New vaccine protects against feline leukemia virus

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Merck Animal Health announced the expansion of the recently USDA-approved NOBIVAC NXT vaccination platform to include a solution against feline leukemia virus (FeLV)—one of the most common feline infectious diseases.¹ NOBIVAC NXT FeLV is a nonadjuvanted, low volume 0.5 mL dose vaccination that uses the immune system’s natural strengths to preserve comfort and safety.^1,2 The vaccine is labeled effective against persistent viremia and is indicated for the vaccination of cats 8 weeks or older. The expectation is for the vaccine to be available at veterinary clinics and hospitals nationwide in fall 2024.¹

“We are proud to extend our RNA-particle technology with a vaccine that protects against one of the most persistent threats to our feline patients,” Ian Tarpey, PhD, vice president, research and development, Merck Animal Health, said in a news release.¹ “Merck Animal Health and our NOBIVAC brand have a rich history in vaccine innovation, and we’re continuing to prove our dedication to ensuring there are safe and effective treatment options for veterinary professionals with the latest development of NORBIVAC NXT FeLV.”

NOBIVAC NXT FeLV becomes the only vaccine against FeLV to be built on Merck Animal Health’s RNA-particle technology platform. The vaccine uses the same technology that was used for the June 2024 launches of NOBIVAC NXT Rabies and NOBIVAC NXT Canine Flu H3N2 in Canada and the US, respectively.¹ The vaccine is intended to be administered in 2 doses, separated by 3 to 4 weeks, according to the label and the recommendation of the American Association of Feline Practitioners (AAFP).^1,2 The product has a proven duration of immunity (DOI) of 2 years, as recommended by the AAFP.^1,2

FeLV is among the most common and important infectious diseases in cats. The virus is considered a retrovirus, meaning it could become incorporated into a cat’s genome and may not be cleared over time. Infected cats can shed infectious viral particles in their saliva, feces, urine, and milk.^1,3 The virus commonly spreads through mutual grooming, fighting behavior, and shared food, water, and litter. Exposure to infected cats poses the greatest risk of infection. Although any cat exposed to the virus is susceptible to a FeLV infection, kittens are at a greater risk than adult cats due to their immature immune systems.³

FeLV infected cats initially show no symptoms, although as the virus persists, they can develop cancer, severe blood disorders, and other infections associated with compromised immune systems. Generally, when a cat is exposed to FeLV, their body can react in a few different ways, resulting in either abortive, regressive, or progressive infections:³

• Abortive infections: 20-30% of cats exposed to FeLV develop abortive infections. In these instances, cats can mount effective immune responses against the virus, destroying it before it gets the chance to incorporate itself into the cat’s genome. The cats will gain antibodies against the virus, and they will never test positive for infection using routine tests or show any clinical signs.³
• Regressive infections: Roughly 30-40% of cats infected with FeLV develop regressive infections as a result of partially effective immune responses. The virus is incorporated into the cat’s genome, but the immune system prevented prolonged viral replication, leaving no viral particles in the cat’s blood after the initial infection. It’s unlikely for these cats to experience clinical signs, and they cannot actively infect other cats. There is a chance for the virus to reactivate if they become immunosuppressed, which could leave them symptomatic and contagious.³
• Progressive infections: The worst prognosis of FeLV infection, 30-40% of cats infected with FeLV develop progressive infections, although studies suggest this number is higher in kittens than adults. Cats with progressive FeLV infections are at risk for developing potential fatal associated diseases. Their bone marrow becomes infected, leading to continual viral replication, and they are contagious to other cats.³

“Nearly 4% of cats in North America alone are affected by this disease, a notable percentage when there have been guidelines for prevention in place for decades, and especially since the virus can lead to life-threatening diseases,” Meg Conlon, DVM, executive director, veterinary professional services, Merck Animal Health, said.¹ “That’s why education and awareness of the importance of vaccinating against this disease is so important.”

Merck Animal Health is a division of Merck & Co., Inc., headquartered in Rahway, New Jersey, and known as MSD outside of the United States and Canada. The company has been at the forefront of medical, vaccination, and innovative health-related research for more than a century.¹ Their newest vaccine development could help protect cats across the country from FeLV infections.

References

1. Merck Animal Health Announces Expansion of NOBIVAC NXT Platform with the First and Only RNA-Particle Technology Vaccine for Feline Leukemia Virus. News release. Merck Animal Health. September 24, 2024. Accessed September 24, 2024. https://www.businesswire.com/news/home/20240924377048/en/Merck-Animal-Health-Announces-Expansion-of-NOBIVAC%C2%AE-NXT-Platform-with-the-First-and-Only-RNA-Particle-Technology-Vaccine-for-Feline-Leukemia-Virus
2. Norbivac NXT FeLV. Merck Animal Health. Accessed September 24, 2024. https://www.merck-animal-health-usa.com/nobivac/nobivac-nxt-felv#overview
3. Feline Leukemia Virus. Cornell University College of Veterinary Medicine. Accessed September 24, 2024. https://www.vet.cornell.edu/departments/cornell-feline-health-center/health-information/feline-health-topics/feline-leukemia-virus