The main reason OPV can rapidly stop wild poliovirus transmission is because it induces what in the intestines?

• A. It induces a local immune response in the intestines.
• B. It creates systemic immunity only.
• C. It prevents infection by blocking replication in the bloodstream.
• D. It has no effect on transmission.

Answer: (A)

The important idea is that stopping transmission relies on mucosal immunity in the gut. OPV, being a live attenuated vaccine, replicates in the intestinal tract and stimulates a strong local immune response there, especially secretory IgA and gut-associated immune cells. This intestinal immunity limits how well the poliovirus can replicate in the gut, which reduces viral shedding in stool. Because poliovirus spreads mainly through fecal-oral transmission, less shedding means fewer opportunities for the virus to spread, rapidly interrupting transmission chains. Systemic immunity helps prevent disease but doesn’t prevent gut replication and shedding as effectively. Blocking replication in the bloodstream isn’t the main mechanism of transmission, and saying it has no effect on transmission isn’t accurate.