I got the Johnson & Johnson vaccine, which booster should I get?

As the omicron variant quickly spreads, Americans are getting booster shots of COVID vaccines at a record pace—last week, nearly 7 million people got boosters. For most people, it’s their third shot. But for the smaller group of people who started with the Johnson & Johnson vaccine, it’s only their second. Does that mean that J&J recipients are less protected?

Not necessarily, says Michael Lin, an associate professor of bioengineering and neurobiology at Stanford University, who performs research on SARS-CoV-2 antiviral drugs and posted a helpful Twitter thread walking J&J recipients through the data in a preprint NIH study. “The answer depends on which boosters you’re comparing,” he says. In terms of peak antibodies, Johnson & Johnson plus Pfizer, he says, is as good as three doses of Pfizer. J&J plus Moderna also performs well. Someone who gets two doses of J&J, on the other hand, is less protected than a Pfizer or Moderna recipient who got a booster.

The NIH study happened before the omicron variant was identified, so it still isn’t clear how combinations of vaccines will respond to it compared to earlier variants. Johnson & Johnson is also currently studying how well its vaccine protects against omicron, but hasn’t yet released data. Pfizer and its partner BioNTech, however, say that while two doses of the Pfizer-BioNTech vaccine produce fewer antibodies in response to omicron, a lab test showed that three doses could neutralize the variant, an early sign that booster shots could be very helpful. People who got J&J plus one of the mRNA vaccines may have similar levels of protection.

“I would say, at the moment, there’s no urgent worry,” Lin says. “If they were boosted by Pfizer, they were boosted fairly recently; for most people, in the last month or two. So their antibody levels are still high. It’s still fresh. It’s similar to people who were triple Pfizer. And we know that that gives some protection against omicron.”

It’s still too early to know how long that protection may last, and when another booster may be recommended—or whether the next shot may be tailored to omicron specifically, something that vaccine developers can do quickly, and a process that’s already underway.