Scientists from San Diego to Boston to Oxford, England, have released results from studies in which monkeys given experimental COVID-19 vaccines were then deliberately infected with the novel coronavirus. And while the specific vaccine formulations differed, all induced immune responses that stalled the growth of the virus.
The recent results encompass vaccines in development by Moderna, Johnson & Johnson, AstraZeneca and local biotech Inovio Pharmaceuticals.
The findings are no guarantee that any of these vaccines will protect people against COVID-19. Monkeys, or, as scientists call them, nonhuman primates, are, well, not human. It will take a clinical trial to know whether a vaccine is safe and prevents disease, such as Moderna’s 30,000-person trial, which launched nationwide Monday.
But the findings are nonetheless encouraging, says Dennis Burton, a vaccine expert at Scripps Research Institute.
“The series of reports are all pointing in the same direction,” Burton said. “That’s good. Inducing the right responses suggests that you’re on the right track.”
WHY DO THESE STUDIES?
Monkeys infected with the novel coronavirus don’t develop the full-blown COVID-19 respiratory symptoms that some people do, but the virus can still replicate in their lungs. That makes monkeys a useful testing ground for whether a vaccine slows viral growth, which researchers believe would make it harder to spread the virus.
“As far as we know, anyone who has the virus can transmit it,” wrote Dr. David Pride, who oversees UC San Diego’s coronavirus testing. “We assume that those who are shedding higher levels of the virus are much more infectious than those who are shedding low levels.”
The setup for these studies is simple: administer a vaccine, then infect with a controlled amount of virus. Researchers can then test an animal’s blood for signs of an immune response and measure the amount of virus in its airways.
Some have even suggested similar studies in young, healthy people. But that raises thorny ethical issues. There are no surefire cures for the novel coronavirus, and health care providers are still learning more about how COVID-19 complications can linger long after the virus is gone. So despite the fact that some young people have volunteered for human challenge studies, these studies are not currently being done for COVID-19.
WHAT DO THE LATEST STUDIES TELL US?
The nitty-gritty of the immune responses triggered by the vaccines differed a bit from study to study, as did the vaccines themselves. But all four vaccines made monkeys produce antibodies, Y-shaped immune proteins that grip the surface of a virus and can prevent infection, and activated T cells, which can kill infected cells. Vaccinated monkeys that researchers then deliberately infected had less virus in their airways than those that didn’t receive a vaccine.
Inovio reported that immune responses in monkeys who were given its vaccine lasted at least four months after the start of the study. Unlike the other research groups, Inovio’s findings are still undergoing peer review by a scientific journal.
“We are very encouraged with the duration of protection,” said Dr. Kate Broderick, Inovio’s senior vice president of research and development. “A vaccine that only provides protection for a very short period of time is not going to realistically solve the problem of this pandemic.”
But only a clinical trial can show how long responses to any of the vaccines truly last, Burton says, which could dictate how often people will need to be vaccinated: “It won’t be that long until you get answers in humans, which is what really matters.”