How to Time Your Second Booster

The effects of the first one may be fading. When will it be time for seniors to re-up?

Black-and-white photo of a woman receiving a COVID-19 vaccine
Justin Sullivan / Getty

Updated at 7:34 p.m. ET on March 15, 2022

Imagine if older Americans had been forced to weather the past three months without the option of a booster shot. Having an additional vaccine dose during the Omicron surge cut seniors’ risks of hospitalization and death by more than 70 percent. But the extra shots still didn’t come close to eliminating risk: Boosted adults ages 65 and older were still hospitalized at nearly twice the rate—and dying at 16 times the rate—of unboosted 18-to-49-year-olds, despite the fact that far fewer seniors were testing positive for the coronavirus.

Given these persistent risks, the possibility of waning immunity, and the apparent onset of a new wave of cases across Europe, even boosted Americans over 65 might be feeling a little nervous. Pfizer asked the FDA to authorize a fourth shot for older people today, and not much is stopping seniors who want to re-boost from doing so already. Whether they ought to is a different matter: Given that COVID rates in the United States are pretty low right now, and that we don’t have a ton of information yet about the value (or potential downsides) of the extra shot, most seniors should probably wait.

As humans age, our immune systems tend to get weaker in the same way that our bones and joints and memories do. That’s why older Americans are more vulnerable to bad outcomes from COVID, and it’s also why they were among the first to be eligible for COVID-vaccine boosters in the fall. Back then, the CDC’s primary motivation for allowing more shots hinged on waning immunity: After several months, the vaccines weren’t doing as good a job at keeping people, and especially older people, from getting sick.

Now, on top of the vaccines’ diminished effectiveness against Omicron, something similar might be happening again. In the United Kingdom, the effectiveness of a third Pfizer dose at preventing symptomatic COVID was shown to fall from 67 to 46 percent within a few months after vaccination. A study published in The Lancet in late February found that blood samples taken from a small group of elderly people showed a steep decline in neutralizing activity against Omicron over the span of three and a half months following a first booster shot. These results are expected and not inherently concerning. What’s more important and less clear is how much, if at all, protection against severe disease and hospitalization is waning.

All of these trends are very preliminary, as are the data on whether adding one more dose actually helps. A yet-to-be-peer-reviewed study of healthy medical workers in Israel who had received a second booster showed an eightfold increase in antibodies against Omicron two weeks after the shot. Among Israelis 60 and older, who have been eligible for a second booster since early January, those who received it were one-quarter as likely as the singly boosted to be hospitalized with severe COVID at the peak of the country’s Omicron surge. But no one can say how long that improved protection will last.

The question of durability might matter more now than it did in the fall. In September, experts were fairly confident that a winter wave was coming; even if the boost lasted only, say, five months, the fresh antibodies of a senior jabbed in October would likely last through the worst of the surge. Today, Omicron is in retreat in the United States (at least for now), and we’re eight-ish months away from the next possible winter surge, and four-ish months from a summer surge that would match the ones in 2020 and 2021. But pandemic protections are dropping around the country, and cases in Europe, which have sometimes been a harbinger for the U.S., appear to be on the rise. Who’s to say we won’t find ourselves in the middle of another surge any minute now? Such uncertainties make it much harder to predict now when older Americans might need an additional booster shot, because doing so would mean predicting the timing of the next peak in cases.

Faced with this dilemma, a COVID-conscious senior might be tempted to boost now, while their immunity might be low, and just grab another shot in a couple of months if cases start to swing back upward. But such a plan could backfire. John Wherry, an immunologist at the University of Pennsylvania, told me that boosting too often with the original-recipe vaccine—the only kind that’s available in the U.S. right now—could lead a person’s immune system to react to newer, less similar variants such as Omicron with reduced vigor. Plus, something better could be right around the corner. Pfizer and Moderna are testing Omicron-specific boosters—though the underwhelming preliminary results make Wherry think that those shots in particular are not worth holding out for. He’s more excited about the possibility of mucosal vaccines and the eventual arrival of Novavax’s protein-based shot, which has a promising efficacy and safety profile but is still awaiting the FDA’s green light. One of these alternative designs may end up being a better match for the mature immune system. (A protein-based shot, for example, is nearly twice as effective as a live-attenuated vaccine at preventing shingles in seniors.) The only way to know whether older people respond better to a different sort of vaccine will be to test it, Mark Slifka, an immunologist at Oregon Health and Science University, told me. “You need to cater to each particular bug.”

A fourth shot, then, might give seniors more protection for an unknown period of time against a disease that is currently in decline in the U.S., and it might jeopardize some of their protection against that same disease when cases begin to rise again. Lona Mody, a geriatrician at the University of Michigan, told me that she doesn’t think we have enough data yet to recommend second boosters to seniors across the board. But if one of her patients felt that they needed one—say they have a family event coming up where they’ll be inside with lots of people, some of whom might not be vaccinated—“I would definitely consider it,” she said. Slifka agreed that these decisions should be made in consultation with a doctor, and in consideration of whether a particular senior lives alone or in a congregate setting, their general health, and whether they have a high-exposure job.

Wherry said he’d like to see a national surveillance system for COVID immunity, in which Americans could get periodic immunity checkups on their antibody levels and learn whether boosting would do anything for them. “This is feasible, both scientifically and medically,” he said. And by studying the resulting data, the CDC could make more informed decisions about when (or whether) to recommend boosters for everyone. For the moment, though, unless you’re at particularly high risk of getting COVID because of where you live or work, there’s really no rush.