Researchers from the Perelman School of Medicine have developed a vaccine to protect against genital herpes. Tested on both mice and guinea pigs, the immunization led to “mostly sterilizing immunity” from the virus—the strongest type of immunity. The results of the study are published in Science Immunology.

In the study, researchers delivered the Penn-developed vaccine to 64 mice and then exposed them to genital herpes. After 28 days, 63 of the mice were found to have sterilizing immunity, meaning there was no trace of herpes infection or disease after the exposure. The one remaining mouse developed dormant infection without any prior genital disease. Similarly, 10 guinea pigs, which have responses to herpes infections that more closely resemble that of humans, were also given the vaccine and exposed to the virus. No animal developed genital lesions and only two showed any evidence that they became infected, but the infection was not in a form that animals could transmit the virus.

“We’re extremely encouraged by the substantial immunizing effect our vaccine had in these animal models,” says the study’s principal investigator Harvey Friedman, a professor of infectious diseases. “Based on these results, it is our hope that this vaccine could be translated into human studies to test both the safety and efficacy of our approach.”