Coronavirus vaccines should provide protection against COVID-19 for at least nine months, but booster shots might become necessary after that, especially among the elderly, a top Food and Drug Administration scientist said.
The projection comes as scientists and public health officials debate what strategy to pursue on booster shots — whether vaccine manufacturers should produce booster shots that are essentially the same as the original coronavirus vaccines or modify them to target a specific, mutant variant.
Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the FDA, told physicians on Tuesday that the agency will closely watch for waning immunity among vaccinated people with weaker immune systems nine to 12 months after they first received their doses.
“We’re believing that it’s probably going to last at least nine months, but we’re going to be checking this,” Marks said in a call hosted by the American Medical Association. “We need to be careful that in more immunocompromised individuals, particularly older individuals — the oldest individuals who are vaccinated — that we don’t see that drop off more quickly.”
“It is possible — we don’t know for sure — that somewhere at nine months, a year, we may need to have boosters,” Marks said. “But we’ll get a better sense of that, probably with each month, we’ll get more certainty about when that might be necessary.”
Elderly individuals were among the first with access to COVID-19 vaccines in the United States after the FDA granted two vaccines, produced by Pfizer-BioNTech and Moderna, emergency use authority in December.
In recent weeks, the FDA has issued guidelines for vaccine manufacturers on how to submit applications for the approval of vaccine booster shots.
But neither private companies nor the federal government have settled on a strategy on whether to modify the vaccines to target new, emerging variants, which may be able to evade vaccine immunity, or simply to provide booster shots using the original vaccine, which have thus far proven effective enough against the various mutant strains.
One White House official told McClatchy that the Biden administration has remained intentionally vague on its plans for the country’s excess supply of vaccines because they don’t know what works best for boosters yet.
The federal government has purchased roughly double the number of doses that will be necessary to vaccinate every American.
“It may just be by boosting with the same vaccine, you’ll get high enough titers that they would take care of these variants,” said Marks, referring to the concentration of antibodies in the blood provided by the vaccines. “There is something to be said for trying to keep it simple, because the more different types of vaccines that one has to manufacture, you basically take away from some of the capacity to manufacture as much vaccine.”
DETERMINING VACCINE DURABILITY
Dr. Kayvon Modjarrad, director of the Emerging Infectious Diseases Branch at the Walter Reed Army Institute of Research, told McClatchy in a recent interview that scientists are not at the point where they are able to predict when immunity — whether naturally acquired after infection, or through a vaccine — fades.
“When we look at animal studies, we look at antibody levels as one indicator,” Modjarrad said. “They always decline with time. The question is how quickly do they decline and when do they get to a point that is below a threshold of antibody levels that you need to protect against disease. We haven’t quite defined that threshold yet.”
Scientists only know with confidence that a vaccine works for six months, for example, if they have six months of data proving it, Modjarrad said.
Pfizer and Moderna, which both use the same biological technology in their vaccines and were first to complete their clinical trials, have recently published findings that show their vaccines remain over 90% effective after at least six months of data collection.
“All of this is good news, and we’ll find out — we’re looking at the unknown,” said Dr. Larry Corey, who has co-led the coronavirus vaccine clinical trials for the COVID-19 Prevention Network under the National Institutes of Health. “The trials continue. They’ve been designed for two years. And the importance of those continued follow-ups is right in front of us.”
While only six months of data has been collected so far on the advanced, Phase III clinical trial participants, Corey noted that some volunteers who took part in the earliest phases of the trial in the spring of 2020 are now participating in early trials on booster shots.
“They continue to be part of the exploration of what’s needed — do we need to boost, when do we need to boost, and do we actually need to change the vaccine?” Corey said. “Maybe we don’t need to boost everybody, or if we do, we could just give another dose of the same vaccine.”
The Pfizer and Moderna vaccines, which use messenger RNA technology, already appear to differ in effectiveness against new coronavirus variants from the other vaccines — such as those made using viral vector technology, from Johnson & Johnson and AstraZeneca, and other protein-based vaccines.
“Each one is different. We already have data that they’re different, that it’s not going to be one size fits all,” Corey said, on how the government is strategizing for boosters. “The answer to me is different for each platform.”
FDA officials say they recognize there is a need for speed in determining a strategy for booster shots, so that the federal government is prepared for the moment scientists do identify a decline in the effectiveness of the vaccines.
Marks said that for FDA authorization of booster shots, trials will likely involve hundreds of participants, not the thousands who were enrolled in the monthslong clinical trials for the original vaccines.
One FDA official told McClatchy that the agency cannot address specific clinical trials. But it expects the manufacturing process to remain roughly the same, so that companies can essentially pivot from one product to another using the same elaborate infrastructure set up for the original vaccines.
“We want the American public to know that the FDA is using every tool in our toolbox to fight this pandemic, including pivoting as the virus adapts,” the official said.
As public health officials and vaccine manufacturers debate whether to prepare boosters with the original vaccines, or with modified vaccines, some worry that events may force their hands.
Dr. William Schaffner, an infectious diseases expert at Vanderbilt University Medical Center who previously worked at the Centers for Disease Control and Prevention, said coronavirus vaccines may have to be more targeted geographically than flu vaccines.
“The thing with influenza is, if you have dominant strains, they are pretty dominant over huge geographic areas. There isn’t any doubt,” Schaffner said. “At the moment, with COVID, it could become really very localized. They could have variants and strains that are dominant in Europe that are quite different than ours. That could happen in the southern hemisphere also.”
“There are further blank pages in our textbook on COVID, and we’re still writing those as we go along,” he added.