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The New Bivalent Covid-19 Booster

It Is Safe, But Will It Work?


By now, many people have received three or four doses of vaccines against the virus that causes Covid-19 and some people have gotten the fifth. The first were either two doses of the original mRNA vaccines (often referred to as the Moderna and Pfizer/BioNTech vaccines) or a single dose of the Janssen vaccine, then two boosters after that. At the end of August, the FDA authorized another booster, this one a bivalent vaccine that has two components, one aimed against the original strain of the virus that causes Covid-19 (SARS-CoV-2) and the other against the two Omicron strains that are currently most prevalent, called BA.4 and BA.5.

As with all Covid-19 vaccines, there was immediate objection from anti-vaccination activists, who questioned the bivalent booster’s safety. Those objections are misplaced: the bivalent vaccine is a very small variation on the original vaccines that have been given to billions of doses around the world and that we know are safe. While it is true that at the time of FDA authorization the new bivalent booster had not yet undergone extensive testing in humans, this is standard procedure for tweaking vaccines to meet the challenges of new mutant strains of a virus, as is the case with flu vaccines. There is no reason to be concerned about the safety of the bivalent vaccine.

But Does It Work?

More interesting, however, are the respected voices questioning whether the bivalent vaccine is needed. Among them is pro-vaccine advocate Dr. Paul Offit, the director of the Vaccine Education Center at Children’s Hospital of Philadelphia, pediatrician at the Perelman School of Medicine of the University of Pennsylvania, and a member of the FDA’s vaccine advisory committee. Offit voted against authorizing the new bivalent booster, but the majority of his colleagues on the FDA advisory committee voted for it. The FDA then decided to authorize the new bivalent booster based in part on two datasets. One is from a study of about 800 participants of a booster directed against the first omicron variant, called the BA.1 variant, which showed that it did increase antibody levels against the virus, including against the new Omicron variants. No safety issues were detected in that study, but because BA.1 was quickly overcome by other variants, the FDA asked Pfizer and Moderna to develop vaccines specifically directed against the BA.4 and BA.5 variants. The other dataset comes from preclinical work with the actual BA.4/5 specific vaccine done in mice that also showed a substantial increase in antibody levels against the mutant strains.

Offit and others, however, worry that there is still insufficient evidence to tell us whether the new bivalent booster will offer any increase in protection above what we already have from previous doses of Covid-19 vaccines. Offit is quoted as saying that these increased antibody levels may “not translate to a clinically significant difference.” He believes the shots people have already received are still working well to protect against serious illness and hospitalization from Covid-19 and that the new bivalent booster just won’t add that much.

Studies and Experience Will Tell If the New Booster Works

Everyone acknowledges that we won’t know if the new bivalent booster is effective for some time. Human studies examining the efficacy of the bivalent booster are now being conducted and data may become available soon. It will take many more months to learn from actual experience whether the bivalent booster reduces infection rates from the BA.4 and BA.5 variants, by which time new mutant strains may already have taken over. The BA.7 strain, for instance, had already been reported to be circulating at the time of this writing in early October. It is very likely given the earlier data with the BA.1 booster and mice studies that the new bivalent booster will indeed boost antibody levels over and above even what people who have had all the boosters so far and/or had Covid-19 infection have. What is unclear is whether that boost in antibody levels is needed to enhance protection against serious illness, which already seems robust from the previous shots, or if it will protect against getting infected in the first place.

The concern that people like Paul Offit and others have about the new bivalent booster is that if it isn’t really needed, then it will confuse people and divert resources that might be spent elsewhere. Only about two-thirds of Americans are considered fully-vaccinated at this point and so far uptake of the newest booster has been slow. What are the implications of urging people to have a booster that may or may not be needed? Will people succumb to “booster fatigue” and start tuning out recommendations for vaccines in general?

FDA, CDC, and many infectious disease and healthcare experts strongly recommend that eligible people get the new bivalent booster at least two months after receiving any previous booster. “The COVID-19 vaccines, including boosters, continue to save countless lives and prevent the most serious outcomes (hospitalization and death) of COVID-19,” said FDA Commissioner Robert M. Califf. “As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants.”

There thus seems to be no risk and potential benefit in getting the bivalent booster. The downside is that it might not work to improve upon the protection already in place from previous doses of Covid-19 vaccines. At worst, that would mean a sore arm and a few other adverse side effects for most people without benefit. For the individual, then, the decision to have the booster seems fairly straightforward: small risk, potential gain. But when thinking about the broader issue of how the new bivalent booster will affect populations of people, there is reason for caution. Uptake of boosters has generally been disappointing despite widespread efforts to encourage people to have them. If the uptake for the bivalent booster is low, will it signal a loss of interest in vaccination? Should we be more careful when introducing new vaccines that we can show definitively their value, as we certainly can with the previous Covid-19 vaccines, or does the need to keep up with the fast-moving pace of new variants justify bringing out new boosters even before they have been thoroughly tested for efficacy?

There are no clear-cut answers to those questions and experts disagree. In many ways SARS-CoV-2 virus presents unique challenges that scientists and public health authorities have not confronted before, and we are learning as we go. It is clear, however, that greater attention must be given to the way the introduction of new boosters—or of any significant new health measure—is perceived by the public. If people don’t think the new bivalent booster is necessary, then the public health agencies that want us to have it have failed in their public messaging. We now understand that improving public communication about vaccines is just as important as improving the technologies used to develop them.



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