Oct 20, 2021 7:00 AM

More Covid Vaccine Boosters Are Coming. Who Should Get Them?

Federal advisers meet again this week to discuss third shots, but it’s still not clear what the best timing is—or what the US owes the world.

In the next few days, an advisory committee to the Centers for Disease Control and Prevention is expected to debate who should receive booster shots for the Moderna and Johnson & Johnson vaccines, a follow-up to last week’s Food and Drug Administration committee meeting. By the end of this week, if those agencies’ directors approve, many millions more Americans should be eligible to receive additional shots.

By all indications, they are likely to take them. Boosting the Covid vaccines’ effectiveness has turned out to be very popular: According to the CDC, more than 10 million Americans have received third doses since August, a combination of newly approved Pfizer boosters, immunity-bolstering shots for immunocompromised people, and probably some shots given on the sly. Overall, more boosters are being administered now in the US than first doses.

The rush for boosters, likely to intensify once the Moderna and J&J shots are cleared, is doing more than just consuming the doses snubbed by Americans who persistently refuse the shots. It is also reframing the purpose of the Covid vaccine—as a hedge against any infection, rather than just preventing illness or death. And despite White House promises that boosting at home won’t diminish the number of doses the US sends abroad, it is setting a model for international priorities in pandemic protection.

“It's naive to say that if you spend those boosters here, that it won't take away from preventing disease and death elsewhere,” says Nahid Bhadelia, a physician and the founding director of Boston University's Center for Emerging Infectious Diseases Policy and Research. “When the US says ‘Boosters for all,’ that means a lot of other countries may take on that stance as well. Which means that the doses available globally will be lower.”

The White House’s announcement this summer of a comprehensive plan for booster shots was controversial. It would have allowed anyone 18 or older who had received two doses of either the Pfizer or Moderna vaccines to receive a third, eight months later. That proposal defied the wishes of the World Health Organization, which had asked rich nations to hold off on booster plans until low-income countries could amass enough doses to start vaccination campaigns. It did nothing to get shots into the unvaccinated, whose vulnerability to infection is the chief driver of the US pandemic. And it appeared to challenge the reasons why the FDA authorized the vaccines last December, which was to prevent severe illness, hospitalization, and death—which, according to data presented to the agency, the inoculations still accomplish.

Five weeks later, the FDA and the CDC blessed a Pfizer booster, but with stricter rules. After an intense discussion over whether the data supported giving one to “every adult,” as President Joe Biden had promised, they limited the shots to people facing specific risks. Those risks included being 65 or older, because the immune system becomes less competent with age; being at least 18 and having an underlying condition; or being at least 18 and working in a high-exposure job. That decision, according to the White House, authorized shots for 60 million out of the 104.5 million Americans who have received two doses of the Pfizer vaccine.

Pfizer went first because its data was ready to go when the administration opened the discussion, but the other companies were not far behind. Last week, the FDA’s advisory panel voted to allow Moderna boosters under the same rules—same eligibility criteria, same timing—for a shot that is half the original Moderna dose. It also authorized a J&J booster for anyone 18 or older, to be given at least two months after the original shot. The CDC’s advisory panel will take up those two new authorizations in a meeting starting Wednesday.

Experts studying the third-shot decisions are concerned the plans are founded on fundamental ambiguities: small data sets that document boosters’ effects in the real world, sparse information on breakthrough infections among vaccinated Americans, and a lack of clarity regarding how much changes in behavior—as opposed to improved immunity—might account for declines in cases in countries where boosters are already being given.

According to the CDC, 69.5 million Americans took the two-shot Moderna formula, and slightly more than 15 million got the single-shot J&J vaccine. If boosters for those vaccines are approved this week, as expected, many millions more doses could thus be given in the US.

Ethicists find this simply dismaying. “The spectacularly unfair distribution of vaccines around the globe violates our duty to the least well-off,” says Nancy Jecker, a bioethicist and professor at the University of Washington School of Medicine, and coauthor of a new paper on vaccine equity in the Journal of Medical Ethics. “Just 2.5 percent of people in low-income nations have received at least one dose of vaccine. Before making the well-to-do better off, we ought to bring everyone up to a threshold level of protection.”

