Why annual influenza vaccination? — Choose the best reason people are advised to receive the flu vaccine each year.
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Amutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
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Bit is a polysaccharide vaccine that does not confer long-term protection
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Cthe vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
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Dnone of the above
Answer
Correct Answer: mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
Explanation
Introduction / Context:Influenza viruses evolve rapidly by antigenic drift, especially in the hemagglutinin surface glycoprotein that is the principal target of neutralizing antibodies. As a result, immune protection from prior infection or vaccination can diminish when circulating strains acquire new antigenic signatures. This underpins the policy of updating and administering influenza vaccines annually.
Given Data / Assumptions:
- We consider the typical inactivated or live-attenuated influenza vaccines.
- The immune correlate of protection is mainly antibodies against hemagglutinin.
- Vaccine composition changes to match predicted circulating strains.
Concept / Approach:Yearly vaccination addresses antigenic drift that alters epitopes on hemagglutinin (and neuraminidase). These mutations reduce binding of previously generated antibodies, decreasing neutralization. The vaccine is protein based, not a plain polysaccharide formulation, and modern vaccines are designed to be safe; dose limitations are not due to toxicity but to immunological formulation and manufacturing considerations.
Step-by-Step Solution:
Identify antigenic drift as the driver of immune escape year to year.Associate drift with hemagglutinin mutations that change antibody epitopes.Select the option that directly states this mechanism.Verification / Alternative check:Global surveillance networks update vaccine strain selections biannually for Northern and Southern Hemispheres, reflecting the need to keep pace with drifted strains.
Why Other Options Are Wrong:
- Polysaccharide vaccine: incorrect; influenza vaccines are not plain polysaccharide vaccines.
- Toxicity requiring small doses: incorrect; dosing is set for immunogenicity and safety, not because the product is inherently too toxic.
- None of the above: incorrect because the drift explanation is correct.
Common Pitfalls:Confusing antigenic drift with antigenic shift; shift produces pandemics but is less frequent than the seasonal drift that prompts annual vaccination.
Final Answer:mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines