Massachusetts Institute of Technology Jun 3 2026 In the United States, children routinely receive an injectable form of the polio vaccine. This vaccine is very effective at preventing illness, but it doesn't block transmission of the polio virus as well as the oral polio vaccine does. Poliovirus is usually transmitted through contaminated food or water, so the GI tract is where the body is first exposed. Because the oral vaccine induces a mucosal immune response within the GI tract, it is much