Dr. Hana Mohammed El Sahly, a molecular virology and microbiology expert at Baylor College of Medicine, is not one of those researchers—and she says she wouldn’t recommend that course of action. “Until we have better data, it probably is not wise to go and get [additional] vaccines unless it’s part of a clinical trial,” she says. Those data are on the way. National Institutes of Health (NIH) scientists study what happens when people get a booster of a different vaccine than their original shot. That study includes the Johnson & Johnson vaccine.
European research teams have also published results suggesting that it’s practical to mix one dose of Pfizer-BioNTech’s vaccine with one dose of the shot made by AstraZeneca-Oxford University—like Johnson & Johnson’s vaccine, which s adenovirus-based. That’s not a direct parallel, but it does support the general concept of mixing and matching doses. Countries including Germany, Canada, and the Dominican Republic are already trying out such systems, but none are mixing Johnson & Johnson shots with other vaccines.
Safety aside, a second shot might not even be necessary. A new study published in Nature found that people only partially vaccinated people who received only one shot out of a two-dose regimen) were susceptible to the Delta variant. Still, fully vaccinated individuals were much better protected. The study didn’t analyze Johnson & Johnson’s shot, but people who get the one-dose vaccine are considered fully vaccinated by the CDC. Johnson & Johnson says its vaccine-like others authorized in the U.S.—works well against the Delta variant, although that conclusion came from a microscopic study. Even with the Delta variant spreading, El Sahly notes, most people who end up hospitalized or die from COVID-19 are unvaccinated, suggesting the shots continue to work well as authorized.
If you’re concerned, El Sahly says your best bet, at least for now, is returning to precautions like masking and social distancing—not getting the second type of vaccine. That advice may change down the road. Experts have said everyone may need a booster shot roughly a year after vaccination, depending on how long they protect against the virus. By the time health officials know whether boosters are necessary, El Sahly says, researchers will hopefully have gathered enough data to recommend whether you should stick with Johnson & Johnson or switch to Pfizer-BioNTech or Moderna. And if you’re desperate to get double-vaccinated, the NIH’s study on mix-and-match dosing is enrolling now. “You can volunteer there and help us generate those data,” El Sahly says.
