Science

How a Zoo Decides Which “High-Risk” Animals Should Get a COVID Vaccine

A Sibirian Tiger hisses in its enclosure.
Morris Mac Matzen/Getty Images

Earlier this month, the Philadelphia Zoo announced that some of its animals would soon receive an experimental COVID-19 vaccine for some of its “high-risk” animals. Several other zoos have already begun to vaccinate their animals, with no sign of any major issues. To understand how a zoo comes to decide which animals are high-risk and how to balance the concerns about a new vaccine with the risk of COVID, Slate spoke with Dr. Keith Hinshaw, the director of animal health at the Philadelphia Zoo. This interview has been condensed and edited for clarity.

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Slate: Can you explain how this came about? 

Keith Hinshaw: We have lots of very endangered primates here at the zoo that are closely related physiologically to human beings and so are susceptible to many of the same viruses and bacteria and parasites. In January of 2021, there was an outbreak of COVID-19 in the gorilla troop at the San Diego Wild Animal Park. To protect the other troop of gorillas that live at the actual San Diego Zoo, they had obtained a small amount of an experimental vaccine from the Zoetis Farm Animal Health company. When we found out that information, we contacted Zoetis directly. Those discussions happened in February. After learning about their vaccine, we asked if we could be put on a list of zoos and other facilities that would be interested in using it on their animals. So we submitted a list to them of the animals that were highest up on our list of priorities.

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Which animals did you decide were at risk?

All of our primates. We also submitted our carnivores, which in our case is bears, animals in the weasel families such as otters, animals in the canid families such as our maned wolf, and then a few other miscellaneous carnivores, such as the red pandas, the meerkats, and a thing called a fossa. We did not submit our list of bats because our bats are behind glass, so there’s not really any air exchange with guests. And we didn’t think that they would be as susceptible to actual illness. So 81 primates and 37 carnivores. In their press release, Zoetis said they’re donating 11,000 doses to zoos and sanctuaries and other institutions, so two doses for each of the animals that I mentioned is 236 doses.

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How did you determine what the at-risk animals were?

There are actual studies where they would see if they could demonstrate that an animal could get infected with the COVID virus. And then there was also a paper published where they did computer modeling to see if the actual shape of the receptor on the lung cells of different species of animals would match up with the shape of the spike protein on the SARS CoV2 virus. It is very theoretical, but it did predict, as you might expect, primates would be susceptible, and cats were up there.

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So you presented all of these animals as equally at risk, as equal priorities? 

For our request to obtain the vaccine, we simply submitted the list, not in any particular order. In reality, once we obtain the vaccine, there is probably a logical order: the great apes—gorillas and orangutans—and then the big cats—lions, tigers, leopards, jaguar—because those are the animals that we know have already been infected at other zoos.

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We’re constantly monitoring both the lay and the scientific press for stories about animals that could potentially be susceptible. And every zoo has to make their own decisions. Some zoos may not use it at all. And some have decided to use it in an even wider-ranging group of animals. If evidence came up that other species appeared to be susceptible, we would certainly add them to that list.

Is this vaccine different from human COVID vaccines?

Yes. This is what I would call a standard vaccine for animals. It does not contain a live virus in it. And it doesn’t contain mRNA. It just contains the antigen, which is a synthesized version of that spike protein from the SARS CoV2 virus, and then a chemical that’s added to make your body’s immune system pay more attention. There’s no virus in there or anything else that might cause any sort of illness. The Zoetis people are recommending two doses three weeks apart, which is pretty standard.

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Would you administer different doses to, say, a gorilla and a lemur?

No, they get the same dose. For most vaccines we use in the zoo, it’s the same dose no matter what size the animal. There are some exceptions—the rabies vaccine, for example—but in general, it’s a set amount. You’re using the vaccine to get the attention of the immune system, and you don’t necessarily need to use a lot.

What have you heard from other zoos that have already begun vaccinating their animals? 

I haven’t heard anything bad. I do know that they’ve done safety trials. And I know they did those trials with dogs and cats and demonstrated that you get an antibody response. The American Association of Zoo Veterinarians has a very active listserv, and there is a lot of interest from the veterinarians to know how things are going with zoos that are starting to implement this vaccine. And when I communicated with Zoetis last week about this, they had not received any reports from anyone of adverse reactions.

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If there were adverse reactions, would you reassess?

