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We don’t need universal booster shots. We need to reach the unvaccinated.

The case for boosters for healthy younger adults is not strong — and those shots would do more good elsewhere

A health-care worker administers a third dose of the Pfizer-BioNTech coronavirus vaccine at a senior living facility in Worcester, Pa., on Aug. 25. (Hannah Beier/Bloomberg News)
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Many people are cheering the decision by the Food and Drug Administration last month to authorize coronavirus vaccine boosters for all adults 18 and over — a move that built on an earlier authorization for people over 65, those with underlying health issues and front-line workers. Commentators are hailing boosters as a key tool for getting the pandemic under control, and many public health experts are urging all American adults to get them. In response to incomplete data about the omicron variant, authorities are redoubling their booster recommendations, and the Centers for Disease Control and Prevention this past week advised additional doses for everyone 18 and older.

We don’t think boosters for all are necessary, even with the emergence of the omicron variant. Two of us — Krause and Gruber — were co-authors of a recent article in the Lancet, a medical journal, that summarized all available studies and concluded that the data did not support widespread boosting; the other — Offit — is a member of the FDA vaccine advisory committee that did not support widespread boosting at either of its most recent meetings on this topic, in September and October. While boosting can further increase already very high levels of protection against even mild illness, the only people who really need an additional dose of vaccine are those who are at high risk of serious disease (including the elderly) or who might expose vulnerable household or workplace contacts if they got infected.

Given that protection against serious illness is still strong from the original two doses of the mRNA vaccines, the data simply does not show that every healthy adult should get a booster. Indeed, the push for boosters for everyone could actually prolong the pandemic: The campaign includes exaggerated accounts of the waning efficacy of the vaccines, giving the public — including the vaccine-hesitant — reason to think that the shots are less effective than originally advertised. And promoting and distributing booster shots distracts officials and health-care providers from the far more important task of reaching vaccine holdouts and vaccinating children. It’s striking, for instance, that the new nine-step White House plan responding to the omicron variant emphasizes “boosters for all adults” — it’s in the No. 1 position — but includes no explicit step to improve immunization rates among unvaccinated American adults.

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The fact is that existing vaccines are extraordinarily effective, even over time. During the last few months, studies in New York and North Carolina, which together included more than 17 million adults, found that recipients of mRNA vaccines — specifically Moderna and Pfizer-BioNTech — maintained protection of about 90 percent against moderate to severe disease or hospitalization even six to eight months after vaccination. This is consistent with other data showing that the vaccines induce strong memory immune responses that contribute to long-term protection. Effectiveness against any symptomatic disease (that is, mostly mild) after two doses in both studies remained around 70 percent for the Pfizer vaccine and 80 percent for the Moderna vaccine. (After five months, the effectiveness of the single-dose Johnson and Johnson vaccine was lower than that of the mRNA vaccines but, at about 65 percent, was still similar to the results reported in the original effectiveness studies.)

Some of the drop in effectiveness against mild disease was most likely attributable to the rise of the delta variant, which is now prevalent throughout the United States: To some degree, it wasn’t that the vaccine became inherently less effective; rather, the virus it was fighting changed. That suggests that vaccine efficacy against mild disease may not wane as much in the future (although this could change again, if omicron or another variant becomes more prevalent and better able than delta to evade immune responses against the original virus).

One argument in favor of booster dosing has been the Israeli experience. A frequently cited study out of Israel suggested greater declines in Pfizer vaccine effectiveness over time, but the smaller unvaccinated group in this study increased the likelihood that factors other than vaccination influenced interpretation of the results. For example, if people who were unvaccinated were infected (and thus became more protected against reinfection) over the course of the study, this would make the vaccine effectiveness appear lower over time by comparison. Also, predictions of dramatic loss of vaccine effectiveness in the United States based on early results from this study have not come to pass.

