An experimental COVID-19 vaccine in pill form could be a win-win, as it not only protects against infection but also limits the airborne spread of the virus, tests in lab animals show.

The current vaccines reduce the risk of serious COVID-19 illness and hospitalization but aren't foolproof armor against infection with SARS-CoV-2.

"Considering most of the world is under-immunized — and this is especially true of children — the possibility that a vaccinated person with a breakthrough infection can spread COVID to unimmunized family or community members poses a public health risk," said study leader Stephanie Langel, of Duke University in Durham, N.C.

"There would be a substantial benefit to develop vaccines that not only protect against disease, but also reduce transmission to unvaccinated people," Langel said in a university news release.

In tests with hamsters, the vaccine prompted a strong antibody response in blood and the lungs. When the animals were exposed to SARS-CoV-2 at high levels and developed breakthrough infections, they were less symptomatic than non-vaccinated hamsters.

The vaccinated hamsters also had lower amounts of infectious virus in the nose and lungs, so they did not shed as much virus through normal airborne exposures, according to the study.

The findings were published May 5 in the journal Science Translational Medicine.

The vaccine uses an adenovirus as a vector to express the spike protein of the SARS-CoV-2 virus, the study authors explained.

Unlike vaccines injected into the muscle, the experimental vaccine seeks to neutralize the coronavirus by increasing production of immunoglobulin A (IgA) — the immune system's first line of defense against pathogens — in mucosal tissue in the nose and lungs.

Protecting these locations makes it less likely that vaccinated people will transmit infectious virus during a sneeze or cough, according to the researchers.

"Our data demonstrate that mucosal immunization is a viable strategy to decrease the spread of COVID through airborne transmission," Langel said.

This study focused on the original version of the coronavirus. Future studies will test the vaccine against omicron variants, Langel said. Whether results obtained in the animal studies can be replicated in humans also remains to be seen.

The research included teams from the vaccine developer, Vaxart, and a clinical research nonprofit called the Lovelace Biomedical Research Institute in Albuquerque, N.M.