The US is by no means alone in its pursuit of boosters. France, Germany, Sweden, the United Kingdom, Israel, and the United Arab Emirates have all opened booster shot campaigns to large numbers of their residents, or announced plans to do so. But campaigns intended to protect the most vulnerable have had a tendency toward mission creep, Jecker points out, consuming more doses than first planned, and sharpening global inequity. “In July in Israel, those age 60 and over became eligible for booster shots,” she says. “A month later, everyone 50 and over lined up. And then on August 29, Israel began offering boosters to healthy young adults.” The data behind that nation’s decisions, which was presented to the FDA, showed that mild and moderate infections appeared to be increasing among Israelis (all of whom received the Pfizer vaccine).

Over the past few weeks, members of the US advisory committees that met to evaluate boosters proposals, first for Pfizer and then for Moderna and J&J, have seemed uncertain how broadly extra shots should be distributed. “We do hear, very loud and clear, the need for benefit-risk considerations,” Peter Marks, a physician and director of the FDA’s Center for Biologics Evaluation and Research, told that agency’s advisory committee last week after a contentious discussion over the proposed Moderna booster. “The problem is, we don’t know what we don’t know. There are models that predict that we could potentially have another wave of Covid-19 as people go inside this winter, and we have either the current variant, or another one come up.”

Reframing the purpose of a booster from preventing disease to blocking any infection moves the goalposts of the vaccine campaign. Some experts consider that justifiable, given all the problems vaccination has encountered: slow roll-out, stubborn resistance to taking the shots, controversy over masks and mandates, and hospitals overwhelmed with severely ill unvaccinated people. “If you reduce even a little bit of transmission now, when community transmission is so high, you could have an influence on the course of the pandemic,” Bhadelia says. But if community levels of immunity improve, she continues, protecting people against infection as well as severe illness, “might not always be our end goal.”

One reason boosters feel controversial is because, well, they have been billed as boosters— unpredicted additions to the regimens tested in the 2020 clinical trials. But it’s possible that those trials, performed under the pressure of needing a vaccine as soon as possible, could never explore how many doses would provide optimal protection. What this year’s real-world data on waning immunity may be showing us is that the Covid vaccines should always have been a longer series.

Among childhood vaccines, this would be par for the course. Many of the first vaccines we receive—against hepatitis B, diphtheria-tetanus-pertussis, Haemophilus influenzae B, pneumococcus, and polio—arrive in three and sometimes four doses. They are spaced months or more than a year apart, to allow the immune system to build up as much protection as it can before the next dose stimulates it again.

Government communication about the pandemic has been so confused—masks are pointless, masks are essential; surfaces are hazardous, no, wait, airborne particles are the real danger; boosters are for everyone, well, maybe not—that changing any more messaging feels like a risk. But some experts feel that reframing the mRNA vaccines as a three-dose series would make more sense. It would normalize what is now an addition, making it an expected part of the vaccination process. It might keep the vaccine-hesitant from feeling like one more shot is being forced on them. And it could allow for reevaluation of the time period over which those three shots are given, a change that might increase the protection they offer, without adding yet more shots to the mix.

“I feel very strongly that we should be rethinking the timing of how the shots are administered,” says Monica Gandhi, a physician and infectious diseases professor at UC San Francisco. She points out that both Canada and the UK chose to delay giving second doses in order to achieve the partial protection of a first dose in as many residents as possible. That gamble paid off: Researchers in British Columbia and Birmingham have found that delaying a second dose long as 12 weeks, compared to the three weeks the clinical trials specified, created much higher antibody levels afterward.

Perhaps this all seems moot: With the pace of first-dose administration slowing so dramatically in the US, it might seem too late for reconceptualizing how we frame or deliver the shots. But in fact, a whole new vaccination campaign is about to start. Approval for giving the vaccines to children younger than 12 could arrive by mid-November, and in multiple polls, at least 40 percent of parents have said their children will get the shots.

"This is exactly the time to start discussing spacing for how we get the best effectiveness,” Gandhi says. “It's not too late to change, in the sense that we still have this whole bunch of people that we have to vaccinate.”