Merck’s newer Nobivac NXT Rabies vaccine line for dogs and cats is considered safe and meets standard veterinary regulatory and licensing requirements. However, because it utilizes newer technology, it has generated some online discussion and confusion among pet owners.
A breakdown of what the vaccine is, where online concerns stem from, and what safety data shows includes the following:
What Makes It Different?
The Nobivac NXT Rabies vaccines (such as Nobivac NXT 3-Rabies) are built on an advanced platform. Notably, they are:
Non-adjuvanted: They do not contain adjuvants (substances added to some vaccines to stimulate a stronger immune response). For cats in particular, non-adjuvanted vaccines are often preferred because adjuvants have historically been theoretically linked to injection-site inflammatory issues.
Free of certain additives: They are formulated to be preservative-free, antibiotic-free, and thimerosal-free.
Low-volume: They are administered in a smaller 0.5-mL dose to improve comfort during injection.
Where Do the Safety Concerns Come From?
Because the underlying platform involves newer veterinary vaccine technologies (using RNA particle delivery systems to instruct cells to recognize harmless viral proteins), rumors and misconceptions have circulated online:
Misunderstandings of the technology: Some social media posts have incorrectly conflated these preventative vaccines with unrelated experimental or human medical treatments, or misconstrued how the technology functions.
Misinterpretations of study timelines: Claims have circulated online that the vaccine was only tested for “14 days.” In reality, the 14-day window referred to a specific field-safety observation period within a much broader, multi-year licensing and duration-of-immunity evaluation program.
General Safety Profile
Like any vaccine—human or animal—mild side effects can occasionally occur. These can include:
Temporary lethargy or mild tiredness
Mild discomfort or transient swelling at the injection site
Occasional mild digestive upset (such as minor vomiting or diarrhea)
Serious adverse reactions (like severe allergic reactions/anaphylaxis) are rare, but as with any vaccine, they require prompt veterinary care. Clinical trials and safety studies submitted for licensure have shown it to be well-tolerated in dogs and cats (including kittens and puppies starting at 12 weeks of age).
If you have specific concerns about which rabies vaccine formulation is best suited for your pet’s medical history, age, or lifestyle, your veterinarian is the best resource to guide you.
Questions and Answers from PVC members and the volunteer vets
- Is this vaccine safe for cats? Answer.. We’ve been using the Merck NXT Rabies vaccine in Canada in cats for over 2 years in my multi doctor practice. Haven’t seen a single concern yet. It is definitely tested. Dr.Miller
- My neighbor heard not safe ! Answer… All vaccines released for use in the US have to pass rigorous testing for safety and efficacy. That is after the “research” that the company did in the first place to develop the vaccine. “My neighbor heard about” is not the same thing as scientific research and testing. Dr. Johnson
- Facebook groups say don’t vaccinate! The feedback you will get here is that your concern is due to horrendous dis/misinformation. Yes, at some point every animal that is vaccinated for anything will die. Over the top blaming the vaccine is absurd. That said, there is no vaccine or medication without adverse events. Penicillin has killed a lot of people allergic to it.In the US, rabies vaccination is required by law. Yes, you can choose to not abide by it, and vets are able to refuse service to non-vaccinated pets (excepting emergencies). That said, I work relief and have yet to see it in the 30+ clinics I’ve worked in over the past couple of years. Please keep being responsible and vaccinate your pets for rabies. Dr. B
Confused Online Claims
Some online claims, however, appear to be conflating NXT Rabies with another Merck product, Nobivac NXT Canine Flu H3N2, an RNA-particle vaccine for canine influenza. The USDA’s product records identify these as two toally separate vaccines. And because dog flu is significantly on the decline, that is no longer a common vaccine anyway.y
The USDA also cautions against directly comparing the safety results of different vaccines because differences in study design can make such comparisons misleading. Its summary of studies supporting licensure of Nobivac NXT Rabies explains that limitation.
Looking at the Facts: Where’s the Evidence?
To date, no credible evidence shows that pets have lost their lives due to the Nobivac NXT Rabies vaccine.
The USDA requires vaccine makers to collect and report adverse events to monitor product safety. But assessing safety requires looking closely at each individual case, rather than reacting to alarming claims on social media. While anyone in the U.S. can submit an adverse-event report, it’s crucial to understand a key scientific distinction: just because something happens after a vaccination doesn’t mean the vaccine caused it.
Correlation is not causation. Animals can get sick or pass away after being vaccinated for reasons that have nothing to do with the vaccine itself. To establish a true connection, veterinarians must look at medical history, other treatments, timelines, symptoms, lab work, and occasionally necropsy results.
The most important question isn’t whether a pet passed away after receiving NXT Rabies, but whether serious reactions or deaths are happening more often than they do with traditional rabies vaccines—and whether proof ties those events to the vaccine. Right now, the data simply doesn’t support that.
NXT Rabies is a newer technology, so keeping a close, independent eye on it is still a smart practice. Veterinarians and pet owners deserve open access to safety data, including how many doses have been given, serious incident reports, and expert regulatory reviews.
Please always talk to your veterinarian which vaccines are best for your pet!