How Do Flu Shots Work?

Flu viruses change from year to year. Labs make a new flu vaccine (shot) to match the three-to-four strains, or types, of flu viruses that researchers predict will be the most common for the upcoming season. That’s why you need to get a flu shot every year.

A health care professional will give you the vaccine. It is most often given as a shot, or injection, into the muscle in your upper arm. After you get it, your body will develop antibodies to help you fight off the strains of the virus that the vaccine targets. It takes about two weeks for you to become protected.

There also is a nasal flu vaccine that is sprayed into your nose. Unlike the flu shot, the nasal flu vaccine contains live, but weakened virus, and may not be a good option for people with heart disease or other conditions.