“The preexisting immunity to human adenoviruses has really made that approach difficult, if not unworkable,” said Christopher Walker of Nationwide Children’s Hospital in Columbus, Ohio, who was not involved in the research. “I think that they have found a very nice way around that.”

Nicosia and his team found their alternative to human adenoviruses from a rather unpleasant source: chimp poop. Because of people’s similarity to chimps, Nicosia reasoned, adenoviruses that can infect chimps can probably infect humans as well. Importantly, however, they generally don’t, so people haven’t built up antibodies to the viruses.

Collecting stool samples from zoos and animal facilities, Nicosia and his team isolated and characterized almost 30 different chimp adenovirus serotypes from some 1,000 stool samples. They made safe forms of the viruses that were unable to replicate, and tested them for their immune potency in mice. The best ones, generating the biggest cellular immune responses, were chosen for making trial vaccines.