Why must an influenza vaccine be given again before every new season?

1. Influenza has a high mutation rate compared with most other viruses and with normal host cells. 2. Those mutations fall on the surface molecules of the virus. 3. Changed surface molecules let the virus evade the protective immunity gained in a previous influenza season. 4. So the vaccine has to be remade and given again each year to match the circulating virus. 5. Measles, mumps and rubella viruses mutate so rarely that the same vaccine serves year after year, which is the contrast. 6. Nothing about influenza involves a genome switching between RNA and DNA, so that option is invented. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.3 Prevention and Treatment of Viral Infections_