The active strain changes from year to year. A new vaccine is made each year for the strains expected to dominate during the winter months. Because the viruses change frequently, and because protection from the vaccine lasts for only a few months, people who are at risk should get flu shots every year. Flu shots are given at most public health departments and doctors' offices. It is best to get a flu shot in the fall, before influenza season begins.
Flu vaccine contains no live virus, and only parts of killed virus.
The vaccine boosts immune responses against influenza. People may still get flu after being vaccinated, but they will usually have a less severe case than if they had not been vaccinated. The best way to prevent the flu is to get a flu shot each year. In addition, wash your hands frequently, and avoid rubbing your eyes or nose to prevent infection. If you do get flu, get plenty of rest, and drink lots of liquids to avoid becoming dehydrated.