Rabies vaccine hesitancy a recurring topic for NH veterinarians, legislators

Last month, the House Environment and Agriculture Committee recommended reconsidering the contents of a sidelined bill from last session: House Bill 1488, which sought to increase rabies vaccine exemptions for New Hampshire pets. 

The bill was sent for interim study by the full New Hampshire House in March and, with the 2026 session closed and the biennium winding down, was no longer eligible for passage. Instead, the committee voted, 10-1, to recommend the topic be addressed in future legislation.

That move came as a surprise to some.

“Truthfully, we didn’t think it was going to go as far,” said Dr. Jane Barlow Roy, who chairs the legislative committee of the New Hampshire Veterinary Medical Association.

That’s because there is broad consensus among veterinarians that the rabies vaccine — which protects against a disease both transmissible to humans and universally fatal — is safe and life-saving. Yet the bill was driven forward by pet owners concerned about the rare but non-zero occurrence of adverse reactions to the vaccine, reflecting the increasing prevalence of hesitancy around both human and pet shots that is driving the resurgence of some infectious diseases in the U.S.

Committee members said at an October work session they wanted to keep the door open to potential future changes to rabies vaccine guidance and ensure the topic is revisited if more information becomes available. But answering some of the questions raised by pet owners and legislators, veterinarians said, will require research that is complicated and ethically fraught. 

A lethal disease

For household dogs, cats and ferrets, rabies is the only vaccine required by New Hampshire state law.

The viral illness is transmitted when saliva from an infected animal touches broken skin or mucous membranes like those inside the mouth, nose and eyes. The virus moves slowly through nervous tissue, incubating for weeks or more before symptoms like fever, headache, confusion, vomiting, and, later, aggression, difficulty swallowing or paralysis begin to manifest. While post-exposure treatment can prevent the disease from progressing if it is administered soon enough, once symptoms appear, the disease is considered incurable.

Wildlife are the most common transmitters of rabies in the U.S., where the prevalence of vaccines has reduced both the disease’s incidence in domestic animals and the rabies death rate in humans and pets. But globally, about 70,000 people die of rabies each year, and more than 99% of people who get the disease outside the U.S. are infected by a dog, according to the Centers for Disease Control and Prevention.

In the U.S., there was an unusually high number of human exposures documented this year, according to the CDC. And recent research suggests that the disease is responsible for more human deaths nationwide than scientists once believed.

Hesitancy

Kelly Arsenault, a Sandown Realtor, is skeptical about some vaccines. But rabies, she said, is not one that she skips when she brings her small dogs to the vet.

“I believe in the ability of the body to heal,” she said. “However, rabies is not one of them — and I know that — it is not one of those that the body is going to heal from.”

Yet Arsenault, who has for years worked to help rehome and rescue small dogs, also has questions about the rabies vaccine.

More than 150 dogs, most of them fluffy and weighing under 15 pounds, have passed through Arsenault’s care over the years, she said. To date, one that she is aware of has had a significant negative reaction to a vaccine, she said, becoming severely ill after injection. Treating the dog with allergy medication managed the reaction, she said, but it was unsettling. She wonders why it happened and whether the incident could have been prevented.

Negative reactions to vaccines in pets are uncommon, but most often appear similar to what many people experience after a flu shot, like injection site soreness and mild discomfort, said Dr. Lisa Boyer, a Seacoast area veterinarian, in an online seminar this October. Less commonly, severe reactions can involve facial swelling, vomiting or difficulty breathing.

These reactions are managed with veterinary care, said Barlow Roy. And in New Hampshire, as in some other states, a pathway exists in state law to allow owners of pets susceptible to reactions to seek an exemption from the requirement. 

“The process is there for those dogs and cats that truly should not be getting the rabies vaccine,” said Barlow Roy. 

That exemption must be approved by the New Hampshire state veterinarian; after it is granted, exempt animals must be kept away from other animals or muzzled. Owners also assume more liability for their unvaccinated animals.

For these reasons and the lethal nature of the rabies virus, the veterinarians consider the vaccine more than worthwhile for almost all pets.

Yet the online proliferation of information and misinformation about vaccines has raised more curiosity among pet owners, who are asking more questions and starting conversations the veterinarians said they welcomed. However, in some cases, they said, pet owners have also become more likely to push back against professionals’ recommendations.

Titer testing

HB 1488 sought to broaden the allowed cases for rabies vaccine exemptions in New Hampshire under one condition: A pet has received a series of tests attempting to demonstrate that their immune system has responded to the vaccine.

Those tests, known as antibody titers, can measure the level of rabies-specific antibodies, or immune system proteins, in a pet’s blood. The pet’s own white blood cells produce antibodies after they are exposed to the inactivated virus molecules in a vaccine; then the antibodies remain in the pet’s blood, ready to raise the alarm if they ever encounter the rabies virus again, such as if the pet is exposed to rabies from a wild animal.

The idea of a titer testing protocol appeals to Arsenault, she said, because if a test could demonstrate that her pet is protected against rabies, she could skip additional “booster” shots.

But the problem, according to veterinarians, is that there is currently no test that can prove definitively whether or not a pet has enough antibodies to be protected against rabies.

