**Vaccines** work by:
AKilling pathogens already in the body
BIntroducing antigens (killed/attenuated pathogens or their parts) to trigger primary immune response → memory cells → faster response on real infection
CProviding ready antibodies
DSuppressing the immune system
Answer & Solution
Correct answer: B. Introducing antigens (killed/attenuated pathogens or their parts) to trigger primary immune response → memory cells → faster response on real infection
Vaccination triggers active immunity: antigens stimulate B/T-cell response and memory cell formation. Upon real infection, memory cells launch a faster, stronger secondary response. Types: live-attenuated (MMR), inactivated (polio Salk), subunit (Hep B), toxoid (tetanus), mRNA (COVID).
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