Why do doctors suggest that people get a flu vaccine each year?

• A. Viruses can mutate from year to year.
• B. Viruses replicate more rapidly over time.
• C. Vaccines are absorbed by the body after a year.
• D. Vaccines get stronger over time.

Answer: (A)

The main idea is that influenza viruses mutate from season to season, so vaccines are updated each year to match the strains scientists expect to be circulating. As the virus copies itself, changes occur on its surface proteins, which can let new strains slip past immunity built from previous years. An updated vaccine presents your immune system with the right targets for the upcoming flu season, helping it respond quickly if you’re exposed. The other ideas aren’t accurate: vaccines don’t simply get stronger with time, aren’t kept in your body for a year, and the reason for annual shots isn’t that the virus just starts replicating faster over time.