OPV interrupts transmission mainly through immunity in which part of the body?

• A. The intestines (mucosal immunity)
• B. Blood plasma
• C. Muscles
• D. Brain

Answer: (A)

OPV interrupts transmission mainly by inducing immunity in the gut lining, i.e., mucosal immunity in the intestines. When the oral vaccine infects cells in the intestinal mucosa, it stimulates secretory IgA and other local immune responses that limit poliovirus replication in the gut. Fewer viruses are shed in stool, which reduces fecal-oral transmission in the community. This gut-focused immunity is what makes OPV effective at stopping spread.

In contrast, systemic antibodies in the blood protect mainly against disease in the individual but don’t as effectively prevent gut replication and shedding. Immmunity in muscles or brain isn’t the mechanism by which transmission is controlled—the virus is shed from the gut, not from those tissues.