New influenza vaccines are needed every few years because
- A. immunity produced by the vaccine lasts only days
- B. influenza virus infects only elderly people
- C. antibiotics destroy the vaccine
- D. the surface antigens of the virus mutate frequently
Explanation
Influenza's RNA genome mutates rapidly and its haemagglutinin and neuraminidase surface proteins keep changing, so last year's antibodies may not recognise this year's strain. This antigenic drift is the reason vaccination is reviewed every season.
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