How zoos persuade animals to get the coronavirus vaccine. (M&Ms and ice cream help.)

OAKLAND, CALIFORNIA - JULY 29: Visitors view a grizzly bear in its enclosure at the Oakland Zoo on July 29, 2020 in Oakland, California. The Oakland Zoo reopened to the public after being closed for four months due to the coronavirus COVID-19 pandemic. 2,500 tickets will be available to the public each day and will be issued with staggered entry times. (Photo by Justin Sullivan/Getty Images) (Justin Sullivan via Getty Images)

Just like 189 million Americans, Molly the tiger is fully vaccinated against the coronavirus. This summer, 16-year-old Molly was one of several tigers and more than 50 animals at the Oakland Zoo that received at least one dose of a vaccine made by the New Jersey-based company Zoetis.

Unlike some humans, she didn't hesitate when it came time to get her shot. A keeper gave a verbal command, and she slinked up to the enclosure's fence, offering her hip for the jab. After a few warm-up pokes, a veterinarian injected the vaccine. Then, Molly got a treat: "For all of our large, exotic cats - that's lions, tigers and mountain lions - they're being positively reinforced with goat's milk sprayed in their mouths," Alex Herman, vice president of veterinary services at the Oakland Zoo in California, told me. "They really love it."

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The big cats aren't the only zoo residents who've been trained to receive the vaccines. "The bears got ice cream and whipped cream. To get the chimp to stay still, we gave her marshmallows and M&M's," Herman says.

The Oakland Zoo was one of the first to vaccinate, but others are moving to do the same. The San Diego Zoo, the Denver Zoo, the St. Louis Zoo and the Smithsonian's National Zoo all have started vaccinating some animals, while the Nashville Zoo and Maryland Zoo were, as of press time, waiting on vaccine shipments from Zoetis.

"Is covid-19 a risk to animals? Clearly, yes. Is it safe to vaccinate? Clearly, yes," Herman says. "We are trying to minimize the spread through vaccination. There's so much data that shows that's the path forward for humans and animals." Though the virus's origins remain murky - and the Centers for Disease Control and Prevention says there's no evidence that wildlife is a source of infection for humans - it's clear that all animals, mammals in particular, can get sick from it.

In early 2020, two sniffling dogs in Hong Kong tested positive for the coronavirus. Later, it was discovered that farmed minks were dying of the virus, decimating Europe's mink fur industry and forcing Denmark to cull 17 million minks.

The first animal in the United States to test positive for the coronavirus was a tiger at the Bronx Zoo in April 2020. Months later, gorillas at the San Diego Zoo started coughing - and the zoo called Zoetis to ask about a vaccine for animals. It turned out the company, known for providing pharmaceuticals for livestock and pets, had already begun working on one.

Zoetis, a former Pfizer subsidiary, started by focusing its research on cats and dogs, but the U.S. Department of Agriculture "said that they didn't feel like cats and dogs were going to be a significant concern, so we parked that program," Mahesh Kumar, vice president of global biologics research and development at Zoetis, told me. The company then shifted toward making one for minks, whose pelts are a nearly $50 million industry in the United States. From that program of vaccines, which Zoetis tested on minks, the company was able to provide batches to the San Diego Zoo for its primates.

"Obviously, we are not able to individually license a profile for every species. It's not practical," says Kumar. "So what we decided was to [develop] a vaccine formulation that was safe for all animals." Soon, Zoetis was "inundated" with requests from zoos and, in July, pledged to donate 11,000 doses to nearly 70 zoos across the country. In total, the company has made about 4 million doses so far, most of which have gone to the farmed mink industry.

The animal vaccine has some similarities to the human ones, though they were developed differently. Like the Pfizer vaccine, the Zoetis version is designed to be two shots given three weeks apart. Vials of the vaccine also require refrigeration and need to be used within 24 hours of being opened.

But the Zoetis vaccine doesn't employ messenger RNA like the Pfizer or Moderna human vaccines. Instead, it uses a viral spike protein created in a lab. When injected, it triggers an immune response in the animal's body. It's a technique that Zoetis has used before to create vaccines for animals. In terms of efficacy, Kumar says, it's similar to the human vaccines.

So far, according to zoos, the side effects appear to be minimal, perhaps even less so than with humans. Only one brown bear at the Oakland Zoo, according to Herman, seemed to experience soreness at the injection site after receiving the vaccine.

Zoetis is planning to ship a second round of vaccines in the coming weeks to zoos to immunize mammals that veterinarians and keepers view as most at risk. This list includes primates, big cats, mustelids (such as river otters, wolverines and ferrets), canines (wolves and coyotes), bears (including pandas), flying foxes and hyenas. And this protection is coming not a moment too soon. In September, the National Zoo announced that nine of its lions and tigers had covid. Several got very sick, including the zoo's 16-year-old lioness, Shera, who was showing signs of kidney failure.

The conditions of the felines have since drastically improved, but there is still the possibility of significant lasting impacts, as happens with people. Some "domestic dogs and cats have been shown to have cardiac disease, post-covid infection," the National Zoo's chief veterinarian, Donald Neiffer, told me. "Shera is not out of the woods yet. Whether or not she'll have problems in the future remains to be seen."

It's unclear how the cats caught the virus, with the National Zoo saying it's possible that an asymptomatic person infected the animals. The zoo requires masks in all indoor areas, including for employees. An employee vaccination requirement goes into effect in late November.

Many who work at zoos are concerned that big cats are much more susceptible to covid-19 than other mammals, including their smaller relatives. "The contact you have with a cat at home is much closer, obviously, than a lion at the zoo," says Ellen Bronson, senior director of animal health at the Maryland Zoo. "Even people that are really sick with covid are still cuddling their cats, and [only a few] of them are getting sick. ... But there are cases showing up in zoo cats. It's quite surprising."

While studies are ongoing, it remains a mystery why that is the case. Neiffer believes it comes down to DNA and genetics - that there's something in the larger cats' genes that puts them more at risk. "A cat is not a cat is not a cat. A lot of smaller species of cats are the genus Felis. A lot of the big cats are the genus Panthera," he says. However, it still might be advisable to get your house cat vaccinated eventually, he explains, noting that owners should consider making it part of their "preventive medicine protocols" when a coronavirus vaccine becomes available for pets. (While the USDA continues to assert that there's little need to vaccinate domestic pets, the agency does note that the best way to protect furry friends is for their human counterparts to get their vaccines.)

The Oakland Zoo did get some citizen pushback for its vaccination efforts, from those "not really understand[ing] the science," as Herman puts it. She isn't fazed by the criticism, though, and knows the decision to be an early adopter of vaccination was absolutely the correct one. "Humans are being devastated around the world" by covid, she says. "Animals are being devastated by it as well. It's one health. We have to take good care of the environment, take good care of our human community, and take good care of the wild animals too."

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