Exactly. We will always be paying close attention to whether or not there’s any problems with this vaccine or any other medication in zoo animals. One of the things that makes veterinary medicine interesting is that other than maybe a few parrots—and we’re not totally clear on what is going on there—they can’t tell you what they’re feeling. But I will say that the animal keepers are very observant and will pay very close attention to their animal’s behavior. They’ll know what side of the mouth the animal chews food on, how fast they blink, how fast they stand up and lie down. And so if they see anything that seems different, they’ll give us a call.

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What would it take for you to call off the vaccinations?

Say we gave an animal this vaccine, and for a day, it only ate half as much food as it normally would eat, and then from that point on, it was back to normal again—I would not consider that a serious side effect. If we gave the vaccine and the animal went off food completely and seemed like it was in a lot of discomfort, then we would think more carefully. Or say it developed an abscess at the vaccine site, like a severe kind of localized reaction. That would be a little bit concerning, and we would have to think carefully about using this vaccine in that species. But other zoos are implementing the vaccine and have not reported any severe side effects. So, so far, so good. And then the more tricky ones, I guess, would be longer term side effects; you might not know for a long time if there’s an issue. But given the technology of the vaccine, which is a fairly standard animal vaccine, I don’t anticipate that we will see those effects either.

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Did you have to have a serious conversation about risk before you agreed to do this?

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We did have the conversations. We have a weekly meeting with the zoo veterinarians, the nutritionists, the curators, the director of the zoo, our records people, and so on. We felt it was important to talk about it. Every zoo is going to have to make their own decision. Like if you’re in an area of the country that has low community transmission of COVID, and your keeper force is fully vaccinated, and if you’re in a climate where a lot of the animal housing and activities happen outdoors, you may not see that as necessary.

There was an outbreak of COVID-19 in a group of lions at a zoo in India in May with the delta variant. The outbreak that you heard about in the Bronx Zoo in April 2020 was with the original strain. Those cats went off feed for a little bit; there was some coughing and some nasal discharge, but they didn’t really require any intervention. These lions in India got really sick, and two of them died. So now if you’re a zoo veterinarian, and before you weren’t too worried about this, now maybe the delta variant is a little more of a potential hazard. That could sway your opinion.

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Is your concern just about the animals getting sick?

There’s been little evidence that animals can transmit the virus back to people, at least from domestic dogs and cats and so on. The CDC says that pets are not really considered as a major source of the virus. But there were some issues when this virus got into mink farms in Europe, and they detected the virus was going back into the workers at those farms. We don’t have mink here, and we’re not ever planning on having them, but we do have otters and they’re in the same family as mink. So one of my concerns is that if we did have an infection in our animals, does that put our keepers at any risk? So that would be a second reason. The third reason is that anytime that a virus infects a person or an animal, you can get more variants created, so we want to minimize that.

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How hard will it be to actually administer the vaccines?

We do have a vaccination program already in place. At our zoo, a tiger for example would normally get three vaccines every year. Most of the cats and the great apes—the gorillas and orangutans—are trained for voluntary vaccination, so they will be easy to vaccinate. And then the smaller animals are trained to go into a little mesh box, so those will be fairly easy. The trickier ones are going to be some of the mid-sized primates that maybe aren’t so interested in voluntarily being injected and are also super smart. In our case—other zoos may have better behaved ones—our gibbons are ridiculously smart, and they have not responded as well to the operant conditioning for training voluntary injections. So if I would have to pick [the hardest] one, I would say the gibbons. For those animals, we would probably do the vaccine as part of a regular physical exam under anesthesia.

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So where do things stand now for your plans?

We submitted our list of animals that we were interested in vaccinating in late February. Zoetis needs to get approval from each individual state Department of Agriculture. In our case, it’s the Pennsylvania Department of Agriculture, and there are some forms and paperwork that they need to complete. When I communicated with them a couple of weeks ago, I think they said they were working on 85 different approvals. We’re hoping to receive our first doses some time in the next month or so.

Is there anything else that you wanted people to know?

We would love it if more people would get vaccinated. The virus is actually on the upswing because of the delta variant, and so we’re a little concerned that we could still have our animals exposed one way or the other. So here’s one more person telling you that if you are eligible to get the vaccine, and you haven’t gotten it yet, please do so because it’s going to also protect our animals here at the zoo.

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