Influenza (Flu) is a respiratory infection that can cause serious complications, particularly to young children and to older adults. Flu shots are the most effective way to prevent influenza and its complications. The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months of age or older be vaccinated annually against influenza. Here are the answers to a common question about flu shots:

Why do I need to get vaccinated every year? New flu vaccines are released every year to keep up with rapidly adapting flu viruses. Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses.

After vaccination, your immune system produces antibodies that will protect you from the vaccine viruses. In general, though, antibody levels start to decline over time — another reason to get a flu shot every year.

It takes up to two weeks to build immunity after a flu shot, but you can benefit from the vaccine even if you don't get it until after flu season starts.