How does IPV work to prevent poliovirus infection?

• A. It stimulates cellular immunity that clears infected neurons.
• B. It directly neutralizes the virus in the gut to stop intestinal replication.
• C. It induces strong intestinal immunity that blocks replication in the intestines.
• D. It produces protective antibodies in the blood, preventing the spread of poliovirus to the CNS.

Answer: (D)

The main idea is that the inactivated polio vaccine works by raising antibodies in the blood that neutralize poliovirus, so the virus cannot reach or damage the nervous system. After infection starts in the gut, circulating neutralizing antibodies bind the virus in the bloodstream and prevent viremia, which stops the virus from invading the central nervous system and causing paralysis. Intramuscular IPV mainly induces serum IgG, giving strong protection against CNS involvement, but it doesn’t generate as robust intestinal (m mucosal) immunity as the oral vaccine does. That’s why this option is the best fit: protective antibodies in the blood prevent the spread of poliovirus to the CNS. The other ideas aren’t the primary action of IPV—cellular immunity in neurons isn’t the main mechanism, IPV doesn’t directly neutralize virus in the gut to stop intestinal replication, and it doesn’t rely on strong intestinal immunity to prevent infection.