Covid vaccine used on apes at San Diego zoo trialled on mink

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At the start of 2021, four orangutans and five bonobos became the first great apes at a US zoo to receive Covid-19 vaccinations. An outbreak in San Diego zoo’s western lowland gorilla troop had caused panic among staff after the virus spread to the animals, probably from an asymptomatic zookeeper. Eight gorillas tested positive – with symptoms such as runny noses, lethargy and coughs – and there were fears the virus could spread to other primates.

“We were approached by San Diego zoo asking if we had any vaccine because the primates were getting sick. Luckily, we had some that we thought would be appropriate,” recalls Dr Mahesh Kumar, a senior vice-president at the US veterinary pharmaceutical company Zoetis, which developed the jab.

The great apes in California have made a full recovery but from the start of the pandemic there have been fears for the wellbeing of our closest cousins. In March 2020, experts warned that it could wipe out populations of chimpanzees, gorillas and orangutans because of their genetic proximity to humans. National parks in the Democratic Republic of the Congo and Rwanda quickly closed their doors to tourists as a precautionary measure, and many rangers now follow strict social-distancing guidelines around the animals. So far, the warnings have not come to fruition, but the virus has spread quickly through other animal groups.

The Zoetis vaccine that the great apes received at San Diego zoo in January and February is being developed especially for mink, after outbreaks in dozens of farms around the world. Sars-CoV-2 is highly transmissible between the animals and has high morbidity and mortality. Another American firm and researchers in Russia are also in the process of developing vaccines for mink, according to the New York Times.

Millions of the carnivorous mammals have been culled as a precaution in Denmark, the world’s largest exporter of mink fur, with corpses buried in shallow graves. Genetic analysis on the Danish strains in the farmed mink found the mutations were unlikely to undermine human vaccines and therapeutics, but several scientists backed the controversial culling to stop the uncontrolled spread through mink populations. Thousands of mink died after catching the virus and it has been detected in wild mink during surveillance of animals near a mink farm in Utah.

If approved for use on mink by US regulators, Kumar believes the vaccine could benefit humans too, potentially stopping the emergence of new coronavirus variants that may undermine immunisation efforts in humans. The company needs to show regulators that the vaccine has a reasonable expectation of efficacy and safety, and is carrying out trials with mink farmers in the US. So far, it does not have blood analysis data on the efficacy of the vaccine in great apes but has found a strong immune response in mink.

“We know clearly that the mink in Denmark were able to pass the virus back to humans. The mink contributed some changes to the virus so we are obviously concerned about the spillover back into the humans from the mink. So by protecting the mink, it prevents the spillover back into the human population,” Kumar says.

“We make and develop vaccines for multiple species, including coronavirus vaccines. So we have been using knowledge to develop this [for Covid-19]. We had several formulations that we’d tested on cats and dogs when we were contacted by San Diego zoo.”

Two white mink look out of a cage

Kumar says Zoetis has received several enquires from other US zoos to use the experimental jab – similar to the Novartis vaccine for humans – after the great ape vaccinations made news around the world. But each jab requires emergency authorisation from the US Department of Agriculture (USDA) and there are strict rules about commercial use of the vaccine, with developers only allowed to sell inoculations for stated species.

Zoetis, which was rolled out of Pfizer in 2013, first started developing the vaccine after family pets in Hong Kong began testing positive for Covid-19, with fears dogs and cats could be vectors for animal to human spread. There is no evidence that is the case, but in the UK vets have warned of a possible link between the Kent coronavirus strain and heart problems in cats and dogs.

In the USDA notice announcing that it would accept licensing applications for mink vaccinations against Sars-CoV-2, the agency said there was very limited evidence that the disease spread between cats and dogs in non-laboratory settings. It concluded that a Covid-19 vaccine for pets would not have value and it would not grant licences for species other than mink without more evidence of transmission. Kumar says Zoetis is ready if the virus changes.

“Obviously, we don’t want it to get into cats and dogs. However, for us, it’s a significant concern that if the virus were to change and mutate so that it becomes more infectious in cats and dogs, we are ready. We are pretty confident that we will have something very quickly if something were to happen like that.”

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