Question

what is the best reason why people must be vaccinated once a year for influenza? multiple choice mutations cause antigenic drift in ha and na proteins. the amount of vaccine decreases in blood after one year. the vaccine is removed by the body after 12 months. the virus binds to all of the vaccine after a few months. the immune system only
emembers\ vaccines for several months.

Explanation:

Influenza viruses undergo mutations, leading to antigenic drift in their HA (hemagglutinin) and NA (neuraminidase) proteins. This means the virus's surface antigens change over time, so the previous vaccine may not be effective against the new mutated strain. The other options are incorrect: the vaccine doesn't just decrease or get removed in a year - the immune system can have memory, but the virus mutates. The virus binding to all vaccine is not accurate. So the best reason is due to antigenic drift from mutations.

Answer:

A. Mutations cause antigenic drift in HA and NA proteins.