Researchers at the University of Pittsburgh School of Public Health and the Center for Vaccine Research found that an experimental Rift Valley fever virus (RVFV) vaccine safely protected pregnant rats from severe disease and prevented infection in their offspring, marking an important step toward developing vaccines against one of the world’s most dangerous mosquito-borne viruses.
RVFV is a mosquito-borne virus found primarily in Africa and the Middle East that causes severe disease in livestock and can also infect humans. While many human infections are mild, the virus can cause pregnancy loss and severe complications, including blindness, liver disease and encephalitis. Because mosquitoes capable of carrying RVFV are found around the world, preventing its spread remains a global public health priority.
Published in June 2026 in mBio—a journal of the American Society for Microbiology—the study found that maternal vaccination with a live-attenuated RVFV vaccine generated strong antibody responses, prevented lethal maternal disease and blocked transmission of the virus to the fetus.
“We also initially wondered if pregnancy would suppress or negatively affect the immune response, but the pregnant animals mounted a perfectly fine response,” said Amy Hartman, PhD, associate professor of infectious diseases and microbiology at Pitt Public Health and a member of the Center for Vaccine Research. “Additionally, the vaccine proved to be completely safe. When using a live-attenuated vaccine, you always want to ensure the vaccine itself won’t cause any deleterious effects during pregnancy, and we didn’t find any.”
To evaluate the vaccine, researchers vaccinated pregnant rats with a live-attenuated RVFV vaccine candidate before exposing them to the virus. They also tested whether vaccination before pregnancy provided lasting protection during a later pregnancy by measuring antibody responses and evaluating whether vaccinated mothers and their fetuses were protected from infection.
Prior to this work, studies evaluating RVF vaccines during pregnancy were difficult because researchers lacked a practical animal model. Hartman’s laboratory developed a pregnant rat model in 2018, allowing scientists to study how the virus and potential vaccines affect both mothers and fetuses while providing a more accessible alternative to livestock models.
“The most striking finding was just how protective this vaccine actually was,” said Austin Hertel, a PhD student in the Program in Microbiology and Immunology at the School of Medicine. “About 50% of unvaccinated rats will succumb to the disease if infected during pregnancy. However, when they received the vaccine during pregnancy, 100% of them were protected. Furthermore, their offspring were born alive and healthy.”
Next, the team plans to study how long vaccine-induced protection lasts and apply the pregnancy model to evaluate additional vaccine platforms.
“We are excited to apply this blueprint for evaluating Rift Valley fever vaccines, as well as what we’ve learned from generating a pregnancy-specific data model, to other vaccine platforms that might have an even higher safety profile for pregnancy, such as mRNA- or protein-based platforms,” Hertel said.
Other authors of the study include Cynthia M. McMillen, Ryan M. Hoehl, Zachary D. Frey and Anita K. McElroy, all of the University of Pittsburgh.
-Ava Dzurenda