Hunt on for a number that brings immunity
Determine the level, then count antibodies
To prove their COVID-19 vaccines worked, companies had to enroll more than 100,000 participants in monthslong clinical trials. Next time, Peter Gilbert wants such tests to require only a few hundred people and eight weeks’ time.
To get there, Gilbert and others have to figure out how much protection people need to avoid hospitalization and death from COVID-19, or even to prevent getting infected at all.
But 15 months after COVID-19 shut down most of the world, it’s still not clear what level of immune protection is enough.
“I haven’t seen people tossing around a number, and I’m a little surprised by that. I would have thought we were further along by now,” said John Grabenstein, editor for the Immunization Action Coalition.
Gilbert and others are hunting for a number that corresponds to immunity against COVID-19. Called a “correlate of protection,” it can indicate whether someone is safe from getting the virus.
Such a figure – measured by a specific type of immune antibodies in a person – could show whether a person had developed enough immunity from a vaccine or natural infection. And it could quickly show if a vaccine was effective enough, without the need for large-scale, lengthy trials.
It’s something scientists the world over would find extremely useful as more vaccines, and possible boosters, are created.
“All you’d have to do is vaccinate people with a new vaccine, measure their antibodies and you’re done,” Gilbert said. “And you could do it with maybe 400 people instead of 40,000.”
Gilbert is a biostatistician at the Fred Hutchinson Cancer Research Center in Seattle who also leads the statistical center for the federal government’s COVID-19 Prevention Network.
As information comes in, the network will evaluate data on the antibody levels of people who’ve either recovered from COVID-19 or been vaccinated against it. Then researchers will look at how many people go on to contract COVID-19 a second time, known as breakthrough infections.
“It’s hard to give a timeline. Maybe June, maybe something else. It doesn’t depend entirely on us; it also depends on when the data sets are final,” Gilbert said.
Getting data takes time because the current vaccines are so good there aren’t many cases breaking through. The Centers for Disease Control and Prevention estimated that out of more than 75 million fully vaccinated Americans, only 5,800 were reinfected.
Once enough of those people have been tested, their levels of antibodies can be compared with levels in people who didn’t get COVID-19 again.
The idea is to set a cutoff: Above that number of antibodies, you’re protected; under it, you might not be.
At least that’s the hope, said Dr. William Moss, executive director of the International Vaccine Access Center at Johns Hopkins University.
“Unfortunately, reality is a bit more messy,” he said. “I think we’ll have some ideas about a range above which most people are protected and then below which most people will be unprotected, but it won’t be a clean cutoff.”