Cindy Marabito runs a pit bull rescue out of her house in Austin, Texas. "We're the only raw-feeding, holistic, completely no-kill pit bull refuge and rescue in the United States," she says. She currently has nine dogs that roam her big, mulched backyard by the banks of the Colorado River.

The philosophy of her rescue is to give "low to no vaccines."

In most states – including Texas – dog owners are required to give their pets a rabies shot every three years. Health officials say the shots keep rabies – a disease with a 99% fatality rate for humans and animals – at bay.

But Marabito considers the current vaccination guidelines "excessive." She's one of many pet owners with "canine vaccine hesitancy," a phrase coined in a recent study led by the Boston University School of Public Health and published in the journal Vaccine. The study found that 53% of U.S. dog owners surveyed question whether the rabies vaccine is safe, whether it works, or whether it's useful.

The researchers sought to quantify a sentiment they were seeing in their work as veterinarians.

"It's something I deal with on a day-to-day basis," says Gabriella Motta, a veterinarian at an animal hospital in Glenolden, Pa., and a co-author on the paper. "We're [often] dealing with an aggressive animal that's not vaccinated where the staff is taking extra precautions, really making sure not to get bit."

Motta's survey focused on the rabies vaccine, considered by health officials and many veterinarians and health officials to be the most critical dog vaccine for public health – and one that's required by law in almost every state.

That around half of all dog owners are skeptical about the rabies vaccine is "very disturbing" to Lori Teller, a veterinarian at the Texas A&M School of Veterinary Medicine and Biomedical Sciences and past president of the American Veterinary Medical Association. "The rabies vaccine has been around for decades and it is so incredibly safe, especially when you consider the risk of death," she says.

Rabies is nearly always fatal if it advances to the point where symptoms appear.

Understanding the risk and benefits of vaccination

Marabito hikes almost every day with the dogs in an area with "all kinds of wildlife – from raccoons to skunks to possums to deer," she says.

Like most people today, Marabito has never seen a rabid animal, so she says she considers the risk of rabies to be low.

More than 10 years ago, however, she says she saw one of her foster dogs have a bad response to a set of vaccines, including the rabies shot – "reacting violently", she says. That made her wary of the vaccines.

Serious side effects from the rabies vaccine are very, very rare, say Ryan Wallace, a veterinary epidemiologist and lead for the Rabies Team at CDC.

Of the approximately 24 million dogs that are vaccinated against rabies each year, "the vast majority ... have no adverse reactions to the vaccine," he wrote in an email, "There are only a very small number of severe adverse reactions per year (~2.4 per 1,000,000 vaccinated) and, even with those, it's difficult to definitively attribute these reactions to vaccination."

In comparison, Wallace sees great benefit to rabies vaccinations. He analyzed rabies data and estimated that they prevent nearly 300 dogs from getting infected with rabies per year, in turn preventing more than 100 human deaths and saving more than $3 million in treatment costs.

Not vaccinating against rabies could lead to your dog dying if they get infected – or in some cases – if they bite someone, Teller from Texas A&M says: "There is a real likelihood that animal control could euthanize your dog and test it for rabies because human health is going to supersede animal health at that point," she says.

'The most dreaded of all diseases'

A hundred years ago, rabies was arguably "one of the most important of health problems" in the U.S., according to public health researchers at the time.

"The suffering and fear caused by it are so great that they make this the most dreaded of all diseases," wrote the authors of an article from 1928 in the American Journal of Public Health. In the early 1900s, thousands of pets and farm animals caught it each year, and dozens of people died from it.

After decades of concerted public health efforts, the rabies situation in the U.S. was brought under control in the 1960's, and remains so — meaning most human deaths are prevented. Each year, a few hundred pet cases are reported, and one to three people die from it.

Most people in the U.S. aren't vaccinated, and if a person is bitten by a rabid animal, they need immediate emergency prophylactic treatment.

In 2007 the specific variant that typically affects dogs was eliminated in the U.S., but other rabies strains continue to spread among wildlife, so pets remain at risk — and still need to be vaccinated.

CDC surveillance detects around 5,000 rabid animals – mostly wildlife – each year. Bats with rabies are found in every state except Hawaii; other mammals including raccoons, skunks, foxes, wolves and mongoose can also spread rabies in parts of the country.

Pets and people can get exposed through interactions with feral animals. "We have instances every year where a dog has tried to eat a bat," says the CDC's Wallace. There have also been reports of rabid skunks in doghouses and "rabid raccoons and skunks that, for some reason, really like cow pens," leading to rabid cattle, horses and farm dogs.

Globally, rabies is still considered "one of the most feared infectious diseases worldwide," according to health researchers. The disease kills around 59,000 people each year, mostly in countries in Asia and Africa where the disease is endemic in dogs.

From a bite to the brain

The rabies virus is usually transmitted by the bite of an infected animal. Virus in their saliva gets into the muscle. It travels slowly up the nerves, at a rate of about a centimeter a day, to the brain.

There, in the brain, the virus starts replicating rapidly. That's when an animal or a human starts showing signs. "It's almost impossible to come back after that," Wallace says. "The virus's goal is to make you act abnormal so it can spread to the next animal."

It messes with the nervous system, throwing off the body's ability to regulate heart rate and blood pressure, sometimes causing seizures and heart attacks. It can lead to severe swelling in the brain and spinal cord. It migrates to the salivary glands, shedding through saliva and drool. For a patient showing these symptoms, there's no cure at this stage and most die.

The way to prevent this in humans is to not get bitten by a rabid animal; or to get a series of shots soon after, before symptoms appear, to stop the virus from getting to the brain.

The way to prevent this in pets is to vaccinate them before they get exposed.

Canine vaccine hesitancy 'spillover' from humans

"Vaccine skepticism towards pets does not necessarily come from a bad place," says Matthew Motta, assistant professor of health law, policy and management at the Boston University School of Public Health, and a co-author on the Vaccine paper with his sister Gabriella.

"If you're a type of person who believes that vaccines are unsafe, then it is because you love your pet that you wouldn't want to vaccinate them," even though "this position is at odds with the best available scientific research" and evidence, he says.

Motta sees pet vaccine skepticism as a "spillover effect" from a rise in human vaccine hesitancy – related to the skepticism towards COVID vaccines and the anti-vaccine movement against childhood shots. "We see in our research that people who hold negative views toward human vaccinations are precisely the types of people who hold negative views toward vaccinating their pets."

While many dog owners have some skepticism towards the rabies vaccine, the shot is required by law in most places and 84% of the Mottas' survey respondents said they're still giving it to their pets. That's about the same as it was a decade ago, the CDC's Wallace says, according to a separate study conducted then.

Health officials say the margin is slim. The World Health Organization and CDC both recommend maintaining at least a 70% dog vaccination rate, to prevent rabies outbreaks. If the rate dips below that, parts of the U.S. could start seeing more deadly rabies cases in people and pets, Wallace says.