Three reasons: Three reasons: 1. Influenza viruses mutate over time, 2. the virus strains circulating can vary year to year, and 3. our immunity wanes over time.
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Why does the flu vaccine have to be updated…
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Three reasons: Three reasons: 1. Influenza viruses mutate over time, 2. the virus strains circulating can vary year to year, and 3. our immunity wanes over time.