COVID-19 vaccine makers’ requests to authorize another round of booster shots have prompted a debate splitting the pharmaceutical companies and vaccine experts who say a fourth jab is not yet needed.
Pfizer and partner company BioNTech, as well as Moderna, the makers of the two-dose mRNA vaccines, have each requested expanded use authorization from federal regulators to administer another round of booster shots to adults, bringing the total number of shots to four.
“I think our data suggests that [fourth doses] are protecting — they are improving dramatically the protection, the fourth dose compared to the third for omicron after some time, after, let’s say, three to six months,” Pfizer CEO Albert Bourla said recently.
Pfizer and BioNTech jointly submitted an application to expand the vaccine’s emergency use authorization to allow for a second booster shot for adults 65 and older, the age group at greatest risk of experiencing severe illness. Moderna’s application is much broader. The company has asked the Food and Drug Administration to greenlight a second booster for all adults 18 and older.
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It’s a matter of debate, though, whether a fourth dose would be advisable. Vaccine experts say recommending a fourth shot for otherwise healthy people, those who do not have underlying health conditions that could worsen symptoms, is premature. While people with compromised immune systems may be encouraged by their doctors to get the fourth dose, people with fully functioning immune systems who have been fully vaccinated with a booster are very well protected. The FDA and the Centers for Disease Control and Prevention also maintain that a single booster dose of an mRNA vaccine from Moderna or Pfizer-BioNTech is sufficient.
“The issue of a fourth dose is not on the current agenda because two doses and a booster are working very well,” said Dr. William Schaffner, an infectious disease expert at the Vanderbilt University Medical Center, who also sits in on the FDA vaccine panel’s discussions about recommending vaccines.
The recent push from vaccine makers to authorize a fourth dose is built on a growing body of evidence that shows antibody responses afforded by vaccines wane over time. Scientists have touted the benefits of boosting in order to maintain protection against new variants, namely delta and omicron.
The most compelling evidence to support the need for a fourth shot comes from a study conducted in Israel, which found that healthcare workers who received a fourth shot on top of two doses of an mRNA vaccine plus a booster at the height of the omicron outbreak were 43% less likely to develop symptoms than those who had not.
Still, the Israeli study results were not a ringing endorsement for extra doses, according to Dr. Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health.
“Some data from Israel on the fourth shot of mRNA had sort of mixed results. There may have been some protection in the elderly population — and that’s really important because that population is more prone to have the severe disease from COVID — but it didn’t do much in the younger populations,” he said.
The boosters currently under debate are engineered to protect against the original “wild type” strain that came out of Wuhan in 2019. Though the mRNA vaccines in use are highly effective against severe illness, continuously boosting with the same formulation targeting the same strain may prompt a substandard immune response.
“This has a lot of experts concerned that perhaps if we keep boosting with the original design to the spike protein over and over again, the more this virus drifts and changes, we may be less likely to recognize it or not respond as well to new versions,” said Tulane University vaccine expert Dr. Lisa Morici.
“What we’re seeing in the short term is that the original design is protecting us extremely well against delta and omicron,” she added.
Scientists are currently searching for a more long-term solution to waning immunity, such as vaccines that address all strains of the coronavirus in one course of shots and can maintain their durability against infection.
Boosting too often with the same or a similar formulation also may not be necessary thanks to the long-lasting immunity afforded by “memory” B-cells and T-cells, which wane very slowly. Those memory cells can stand guard against serious infection for a sustained amount of time.
“One of the things that we have to really start thinking about is pivoting from vaccination strategies that boost your antibody levels for short periods of time and [getting] into investigating strategies that will allow for a more steady but a longer amount of these antibodies to stay in your system because I really don’t want coronavirus vaccinations to become an annual thing,” Pekosz said.
The FDA’s panel of vaccine experts has not set a date to consider publicly whether to expand authorization of the Moderna and Pfizer-BioNTech vaccines. For now, Schaffner said, the pharmaceutical companies should leave vaccine experts at the FDA and the CDC to do their work without pushing for another shot.
“I have no doubt that what they want to do is actually communicate their best scientific judgment, but it’s not good for them to go out and talk about their thoughts on the need for a booster when the official CDC advisory committee’s recommendation is that actually the boosters are doing a good job and we don’t need another just yet,” he said.
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The vaccines currently available have been proven effective at preventing severe disease requiring hospitalization or death — though less so against infection.
“As it happens, these vaccines actually provide pretty darn good protection against hospitalization against the original strain, against delta, against omicron, and even against this subvariant, BA.2,” Schaffner said.
An annual COVID-19 booster would have practical implications as well. People who have yet to receive their first round of booster shots, more than 50% of those eligible, are not likely to sign on for another.
