Monkeys, ferrets offer clues in vaccine race

The global race for a COVID-19 vaccine eyes critical questions about how much to rev up immune systems.

The global race for a COVID-19 vaccine boils down to some critical questions: How much must the shots rev up someone’s immune system to really work? And could revving it the wrong way cause harm?

Even as companies recruit tens of thousands of people for larger vaccine studies this summer, behind the scenes scientists still are testing ferrets, monkeys and other animals in hopes of clues to those basic questions — steps that in a pre-pandemic era would have been finished first.

“We are in essence doing a great experiment,” said Ralph Baric, a coronavirus expert at the University of North Carolina, Chapel Hill, whose lab is testing several vaccine candidates in animals.

The speed-up is necessary to try to stop a virus that has triggered a pandemic, killing more than 360,000 worldwide and shuttering economies. But “there’s no question there is more risk in the current strategy than what has ever been done before,” Baric said.

The animal testing lets scientists see how the body reacts to vaccines in ways studies in people never can, said Kate Broderick, research chief at Inovio Pharmaceuticals.

With animals, “we’re able to perform autopsies and look specifically at their lung tissue and get a really deep dive in looking at how their lungs have reacted,” Broderick said.

She’s awaiting results from mice, ferrets and monkeys that are being exposed to the coronavirus after receiving Inovio’s vaccine. Since no species perfectly mimics human infection, testing a trio broadens the look at safety.

And there’s some good news on the safety front as the first animal data from various research teams starts to trickle out. So far, there are no signs of a worrisome side effect called disease enhancement, which Dr. Anthony Fauci of the U.S. National Institutes of Health calls reassuring.

Enhancement is just what the name implies: Very rarely, a vaccine doesn’t stimulate the immune system in quite the right way, producing antibodies that not only can’t fully block infection but that make any resulting disease worse.

That first happened in the 1960s with failure of a vaccine for respiratory syncytial virus, RSV, an infection dangerous to young children. More recently, it has complicated efforts at vaccines against mosquito-spread dengue fever.

And some attempted vaccines for SARS, a cousin of COVID-19, seemed to cause enhancement in animal tests.

Fast forward to the pandemic. Three reported studies in monkeys tested different COVID-19 vaccine approaches, including shots made by Oxford University and China’s Sinovac. The studies were small, but none of the monkeys showed evidence of immune-enhanced disease when scientists later dripped the coronavirus directly into the animals’ noses or windpipes.