The virus rapidly multiplies there, jolting the immune system to produce a type of antibodies that are specific to mucosa, the moist tissue lining the nose, mouth, lungs and stomach. If the same person is exposed to the virus a second time, those antibodies, as well as immune cells that remember the virus, rapidly shut down the virus in the nose before it gets a chance to take hold elsewhere in the body. This is why mucosal vaccines, like the nasal spray FluMist or the oral polio vaccine, are better than intramuscular injections at fending off respiratory viruses, experts said. 