As of June 9, the World Health Organization had listed 136 potential vaccines on its registry of candidates to combat the novel coronavirus—also known as SARS-CoV-2—which causes COVID-19. Ten of those are in clinical trials; the other 126 are in what is known as “pre-clinical trials.” What’s the difference? In clinical trials, possible medical interventions are tested in humans. During the pre-clinical phase, they are tested in animals.
The U.S. Food and Drug Administration (FDA) requires pre-clinical testing in both a rodent and non-rodent species as part of its approval process for medical interventions. These tests evaluate the candidate drug for efficacy, toxicity and other safety concerns.
National Institute of Allergy and Infectious Diseases Director Anthony Fauci, MD, explained one key concern with vaccine candidate safety in a March 26 press briefing:
“Now, the issue of safety … there are diseases in which you vaccinate someone, they get infected with what you’re trying to protect them with, and you actually enhance the infection. You can get a good feel for that in animal models. So that’s going to be interspersed at the same time that we’re testing. We’re going to try and make sure we don’t have enhancement. So, the worst possible thing you do is vaccinate somebody to prevent infection and actually make them worse.”
As important as these safety tests are, they are not the only way animal research advances efforts to end the pandemic. Animal models of SARS-CoV-2 have been central to our understanding of the disease to date, contributing to:
Learning How the Virus Behaves
Through animal research, we can learn how the virus moves through the body, details of the body’s immune response and how different levels of exposure changes these processes. For example, studies in ferrets informed our understanding of the role of aerosolized droplets in transmission. Studies in monkeys have shed light on how infection differs by age group and whether a previously infected individual resists reinfection.
Another way animals help us fight SARS-CoV-2 is in the production of treatments. You may have heard about efforts to treat COVID-19 patients with transfusions of plasma donated by already recovered patients. That plasma, called “convalescent plasma,” contains antibodies that helped the recovered patient fight off the virus, so it should be able to help a recipient recover as well. This treatment is, however, limited to the availability of safe and compatible donor plasma.
Researchers are working to scale up this system by growing special antibodies in genetically modified cows. These antibodies have already shown to be four times more effective than convalescent plasma in early clinical trials, and a single cow can produce enough to treat hundreds of patients each month.
As we all watch the research developments and hope for the breakthrough that will allow us to get back to normal, remember to thank the animals underpinning these discoveries.