Concerns about bird flu continue to grow as a new deadly subtype spreads among wild animals and livestock, but researchers at the University of Pennsylvania have begun work on an experimental mRNA vaccine against the virus. And it’s already showing promising preclinical results.

The H5N1 subtype of avian flu has spread among both poultry and cattle and has already infected three humans in the U.S. While the health risk to the general public remains low, according to health officials, and there are no sustained signs of human-to-human contact, officials are taking a cautious stance after the coronavirus pandemic—and researchers note that mRNA vaccines take less time to develop than traditional vaccines.

“The mRNA technology allows us to be much more agile in developing vaccines; we can start creating [an] mRNA vaccine within hours of sequencing a new viral strain with pandemic potential,” said Scott Hensley, a professor of microbiology at UPenn’s Perelman School of Medicine in a statement. “During previous influenza pandemics, like the 2009 H1N1 pandemic, vaccines were difficult to manufacture and did not become available until after the initial pandemic waves subsided.”

The vaccine that researchers are working on could help manage the outbreak of the virus in birds and cattle and prevent human interactions, UPenn said. In addition to the potential human threat, H5N1 represents a danger to both the livestock and poultry industries. Egg prices are on the rise once again because of bird flu, jumping 16% from January to late April. And the U.S. Department of Agriculture (USDA) has offered $98 million to the Animal and Plant Health Inspection Service to help livestock farmers slow the spread of the virus. 

To assist with its research, UPenn is consulting with immunologist Dr. Drew Weissman, cowinner of the 2023 Nobel Prize for his work that enabled the development of mRNA vaccines against COVID-19.

“Before 2020, experts thought the influenza virus posed the greatest risk of causing a pandemic, and we had limited options for creating a vaccine if that had happened,” said Weissman. “COVID-19 showed us the power of mRNA-based vaccines as a tool to protect humans from emerging viruses quickly, and we are better prepared now to respond to a variety of viruses with pandemic potential, including influenza.”

The researchers developed the vaccine for a specific subtype of H5N1 which is spreading among birds and cattle. That subtype rarely infects humans, but as COVID demonstrated, viruses often mutate and evolve—and some fear a mutation of this one could start a new pandemic.

Scientists at UPenn have so far tested the vaccine in mice and ferrets and found that those that received it maintained high levels of antibodies a year after vaccination. The vaccine also appeared to reduce symptoms in those who were infected. All the vaccinated animals survived infection from H5N1, while the unvaccinated mice and ferrets did not.

Traditional vaccines are generally egg-based, researchers say. Experts traditionally inject fertilized chicken eggs with what they predict will be the dominant viral strain, let it replicate, and then inactivate the virus to use in the flu shots distributed globally. That takes up to six months to develop, though; mRNA vaccines take much less time.

UPenn researchers say a comparison of the two types of vaccines shows the mRNA version was just as effective as the traditional one.

News of the mRNA vaccine trials come as the government has opted to fill just under 5 million vialed doses of bird flu vaccines into the national stockpile as a precaution. That process can take a couple of months.

H5N1 was first identified in 1997. To date, it has infected 900 humans, half of whom have died from the virus. (All of the recent people infected with the latest strain have recovered.)

More than 92 million poultry in 48 states have been affected by the virus, as have 63 dairy herds, according to the Centers for Disease Control and Prevention (CDC). The USDA has been inspecting cattle before slaughter to ensure they are fit to enter the human food supply. Officials at that agency say they are “confident that the meat supply is safe.” The FDA, meanwhile, says there is no reason to be concerned about pasteurized dairy products.