The best way to prevent getting the flu and spreading it is to get a flu vaccine. The vaccine is also the best way to make flu symptoms less severe if you do get the flu. Everyone 6 months of age and older should get the vaccine every year. Certain groups of people should never miss getting a flu shot, since they may get more severe illness if they get the flu. (See the inset below.) Because it takes about 2 weeks for the vaccine to work completely, it is important to get vaccinated before the flu season starts (October through May). Most flu cases occur between January and February.
The influenza virus can change (or mutate) rapidly over time, letting it dodge the body’s immune system and cause illness. People can also lose immunity from previous vaccines over time. In order to overcome these issues, new flu vaccines are made every year based on predictions about which viruses will be most common during the next flu season. You should be vaccinated every year.