We’ll Probably Need Booster Shots for Covid-19. But When? And Which Ones?


As the nation edges closer to President Biden’s goal of a 70 percent vaccination rate, many people are beginning to wonder how long their protection will last.

For now, scientists are asking a lot of questions about Covid-19 booster shots, but they don’t yet have many answers. The National Institutes of Health recently announced that it has begun a new clinical trial of people fully vaccinated — with any authorized vaccine — to see whether a booster of the Moderna shot will increase their antibodies and prolong protection against getting infected with the virus.

Although many scientists estimate that the Pfizer-BioNTech, Moderna and Johnson & Johnson vaccines authorized in the United States will last at least a year, no one knows for sure. It’s also unclear whether emerging variants of the coronavirus will change our vaccination needs.

“We’re in uncharted waters here in terms of boosters,” said Dr. Edward Belongia, a physician and epidemiologist at the Marshfield Clinic Research Institute in Marshfield, Wis.

Different pathogens affect our immune system in different ways. For some diseases, like the measles, getting sick once leads to lifelong protection from another infection. But for other pathogens, our immune defenses wane over time.

In some important respects, vaccines mimic natural infections — without requiring that we actually get sick. Measles vaccines can produce lifelong immunity. Tetanus vaccines, on the other hand, generate defenses that fade year after year. The Centers for Disease Control and Prevention recommends getting a tetanus booster once a decade.

And sometimes the virus itself can change, creating a need for a booster to produce a new, tailored defense. Influenza viruses are so mutable that they require a new vaccine every year.

The short answer is that we can’t be sure yet, since people started getting vaccinated in large numbers only a few months ago.

“Even in the trials, we don’t know what the immune response is a year out,” said Dr. Kirsten Lyke, a vaccine expert at the University of Maryland School of Medicine and a leader of the N.I.H.’s booster trial.

Just because a variant can dodge existing vaccines doesn’t mean that it will become a widespread problem, however. Beta, for example, has remained rare in countries with strong vaccine programs, such as Israel, Britain and the United States. If Beta stays rare, it won’t pose a serious threat.

But evolution still has a lot of room to play with the coronavirus. Scientists can’t rule out the possibility that new variants may emerge in the months to come that spread quickly and resist vaccines.

“It’s clear that variants are inevitable,” said Dr. Grace Lee, associate chief medical officer for practice innovation and infectious diseases physician at Stanford Children’s Health. “I think the question is, how impactful are they going to be?”

Possibly. In fact, a lot of research on other diseases suggests that switching vaccines can strengthen boosters. “This is a tried and true concept from before Covid,” Dr. Lyke said.

Dr. Lyke and her colleagues are testing this mix-and-match option for boosters as part of their new trial. They are recruiting volunteers who have been fully vaccinated by any of the three vaccines authorized in the United States — Johnson & Johnson, Moderna and Pfizer-BioNTech.

All of the volunteers are receiving a Moderna booster. The researchers will then observe how strong of an immune response it produces.

It’s possible that other vaccines still in clinical trials may work even better as Covid boosters. Novavax and Sanofi, for example, are both running clinical trials in the United States on vaccines that consist of viral proteins. Dr. Lyke and her colleagues have designed their study so that they can add more such vaccines to the mix later on.

“Behind the scenes, we’re working on other contracts so that we can move additional boosters into the trial,” she said. Those additional boosters may also include ones tailored for variants, like the one developed by Pfizer-BioNTech.

Other mixed booster trials are also underway. In Britain, scientists are giving volunteers vaccines from AstraZeneca, CureVac, Johnson & Johnson, Moderna, Novavax, Pfizer-BioNTech and Valneva as boosters. ImmunityBio is testing its vaccine in South Africa as a booster for the Johnson & Johnson vaccine, while Sanofi is preparing to test its vaccine as a booster for those from several other companies.

The N.I.H. trial may start delivering results as soon as the next few weeks. If fading vaccines and surging variants create a burst of new infections this winter, Dr. Lyke wants to have data that she can share with policymakers.

“For us, getting an answer as soon as possible was critically important,” she said. “We just don’t have that luxury of time.”

Dr. Hensley says it’s wise to prepare for the possibility that boosters will be needed. But he hoped that they didn’t become a distraction from the pressing need to get first doses to billions of people across the world.

“If more people get protected right away, then the virus will have fewer hosts to infect and less opportunity to evolve into new variants,” he said.

“I want to see these vaccines distributed globally, because I want to protect people across the world,” Dr. Hensley added. “But even if you only care about yourself, you should get behind this effort as well, because that is the only way that you’re going to end the pandemic and limit the ability of variants to arise.”

Noah Weiland contributed reporting.



Source link Health

Be the first to comment

Leave a Reply

Your email address will not be published.


*