Compared with OPV, IPV induces very low levels of immunity in which part of the body?

• A. Lungs
• B. Blood
• C. Brain
• D. Intestines

Answer: (D)

Poliovirus first replicates in the gut, and the most relevant protection to prevent spread is mucosal immunity in the intestines. The oral polio vaccine is a live, replicating vaccine that stays in the gut and actively stimulates the intestinal mucosa, producing secretory IgA and other local defenses. This robust mucosal response helps block replication and shedding of the virus in the intestines, reducing transmission.

In contrast, the inactivated polio vaccine is given by injection and mainly boosts circulating antibodies in the blood. Those systemic antibodies protect against paralysis by preventing the virus from reaching the nervous system, but they don’t reliably induce strong gut mucosal immunity. That’s why immunity in the intestines is very low with IPV compared to OPV.

So the correct site where IPV induces very low immunity relative to OPV is the intestines; the other sites (lungs, blood, brain) are either not the primary battleground for mucosal defense or are already well-covered by the systemic immunity IPV provides.