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Why does the oral Sabin polio vaccine produce intestinal immunity?

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Infographic showing estimated lives saved by childhood vaccinations worldwide from 1974 to 2024, with syringe-shaped bars for each disease. Measles tops the list at 93.71 million lives saved, followed by tetanus, whooping cough, and others, for a total of 153.84 million lives saved. — vaccine Vaccines and the estimates of lives saved over the period 1974–2024.

The oral Sabin vaccine (OPV) produces intestinal immunity because it contains live, attenuated (weakened) poliovirus that is administered orally. Once swallowed, the virus replicates within the small intestine and associated lymph nodes.1

This replication process stimulates both systemic and local immune responses, which enhances overall protection against the virus. By inducing this local response in the gut, the vaccine effectively creates a barrier that can help prevent the virus from establishing an infection in the digestive tract, which is the primary site of entry for wild poliovirus.1