Question

Why is there a need to be vaccinated with a new flu shot every year?

1) The RNA genome of influenza mutates frequently, causing minor changes. This is referred to as antigenic drift.
2) Influenza viruses may undergo a major genetic reassortment that dramatically changes HA and NA spikes, called antigenic shift.
3) The vaccine composition is not altered from year to year.
4) The flu vaccine confers lifelong immunity.

Answer 1

Annual flu shots are necessary due to the high mutation rates of influenza viruses, involving antigenic drift and shift that produce new strains not covered by the previous year's vaccine.

Step-by-step explanation:

Influenza viruses mutate frequently, resulting in minor changes known as antigenic drift. Additionally, they can undergo major genetic reassortment, known as antigenic shift. These constant changes in the influenza virus strains make it necessary to receive a new flu shot every year.

The need for an annual flu shot is primarily due to the high rates of antigenic variation in influenza viruses. Antigenic drift, a process involving frequent minor changes in the RNA genome of the influenza virus, and antigenic shift, a significant genetic reassortment resulting in changes to the virus's surface proteins, both contribute to the emergence of new flu strains against which the previous year's vaccine may not offer protection. Hence, the vaccine composition needs to be updated annually to include the most prevalent and predicted strains to maintain effective immunity in the population.