Details from a FOIA request to the USDA have revealed severe adverse events following injection of the Nobivac NXT canine flu H3N2 vaccine, the first self-amplifying RNA (saRNA) vaccine widely used in the US for pets. The aftermarket reports received by The HighWire show the first 1,012 pages of 1,888 total pages of adverse events from September 2024 through July 2025. There were 296 cases involving the Nobivac RNA vaccine as a suspect product: 152 were adverse reactions, and 76 were listed as cases of lack of efficacy, meaning the dogs developed respiratory illness or cough after receiving the vaccine.
The dataset shows that there were four canine deaths and one feline death following vaccine administration, but two of the dog cases had significant confounding factors. The other two cases involve dogs that collapsed shortly after receiving the vaccination. In addition, three dogs were euthanized following the vaccine.
-41 cases involved neurological issues
-30 cases of anaphylaxis or hypersensitivity
-52 cases involved vomiting
-19 cases had an injection-site mass/lump/panniculitis/fibrosis/surgery
-26 cases of diarrhea
-5 cases of collapse/shock-type presentations
-4 cases of bloody diarrhea
A 4-year-old golden retriever collapsed 10 minutes after the vaccination, before going into complete cardiac arrest and dying. Merck added anaphylaxis to the report later. A 7-year-old Yorkshire Terrier collapsed 70 minutes after receiving the vaccine, and life-saving care was attempted, but the dog passed away. Diphenhydramine and dexamethasone sodium phosphate were given to the terrier because of previous unspecified vaccine reactions. In addition to the Nobivac flu shot, the 7.33-pound terrier received the Nobivac Canine 1-DAPPvL4 and Nobivac Intra-Trac3 vaccines.
An 8-year-old Shih Tzu was lethargic and vomiting shortly after receiving the vaccination. She was diagnosed with renal failure six days later and euthanized. The event narrative explains that she had received several vaccinations before, including non-Nobivac flu vaccines, but had never received the Nobivac NXT canine influenza vaccine, which is the first approved saRNA vaccine in the country. Merck evaluated this case and said the vaccine was unlikely to be the cause.
saRNA vaccines have limited long-term safety data, much as mRNA vaccines did before they were rolled out to the general public in response to the COVID-19 pandemic. These vaccines are marketed as “innovative, adjuvant-free, non-live vaccines” by Merck.
The first vaccine of its kind was approved by the USDA in 2024 and received limited coverage, but Nicolas Hulscher, MPH of the McCullough Foundation, criticized the lack of safety testing and the manufacturer’s level of transparency.
“It appears that Merck is attempting to camouflage the fact that this product is self-amplifying,” Hulscher wrote. “The primary product description only indicates that it uses ‘revolutionary RNA particle technology.’ However, the novel platform works by RNA particles targeting dendritic cells, where they self-replicate and result in sustained antigen production.“
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