is approved for use in those ages 18 to 49.