Which statement about OPV and mucosal immunity is true?

• A. OPV can induce mucosal immunity in the gut, contributing to reduced viral shedding.
• B. OPV does not affect mucosal immunity.
• C. IPV induces mucosal immunity more than OPV.
• D. Mucosal immunity is not relevant to polio.

Answer: (A)

The key idea is that mucosal immunity in the gut helps limit poliovirus replication where the virus first takes hold and reduces how much virus is shed, which in turn lowers transmission. The oral polio vaccine is live and taken by mouth, so it replicates in the gut and strongly stimulates mucosal defenses there, including secretory IgA. This mucosal response helps block intestinal replication of poliovirus and reduces viral shedding in stool, contributing to decreased spread. In contrast, the injectable inactivated polio vaccine mainly induces systemic antibodies and provides strong protection against paralysis but generates much weaker mucosal immunity in the gut, so its effect on gut replication and shedding is limited. Mucosal immunity matters for transmission, not just disease prevention, making the statement about OPV inducing gut mucosal immunity and reducing shedding the true one.