After a long and tense meeting today, an FDA committee unanimously recommended that the agency authorize third shots of the Pfizer COVID-19 vaccine for Americans who are over 65 or at high risk of severe COVID. The vote came after the panel voted overwhelmingly against the original question up for its consideration: authorizing boosters for everyone over 16. If the FDA follows the committee’s recommendation (as is expected), a CDC committee will help refine those guidelines next week, clarifying which groups qualify as “high risk.”
Even as we await these final decisions, the nation’s summer wave of COVID infections seems like it’s beginning to pass. Cases and hospitalizations are trending slightly downward. Now that we have more clarity about whether (and which) Americans need booster shots—and given that so many people are already getting boosters, eligibility be damned—more questions loom: When, exactly, should those people get those shots? Is it better to load up on extra antibodies as soon as possible, or should people wait until COVID rates start to rise again?
Here’s a simple starting point: If you’re already eligible for a third shot because you’re immunocompromised, get it on the sooner side. The CDC recommends at least a 28-day wait after your second mRNA dose, while two experts told me that the best window is four to five months after. In many immunocompromised people, the first one or two shots might not have triggered a strong enough response in the body to provide lasting protection. For them, the booster shot isn’t meant to fill in the cracks of your shield against the virus; it’s meant to create that shield in the first place.
Things get squishier for vaccinated people with relatively healthy immune systems. They’ll already be flush with newly minted B and T cells, which lie in wait to produce antibodies and attack the coronavirus. Ali Ellebedy, an immunologist at Washington University in St. Louis, told me that the longer those cells mature in the body, the more prepared they are to fight off the invader. Delivered too early, another dose of the vaccine could end up “restarting something that was already working,” he said. Ellebedy recommended delaying any booster shots by at least six months from your initial course of vaccination. Eight months is better; even a year would be fine.
At the same time, booster shots do increase the measurable level of antibodies in the blood, pretty much whenever they’re received. The clinical benefits of this spike for fully vaccinated people remain unclear, though some preliminary evidence suggests that an antibody surge could reduce your chances of getting sick, or of transmitting the Delta variant to other people—at least until your antibody levels wane once more.
Most people’s antibody levels peak a few weeks after their initial COVID-vaccine shots. If that holds true for boosters, too, then you might be tempted to time your next injection for three-ish weeks before you’d most want to be protected. Maybe the virus surged in your county last December, and you’re afraid it’ll do the same this year—so you decide to get your booster around Veterans Day. Maybe you want to make sure you don’t infect Uncle Dave at Thanksgiving—so you make an appointment for Halloween.
The problem is, “a few weeks” is just an average. Müge Çevik, a virologist at the University of St. Andrews, told me that different people develop antibodies at wildly different rates. In general, young, healthy people’s immune systems work quickly and can start to approach their peak antibody levels in as little as seven days. Older people, or those with compromised immune systems, can take weeks longer. Given that we don’t know how long those spikes last, these differences could be crucial.
Also, predicting when you’ll be in the most danger requires predicting when transmission in your community will be at its highest, which is nearly impossible to do with any precision. “It is very likely we will see another surge” this winter, Saskia Popescu, an infectious-disease epidemiologist at George Mason University, told me, but identifying the specific week or month when cases will peak in a given place just isn’t feasible. (Even a winter surge isn’t a sure bet: “At the moment, we don’t really have a consistent seasonal pattern,” because all of our surges have been shaped by behaviors like masking and distancing, Çevik said.) Popescu also pointed out that the rise of at-home testing and the decline of mass-testing sites could make it harder to detect smaller upward ticks until a surge is fully upon us.
Still, the mere likelihood of a winter surge does make it reasonable to wait, at least a bit. Çevik worries that if a large number of people rush out to get their extra shots, their antibodies will have faded by the time they’re needed most, and a winter surge could see even more breakthrough infections. Çevik advised her own parents, whom she described as being “in clinically vulnerable groups,” to get their boosters at the end of September or in October. Young people with healthy immune systems could stand to wait until November or early December. (This advice comes with exceptions: If you’re, say, a nurse on a COVID ward in a county where cases are spiking, getting a booster now might be prudent.)
Ultimately, the dynamics of transmission in your area may be more important than the details of your personal vaccine schedule. David Dowdy, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, would rather see boosters distributed sparingly and strategically to communities that show signs of an impending surge. While everyone else waits, vaccine makers could update their formulas to better protect against Delta and set up randomized controlled trials to gather better data on how their original doses and boosters are performing.
On an individual level, Dowdy told me, there’s probably minimal harm in eligible people getting third shots now. But vaccine makers might have a new shot in a few months, designed around circulating variants, or even an intranasal option that can stop infections sooner. Once the government announces that tens of millions of people should get a booster now, persuading them to do so again in a few months, when a better option is available, could be difficult. And those who decide to get a booster now might find they’re ineligible for a fourth shot when that better option comes. Case rates might seem scary now, but this pandemic has proved time and again that things can certainly get worse. “I think it’s important to not just say, Should I get a booster or not?” Dowdy said, “but rather, Would I prefer to have a booster now or save the opportunity for later?”
This article previously misstated that the CDC recommends that immunocompromised Americans get a booster shot at least 28 days after a first Johnson & Johnson dose. In fact, the CDC does not currently recommend any booster shots for people vaccinated with Johnson & Johnson.