A vaccine is given to provide immunity against the virus that causes influenza. A different influenza vaccine is required each year because the virus changes by mutation regularly. What is the reason for needing a new influenza vaccine every year?
- AMemory cells become less effective as they age.
- BThe primary immune response does not produce enough antibodies.
- CThe secondary immune response does not produce enough antibodies.
- DThe virus antigens change and are not recognised by the immune system.