Question
List two important differences between live and killed polio virus vaccines.
Answer
Two important differences between live (OPV) and killed (IPV) polio vaccines:
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Type of immunity induced: OPV (live attenuated) induces both systemic (IgG) and local intestinal mucosal (secretory IgA) immunity — important for interrupting faecal-oral transmission, since it blocks intestinal replication/shedding of wild poliovirus on subsequent exposure; IPV (killed) induces only systemic (humoral) immunity, without significant mucosal IgA, so a vaccinated individual can still support intestinal replication and shed wild poliovirus if exposed, even while remaining protected from paralytic disease themselves.
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Risk of vaccine-associated paralytic poliomyelitis (VAPP): OPV carries a very rare but recognized risk of the live attenuated vaccine strain reverting to a more neurovirulent form, causing VAPP; IPV, being a killed vaccine with no live/replicating virus, carries no risk of VAPP.
(Other valid points: OPV is given orally, easier and cheaper for mass administration; IPV is given by injection, requiring trained personnel.)