The primary response when a microorganism enters the body is described as natural active immunity. Vaccines close vaccineA substance that stimulates the body to produce antibodies to provide ...

A few are not immune, and they are ill and contagious. The result is that the majority are protected due to the high level of immunity. A few individuals will still become ill, but the large ...

"There's certainly preexisting immunity," says Florian Krammer, a virologist at Mount Sinai's Icahn School of Medicine who is involved in some of the new studies. "That's very likely not going to ...