Other data from Israel suggesting that the pandemic came under control as boosting was implemented is likely to have been a coincidence. Similar reductions were seen without boosting late this summer and early this fall in the United States and many other countries, including Bangladesh. These shifts in the epidemic curve were not associated with substantial increases in vaccination rates and were more likely due to other factors, including behavioral changes, protection induced by natural infection and the cyclical nature of the pandemic.

Our views aren’t changed by the data available so far about the omicron variant. We do not yet know how far omicron will spread or if it will be as dangerous as previous variants. Considerably more information is expected soon, so there is no reason to urgently change boosting policy without considering all of the relevant scientific data.

Although we believe it is likely that the current vaccines will continue to protect against severe disease caused by omicron, the possible need for a booster shot targeting a vaccine-resistant variant could be a reason to hold off for now on a booster targeting the earliest version of the virus. For one thing, if omicron proves resistant to vaccine-induced protection against serious disease, then a booster dose with the current vaccine may not help. It’s also possible that repeatedly “training” the immune system to fight the original virus could reduce the effectiveness of a variant-specific booster. This phenomenon, called “original antigenic sin,” has been observed with influenza and human papillomavirus vaccines. In other words, for those not in immediate need of a boost, there may be a significant advantage to waiting until a booster more closely aligned with circulating variants becomes available; boosting on the original antigen could be counterproductive.

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The effectiveness of the current vaccine regimens — using selective, not universal, boosting — is sufficient to meet the two key public health goals: keeping people out of the hospital and reducing transmission to the point where the virus is controllable. It is sufficient, that is, if enough people get vaccinated. In the United States, as elsewhere, unvaccinated people (about 30 percent of the population currently), including children, are the source of most of the viral spread. Unvaccinated adults also suffer the most severe disease and death. The delta variant has heightened their vulnerability: Its increased transmissibility means higher rates of vaccination than originally expected will be required to reach herd immunity. As much energy and as many resources as we can muster — and there are finite amounts of both — should be directed at reaching this population, especially children; reducing minor illness in healthy people won’t get us to herd immunity.

And since the boosters have potential side effects, however rare, it’s important to direct them to the people who will gain a clear benefit. A healthy young person with two mRNA vaccine doses is extremely unlikely to be hospitalized with covid, so the case for risking any side effects — such as myocarditis — diminishes substantially. Also, attempts to maintain protection of 90 percent or more against even mild disease among healthy people could lead to continual boosting and re-boosting, since the immune responses that provide protection against mild disease aren’t as long-lived as those that protect against severe disease. It is unrealistic to expect a vaccine to remain 90 percent effective against even mild illness for an extended period.

Our views are not as far from the official position as they may seem. For mRNA vaccines, based on advice from the Advisory Committee on Immunization Practices, the CDC on Nov. 19 initially issued the fairly tepid recommendation that adults 18 to 49 “may” receive a booster, and those over 50 “should” receive a booster. (It put both groups in the “should” category Monday, without further outside advice.)

The only strategy that will defeat the coronavirus is vaccinating the unvaccinated, wherever they live. The current focus on boosting can interfere with implementing that strategy even in wealthy countries, and it delays vaccination of people in lower-income countries. Those who have not yet been vaccinated remain unvaccinated for different reasons, and it’s wrong to assume that they are all unreachable. The doses contemplated for use as boosters surely would do far more good if they were used to immunize unvaccinated, vulnerable people, whether in the United States or abroad.

It’s not enough to say that it’s logistically impossible to redirect some booster-shot doses now. Decisions about the allocation of doses and resources to help administer them were political choices, not inevitabilities. Even if it is theoretically possible to promote both boosting and vaccinating the unvaccinated at the same time, recent statements by public health officials have focused heavily on boosting.

In September, Rochelle Walensky, director of the CDC, said, “We will not boost our way out of this pandemic.” That remains true. Boosters have a role, but there is no evidence that boosting everyone is the proper course of action.

The views are those of the authors and do not necessarily represent those of the FDA. This article has been updated.

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