Why don’t we have an Anti-Covid vaccine for pets?

Over the past 12 months, coronavirus vaccines have been applied to billions of human arms — and the furry limbs of many zoo animals. Jaguars have been receiving the vaccine. Bonobos (pygmy chimpanzees), too. The same applies to orangutans, otters, ferrets, fruit bats and, of course, lions, tigers and bears.

But two animals much closer to us have been left out: domestic dogs and cats.

Pet owners are aware of the omission.

“A lot of people ask me about it,” said veterinarian Elizabeth Lennon of the University of Pennsylvania. “When will there be a vaccine for pets?”

A pet vaccine is technically feasible. In fact, several teams of researchers say they have already developed promising vaccines for dogs or cats. The vaccines that have been given to zoo animals were originally created for dogs.

But, according to experts, vaccinating pets is not a priority. While dogs and cats can actually contract the virus, a growing body of evidence suggests that pet dogs and cats contribute little or nothing to its spread and rarely become sick with Covid themselves.

“I think it’s very unlikely that a vaccine will be developed for dogs and cats,” commented University of Illinois Urbana-Champaign veterinarian Will Sander. “The risk of pets getting sick from Covid and the disease spreading among them is so small that a vaccine wouldn’t be worth it.”

Lulu-da-Pomerania tested positive

A woman in Hong Kong was diagnosed with Covid-19 in February 2020. Shortly thereafter, two other people in her household tested positive for the virus, as well as an unexpected family member: an elderly Pomeranian lulu. The 17-year-old dog was the first pet known to have contracted the virus.

But it wasn’t the last. Shortly thereafter a German Shepherd in Hong Kong tested positive, in addition to cats in the same city, Belgium and New York. The cases were very mild — the animals showed little or no symptoms — and experts concluded that it was humans who transmitted the virus to pets, not vice versa.

“There have so far been no documented cases of transmission from dogs or cats to humans,” Lennon said.

But the prospect of a pandemic among pets sparked interest in a vaccine for animals. New Jersey-based veterinary pharmaceutical company Zoetis began work on the vaccine as soon as it learned of the Pomeranian lulu who contracted Covid in Hong Kong.

“We thought, ‘wow, this could get serious. Let’s start working on a product,'” said Mahesh Kumar, vice president and head of vaccine development at Zoetis.

In the fall of 2020 Zoetis announced that it had identified four promising vaccine candidates, all of which elicited “robust” antibody responses in cats and dogs. (The studies are small and unpublished.)

But as vaccine development progressed, it became increasingly clear that the contamination of pets is unlikely to pose a serious risk to animals or people.

In a study conducted with 76 pets that lived with people who had the virus, 17.6% of cats and 1.7% of dogs also tested positive. (Studies have found that cats are more susceptible to infection than dogs, perhaps for both biological and behavioral reasons.) Among infected pets, 82.4% had no symptoms.

“It doesn’t seem likely that dogs or cats will become a reservoir for this virus in the future,” said veterinarian Jeanette O’Quinn of Ohio State University. “We think that if there were no sick people living with them, these pets would not be able to continue to spread the virus from one animal to another. The virus would not continue to exist in this population.”

These factors combined have convinced experts that a pet vaccine is not necessary. In November 2020 the US Department of Agriculture (USDA), which regulates veterinary drugs, said it was not accepting applications for registration of vaccines for dogs or cats, “because the data does not indicate that such a vaccine would be of value.”

taking good care of minks

As the risk to pets diminished, another problem began to draw attention: the coronavirus in mink. These elegant mammals that are bred in large numbers have turned out to be highly susceptible to the virus. Not only were they dying from it, they were transmitting it between them and relaying it to humans.

“I think the mink situation totally justifies the search for a vaccine,” Lennon said.

The USDA shared that view, and in the same statement last November in which it said it was not considering creating vaccines for dogs or cats, the agency said it was open to applications for registration of mink vaccines.

Zoetis changed its focus and decided to adapt one of its dog vaccines to be used in mink. Several other teams are also developing mink vaccines; Russia has already approved a vaccine for all carnivores, including mink, and is said to have already started to apply it to animals.

Mink studies are ongoing, but when news of Zoetis’ work came out, the company began to be sought out by zoos. Some of its animals – including gorillas, tigers and snow leopards – had already contracted the virus. Zoos wanted to try mink vaccine.

“We received a huge number of orders,” said Kumar.

Zoetis decided to supply the vaccine to zoos on an experimental basis and has already committed to donating 26,000 doses — enough to vaccinate 13,000 animals — to zoos and animal refuges in 14 countries.

As a result, many large cats that live in zoos, such as lions and tigers, are being vaccinated, while their domestic cousins ​​are not. This is in part because these species appear to be more susceptible to the virus; some animals have died after being infected, although in many cases it is difficult to conclusively determine what caused the death.

“The big cats seem to be getting sicker than the house cats,” Lennon said.

vaccine for cats

While the evidence available so far indicates that the virus does not pose a serious threat to pets, scientists recognize that there is still much that is not known. It is still unclear how often infected humans transmit the virus to their pets, especially as authorities do not recommend routine testing for pets, and the virus can have health effects on pets that have not yet been identified.

In an article published this month, scientists raised the possibility that the alpha variant, first identified in the UK, could cause cardiac inflation in dogs and cats. The evidence is circumstantial, but the virus has been linked to the same problem in humans, and experts say the connection is worth researching.

“We need to do more research in this area to see if there is a real connection,” said O’Quinn.

There may be individual pets that are at an especially high risk of contracting the virus. Lennon and his colleagues recently identified an immunocompromised dog that appears to have become seriously ill with the coronavirus. Unlike most infected dogs, this animal shed high levels of virus for more than a week.

“Of course it was just one case, but this case illustrates that Covid is not the same for all pets, just as it is not the same for all people,” Lennon said.

It is possible that future research or modifications to the virus will lead scientists to change their minds about a pet vaccine. If the virus turns out to be more prevalent, virulent or transmissible in dogs or cats than is known today, the arguments in favor of a vaccine would be strengthened, scientists said. The USDA said it may revise its position if more evidence of transmission and clinical disease emerges in a particular species.

If that time comes, Kumar said, Zoetis will be prepared to resume its work with pet vaccines. If the company’s mink vaccine is approved, veterinarians can use it in the event of an unexpected Covid outbreak in dogs or cats, even if it has not been licensed for those animals.

New York-based biotechnology firm Applied DNA Sciences has also developed a promising vaccine for cats “just in case,” said CEO James Hayward. Like Zoetis, the company, which works in partnership with Italian Evvivax, is focusing more on a mink vaccine.

_{Translation by Clara Allain}