NPJ Vaccines: Novel recombinant H5-based Vaccine Provides Effective Protection against H5N1 Influenza Virus in Cats

 

Cats As Potential Vectors/Mixing Vessels for Novel Flu

#19,017

Although we've seen HPAI H5 make some abrupt, and unexpected, U-turns in the past (former hotspots Indonesia & Egypt haven't reported a human case in nearly a decade), its recent behavior suggests it is - at least, for now - firmly entrenched in the North American, Asia, South American, and European environment. 

It continues to aggressively spill over into mammals, including livestock, and barring some unpredictable evolutionary twist, seems likely to maintain its endemicity.

As such, it is important we start taking the long view on how we will deal with its continued presence in the years ahead. 

Which is why - despite some logistical challenges and safety concerns - vaccination of poultry and cattle are now being seriously considered both here in the United States and in parts of Europe for the first time.  

HPAI H5's current affinity for felines is another concern, as cats could serve as both a `mixing vessel', and a potential vector of the virus to humans (see JAVMA: Companion Animals and H5N1 Highly Pathogenic Avian Influenza: Cause for Concern?).

Vaccination is an obvious intervention, but - as with poultry, livestock, and even humans - developing a safe, effective, durable, and broadly protective vaccine is a tall order. 

Today we've got a study by researchers from Cornell University, VST LLC dba Medgene, and South Dakota State University on the effectiveness of a novel recombinant H5 vaccine in protecting cats from an H5N1 (genotype B3.13) challenge. 

While the study was small (8 vaccinated, 8 unvaccinated cats), and the end point was 2 weeks post 2nd vaccination (meaning duration of infection wasn't explored), 7 of the 8 vaccinated cats appeared to be fully protected against clinical disease. 

One vaccinated feline briefly shed detectable virus on day 3 post challenge, but all survived. Of the 8 unvaccinated cats, just one survived (the others either died or reached humane euthanization criteria).  

While only the B3.13 genotype was used as a challenge, researchers also showed serological evidence of D1.1 protection based on antibody cross-neutralization in vitro. 

First the link, abstract, and a small excerpt from the study. Follow the link to read it in its entirety.   I'll have a bit more after the break. 

Published: 12 January 2026
Novel recombinant H5-based vaccine provides effective protection against H5N1 influenza virus in cats

Salman L. Butt, Pablo Sebastian Britto de Oliveira, Ruchi Rani, Mohammed Nooruzzaman, Annika N. Diaz, Sherry Glover, Alan J. Young, Bishwas Sharma &
Diego G. Diel 
npj Vaccines , Article number: (2026) Cite this article

We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.

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Abstract

The emergence and broad circulation of highly pathogenic avian influenza (HPAI) H5N1 virus in wild birds and its spillover into dairy cows with sustained transmission in this species pose a major risk to felines, which are highly susceptible and often succumb to the infection.

Here, we developed a novel recombinant hemagglutinin H5-based vaccine and evaluated its safety, immunogenicity, and protective efficacy against HPAI H5N1 virus in domestic cats. Immunization of cats with H5-vaccine candidate elicited robust levels of neutralizing antibodies against H5N1 virus and protection against disease, mortality, and infection upon H5N1 virus challenge. The vaccine-elicited immunity significantly reduced virus shedding and viremia, limiting systemic spread and disease severity in immunized animals.

Importantly, beyond protecting susceptible felids, vaccinating cats against the H5N1 virus could also reduce the risk of human exposure - underscoring the One Health impact of implementing such a vaccination strategy in feline populations.

       (SNIP)

It is important to note that in spite of the robust neutralizing antibody responses elicited by the H5-vaccine in cats in our study, cellular immune responses were not investigated, and thus, the contribution of T cells to the observed post-challenge protection is unknown.

Another limitation is the fact that paired tissues from the H5-vaccinated and sham-immunized animals were not collected during the study. Therefore, direct assessment of the H5 -vaccine on limiting the virus tropism and distribution, tissue replication and damage were not determined.

Another aspect of the H5-vaccine developed here that needs further investigation is the duration of the immunity40 . This would be important to determine appropriate intervals for revaccination of felids in the field. 

In summary, we demonstrate the safety and protective efficacy of a recombinant H5-vaccine against HPAI H5N1 virus genotype B3.13 in domestic cats . In addition to decreasing disease severity and mortality in immunized cats, the H5-vaccine developed here dramatically reduced infectious virus shedding, suggesting that it would be an efficient tool to combat H5N1 virus transmission and spread in felines35 .

        (Continue . . .)

As the excerpt above indicates, there are other limitations to this study, but what they were able to demonstrate is encouraging. While more research is needed, it suggests feline H5N1 vaccination could become an important risk-reduction tool.  

Particularly for zoos with big cats, cats on or near infected dairy farms, feral colonies, and shelter or rescue animals.

For more on the threat posed by HPAI H5Hx to cats, you may wish to revisit:

L.A. County Public Animal Health Alert: Another H5N1 Domestic Cat Cluster Linked To Raw Cat Food

One Health: Outbreak of HPAI a(H5N1) Among House Cats: A Case Series Involving Oseltamivir Treatment

Viruses: The Seroprevalence of Influenza A Virus Infections in Polish Cats During a Feline H5N1 Influenza Outbreak in 2023