Why is a new influenza vaccine developed each year?

• A. Because influenza viruses are resistant to all vaccines after one year.
• B. Because the influenza virus undergoes frequent genetic mutations, leading to new strains.
• C. Because the previous year's vaccine becomes toxic over time.
• D. Because the immune system forgets how to respond to the virus after a year.

Answer: (B)

Verified step by step guidance

1. Understand that influenza viruses have a high mutation rate, especially in the genes encoding surface proteins like hemagglutinin (HA) and neuraminidase (NA).
2. Recognize that these frequent genetic changes are called antigenic drift, which results in new virus strains that can evade the immune response generated by previous vaccines.
3. Know that because of antigenic drift, the immune system may not recognize the new strains effectively, reducing the vaccine's protective effect over time.
4. Realize that to maintain effective immunity in the population, the influenza vaccine composition is reviewed and updated annually to match the most currently circulating strains.
5. Conclude that the need for a new influenza vaccine each year is due to the virus's rapid genetic mutations, not because of vaccine toxicity, immune system memory loss, or complete resistance after one year.