If a titer comes back showing rabies antibodies in a pet’s blood, that confirms that the animal has some degree of immunity against rabies from a previous vaccination, Barlow Roy said. But it takes a certain threshold amount of antibodies to actually combat the virus in the case of a real exposure.

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That makes the rabies titer test unhelpful for two reasons. One limitation, according to American Veterinary Medical Association President Dr. Jennifer Quammen, is that the test is a snapshot in time of a dynamic situation. The amount of antibodies in a pet’s blood changes as time goes on; this is part of the reason booster shots are called for.

Second, scientists don’t have a reliable way of knowing what threshold amount of antibodies a pet’s blood must contain in order for them to be fully protected against the rabies virus. Therefore, in the face of a deadly disease like rabies, veterinarians recommend pets get boosters on schedule to ensure they are protected.

An ethical dilemma

The limitation of the rabies titer test doesn’t apply to some other diseases for which scientists have developed titer testing protocol. Pet owners may opt to use an antibody titer test to guide decisions about booster shots for some other illnesses, like canine distemper and parvovirus, veterinarians said.

With rabies, the factor that has limited the development of a titer testing protocol is the disease’s lethality. 

Reaching a conclusion about what level of blood antibodies is enough to protect a dog requires testing on living animals. Dogs with different levels of antibodies in their blood, for example, would be intentionally exposed to the disease; some are expected to contract the illness. That result helps scientists determine how much antibody is actually protective.

Animals that contract diseases for which treatments exist can be supported after that experiment with medical intervention, Barlow Roy said, making these studies less problematic for investigators. But an animal that begins showing signs of rabies is effectively facing a death sentence, making the protocol more fraught.

“We’re not comparing apples to apples, you know? We’re in the same realm,” she said, describing the differences in rabies titer research versus that on other diseases. “It’s more challenging from an ethical point of view … and that’s why we hesitate,” she said. 

Arsenault said she was conflicted: While she wants the results of the experiment, she also feels moral qualms about what it would necessitate.

“That’s probably where this whole thing gets difficult,” she said. “Would I be willing to be part of that study and watch a dog die from rabies? No … I don’t know if I could live with myself.”

However, some advocates of reducing rabies vaccine frequency have pushed for that research to move ahead, and some studies of limited scope have been completed. That included a 2020 study funded by the Rabies Challenge Fund Charitable Trust that involved the euthanasia of at least 45 beagles, some of which were infected with rabies, raising objections from animal rights groups like People for the Ethical Treatment of Animals. 

But research has not yielded enough data to draw conclusions, veterinarians told legislators at hearings on HB 1488.

Most rabies policy and vaccine guidance is based on a document called the “rabies compendium,” compiled by the National Association of State Public Health Veterinarians. The document is due for revision this year, said Dr. Nathan Harvey, New Hampshire assistant state veterinarian, at an October work session on the bill.

Veterinarians expect that the compendium will include updated guidance on the vaccine, possibly — but not certainly — to include guidance around the use of titer testing. 

“They are looking at whether or not we can start making those correlations to (titer levels) being protective, and that information may come out in the compendium. But we can’t assume that information is going to be published, or not,” Barlow Roy said.

The reality at present continues to be that titer tests cannot replace vaccine programs, for the sake of animal and human health, Quammen said. 

Body size

Some pet owners have also raised concerns about particularly small animals, like the dogs that Arsenault rescues.

Some negative reactions seem to occur with more frequency in small animals, Barlow Roy said, though she stressed that they are still uncommon. 

But while pet owners like Arsenault have asked whether a smaller “dose” of vaccine could be administered to smaller animals, that is misleading, Boyer said. Confusion can arise, she said, because many medications are dosed by body weight. But the way that vaccines work — by triggering an immune response — is not as sensitive to body size, meaning that the amount of a vaccine’s active ingredient that an animal must receive for the vaccine to work is not necessarily different for, say, a Pomeranian and a Lab.

“If you cut the dose in half and assume you have an appropriate dose, you will not be fully vaccinated or fully protected,” she said.

But there are other components besides dead viral molecules in a vaccine, and some formulations exist that deliver the same amount of active ingredient in a smaller volume, Boyer said.

A matter of public health

Veterinarians continue to recommend the rabies booster schedule that is widely accepted as the safest and best option for people and pets.

South Acworth Republican Rep. Judy Aron, who chaired the House Committee on Environment and Agriculture last session but did not seek reelection this fall, said during the Oct. 6 work session that the topic could be revisited by the Legislature if more guidance is released in the revised compendium.

Barlow Roy urged pet owners to discuss any concerns with their veterinarian, including by reporting any incidences of suspected vaccine side effects, which she said clinics routinely share with vaccine manufacturers. 

For Barlow Roy, the urgency of keeping pets protected from the virus is augmented by her compassion for the animals that visit her exam table — and the humans who love them.

“If I ever, God forbid, have an animal in my care that has rabies and it is given to, you know, a child in the household, or another family member, a human, that we could have prevented, that would definitely crush me,” she said. “That’s always the thing in the back of my head: Rabies is 100% fatal. It results in death 100% of the time. I think that’s why we are so adamant about rabies and this whole titer discussion.”