Can transmissible vaccines have a major role in eradicating disease?

Vaccines are powerful, but they are not perfect. In some cases, communities struggle to vaccinate enough individuals to stop the spread of a pathogen.

But suppose that instead of vaccinating most of a population, it were possible to vaccinate just a few individuals. In theory, a benign yet infectious vaccine could effortlessly and silently pass protection from one individual to another.

In a new mathematical model, researchers demonstrate that a weakly transmissible vaccine significantly lowers the incidence of infectious disease and paves the way toward eradication. The work was published October 26th in the journal Proceedings of the Royal Society B.

Researchers have long been interested in the idea of transmissible vaccines, and the idea has becoming increasingly viable over the last five years, says Leor Weinberger, a virologist at the University of California, San Francisco, and the Gladstone Institutes, who was not involved in the research. For example, several recombinant, transmissible vaccines are in development for wild animal populations, including one to protect wild rabbits against a fatal viral infection and another to prevent deer mice from carrying a virus responsible for a deadly human pulmonary disease.

But any discussion about a transmissible vaccine ultimately comes down to risk—in particular, the risk of the vaccine reverting to a pathogenic virus. This occurred accidentally with the oral polio vaccine in the early 1960s and again in the 2000s: On a few, rare occasions, the vaccine—a live, attenuated strain of poliovirus—reverted to virulent, neuron-attacking strains of the virus and caused polio infections.