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How does the oral poliovirus vaccine strengthen immunity in the intestine?

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Polio vaccine — polio A health care worker giving a polio vaccine to a child in Katsina state, Nigeria, 2014.

The oral poliovirus vaccine (OPV), also known as the Sabin vaccine, strengthens immunity in the intestine because it consists of live but weakened (attenuated) poliovirus.1

When the vaccine is administered orally, the attenuated virus multiplies within the small intestine and associated lymph nodes. This replication process stimulates both systemic and local immune responses, which helps to boost immunity directly in the intestines. By generating antibodies against the wild virus in the gut, the vaccine effectively helps to stop the spread of the virus.12