Study: mRNA Vaccine Provides Better Rotavirus Protection in Foals

Rotavirus, a leading cause of diarrhea in foals, poses significant health risks from gastrointestinal upset to death, despite the availability of vaccines. Researchers at Texas A&M University, in College Station, along with scientists in
clinicians from other Texas institutions, recently studied an experimental mRNA-based vaccine that could offer better protection for foals.
Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM-LA, distinguished professor and associate department head at Texas A&M’s College of Veterinary Medicine and Biomedical Sciences, presented the group’s findings at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida.
Understanding Equine Rotavirus Groups
Two distinct rotavirus groups cause diarrhea in foals: the long-recognized equine Group A rotavirus—ERVA, the microbe most frequently identified as a cause of diarrhea in foals—and the recently identified Group B rotavirus (ERVB) emerging in Central Kentucky, said Cohen. “While current vaccines, including the VP8 mRNA vaccine, target ERVA, they are not expected to protect against ERVB.”
Current Rotavirus Vaccine Limitations
In the U.S., veterinarians administer the existing rotavirus vaccine to pregnant mares in hopes of passing antibodies to foals at birth via colostrum, the first milk produced by the mare. “This killed virus vaccine has been the standard for decades, but its efficacy is increasingly questioned,” said Cohen.
In a recent study in Central Kentucky, researchers revealed that 83% of foals infected with either rotavirus strain were born to vaccinated mares, pushing veterinarians and scientists to seek more effective solutions, he added. Targeting the VP8 protein of ERVA—which acts as a surface spike protein responsible for attaching the virus to host cells—for vaccine development has shown promise in neutralizing the virus in humans, so Cohen’s team investigated its potential for equine applications.
Studying the New Rotavirus Vaccine
The researchers tested an mRNA-based vaccine targeting VP8 alongside the traditional vaccines in a controlled study involving 12 multiparous (having had more than one foal) mares and their foals. They divided the mares into four groups, receiving either one of the vaccines or no immunization (controls). They took blood samples before and after vaccination for the mares and on Days 1, 35, and 49 of life for foals.
Key Findings
- Mares:
- Antibody levels in all groups were similar prior to vaccination.
- The team observed a significant antibody increase post-vaccination only in the mares receiving the mRNA vaccine.
- Foals:
- On Day 1, after colostrum intake, foals of mRNA-vaccinated mares exhibited significantly higher antibody levels than those in other groups.
- By Day 49, foals of mRNA-vaccinated mares maintained these elevated antibody levels.
- Antibody efficacy:
- The mRNA vaccine induced greater antibody activity against equine rotavirus A than the traditional vaccine.
- Neutralizing antibodies produced after mRNA vaccination were effective against both G3 and G14 (Group A) rotavirus strains.
- Practical advantages:
- Horses only need two injections of the mRNA vaccine, as opposed to three injections of existing vaccines.
Limitations and Future Directions
The researchers followed the mares and foals for a short period of time (49 days), though they didn’t measure antibody presence in mares’ milk, which could provide antibodies against the virus in the foals’ gastrointestinal tract. “Additionally, all mares except the controls had been previously vaccinated with the standard vaccine, meaning none were naive to the antigen,” said Cohen.
Despite these limitations, he said the results strongly suggest the mRNA vaccines are more effective at inducing long-lasting, viral-neutralizing antibodies in foals and, therefore, are likely to provide better protection than the current vaccines.
Take-Home Message
Cohen’s findings represent a significant step forward in preventing rotavirus-related diarrhea in foals. “This research highlights the potential of mRNA technology to address the limitations of current vaccines,” he said. “A better vaccine is crucial to reducing the prevalence of rotavirus in foals, and these results offer hope for a more effective solution.”

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