10/21/2026
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This is great information and worth sharing.
While we currently do not stock any vaccines using this technology, we may in the future.
mRNA Vaccines in Pets: Separating Facts from Misinformation
We have been getting some questions about mRNA vaccines, so we wanted to address misinformation and concerns about this type of vaccine in pets. There have been social media posts about Merck's Nobivac NXT vaccines that contain misleading or unsupported claims. New medical technology can be a little scary, but let's clarify some things about these vaccines.
How Do Vaccines Work?
Vaccinations are meant to prepare the body's immune system to recognize viruses or bacteria. The immune system creates antibodies and memory cells that help it recognize a specific germ if the body is exposed again, helping prevent serious illness.
Vaccines use different methods to stimulate an immune response. Some contain a weakened live or inactivated form of a virus or bacterium, while others contain a specific protein or other piece of the germ. Newer vaccine technologies may use messenger RNA (mRNA) to deliver genetic instructions to cells to create a harmless viral protein that the immune system can recognize and respond to.
Vaccines are designed to protect against disease, not cause the illness they are meant to prevent. However, vaccines may cause an inflammatory response as the immune system responds, leading to temporary side effects such as fever, aches, or lethargy. In other words, you may feel ill for a short time after receiving a flu shot, but you do not actually have the flu. As with any medical treatment, adverse reactions are possible, although serious reactions are uncommon.
What Is an mRNA Vaccine?
In simple terms, messenger RNA delivers a code to cells to build a protein. An mRNA vaccine delivers instructions to make a harmless protein from a virus that the immune system can recognize. The synthetic mRNA used in vaccines degrades in the body within a few days. The RNA technology in this type of vaccine cannot enter the cell nucleus where DNA is stored and is not able to alter the genomic DNA of a person or animal.
How Do Nobivac NXT Vaccines Work?
Merck's Nobivac NXT canine influenza and feline leukemia vaccines use a related RNA-particle technology that employs self-amplifying RNA (saRNA). The saRNA makes additional copies of the relevant genetic instructions for a limited time, allowing cells to produce more of the target viral protein and enhancing the immune response. Although the RNA can amplify itself and support protein production for longer than conventional mRNA, it is eventually broken down through normal cellular processes. It does not integrate into the dog's or cat's DNA or persist indefinitely.
These vaccines are designed to use a relatively small amount of saRNA, reducing the amount of genetic material and the volume of liquid that needs to be injected while stimulating an immune response. These saRNA vaccines are also formulated without adjuvants, such as aluminum or chemicals that are added to some vaccines to enhance the immune response.
What About the Social Media Posts?
Some social media posts have made alarming claims about Nobivac NXT vaccines, including suggestions that saRNA spreads throughout the organs and brain or causes drooling, seizures, increased aggression, paralysis, and death.
These claims should be evaluated against the available scientific evidence, product information, and vaccine safety studies. The mechanism of RNA-particle vaccines does not support the claim that the vaccine's genetic instructions permanently alter an animal's DNA.
It is important to distinguish a documented adverse event from a claim that a vaccine caused it. A health problem occurring after vaccination does not, by itself, prove that the vaccine caused the problem. Reports of seizures or other neurologic signs should be evaluated in the context of the animal's medical history, other possible causes, and the available evidence.
Some confusion may stem from research into experimental mRNA vaccines designed to treat gliomas, a type of brain tumor in dogs. Some dogs in that research experienced seizures, but seizures can also occur as a result of the brain tumor itself. Those findings do not establish that the Nobivac NXT vaccines cause seizures. The experimental cancer treatment uses a different approach and should not be confused with the licensed preventive vaccines discussed here.
Are Nobivac NXT Vaccines Safe?
Like all vaccines, Nobivac NXT vaccines can cause adverse reactions. Mild reactions may include temporary lethargy, discomfort at the injection site, vomiting, or diarrhea. Allergic reactions can also occur with any vaccine, and severe reactions require prompt veterinary attention.
The NXT vaccines have undergone rigorous testing and licensing by the USDA’s Center for Veterinary Biologics (CVB) to ensure safety, efficacy, and food/environmental safety before approval. This process evaluates vaccine safety and effectiveness, along with applicable manufacturing and other regulatory requirements. Continued monitoring and reporting of suspected adverse events are also important parts of vaccine safety.
The Nobivac NXT feline leukemia and canine influenza vaccines became available in the United States in 2024. Patton Veterinary Hospital does use the Nobivac NXT canine influenza vaccine. To date, we have not observed serious problems that we have attributed to this vaccine in our patients. Our experience is reassuring, although individual experiences cannot replace larger safety studies.
Does My Pet Need These Vaccines?
The canine influenza and feline leukemia vaccines may be recommended for dogs and cats with lifestyle risks that make them more likely to be exposed to these viruses. Your veterinarian can help determine which vaccines are appropriate based on your pet's age, health, lifestyle, and risk of exposure.
Please do not rely solely on alarming social media posts when making decisions about your pet's health. Instead, discuss any concerns about vaccine technology, safety, or potential side effects with your veterinarian and veterinary healthcare team. You can also consult reputable sources such as the American Veterinary Medical Association (AVMA), the American Animal Hospital Association (AAHA), and the USDA, as well as published vaccine studies, to learn more.
Our goal is to ensure your pets receive the core vaccines that all pet should have, as well as any additional vaccines appropriate to keep them safe and healthy based on their individual lifestyle risks. We want you to feel informed and comfortable discussing these decisions with us so we can partner with you in keeping your pets as safe and healthy as possible.
This blog brought to you by the Patton Veterinary Hospital serving Red Lion, York and the surrounding communities.
This content was drafted with the assistance of an AI language model and reviewed for accuracy by Patton Veterinary Hospital.
Additional Resources
AAHA: RNA Vaccines—The Way of the Future? — An overview of RNA-particle vaccines in veterinary medicine, including safety information for NXT products.
USDA APHIS: Veterinary Biologics Product Summaries — Regulatory summaries of safety and effectiveness studies supporting vaccine licensure.
Merck Animal Health: Nobivac NXT Overview — Manufacturer information about Nobivac NXT technology.
Merck Animal Health: Nobivac NXT Canine Flu H3N2 — Product-specific information about the canine influenza vaccine.
Merck Animal Health: Nobivac NXT FeLV — Product-specific information about the feline leukemia vaccine.
Published Study: Nobivac NXT Rabies Vaccine — A study examining the safety and duration of immunity of the NXT rabies vaccine in dogs and cats.
Published Study: Systemic mRNA Vaccines in Canine Brain Tumors — Research into an experimental mRNA-based treatment for canine gliomas, a different application from preventive NXT vaccines.
