Since it was the last COVID vaccine to be authorized for emergency use in the United States, J&J’s six-month data on the shot’s efficacy has only just appeared this week. The study was released pre-print (which means that it has yet to be peer-reviewed) on September 10.
The study looked at vaccine efficacy anywhere from 14 days after vaccination to 152 days after vaccination, finding no meaningful variation over that timespan. On average, the Johnson & Johnson vaccine appears to be 79% effective against COVID-19. But more research is needed on longer term effectiveness.
On September 21, J&J released a statement regarding the efficacy of its booster shots, which is part of the ongoing study on the vaccine’s safety and efficacy.
Preliminary data show that when administered two months after the first shot, the J&J booster has a 94% efficacy rate against moderate to severe COVID infection and 100% efficacy against severe to critical infection. When the time between shots is longer, the booster may be even more effective; data showed a 12-fold increase in antibodies when the booster was administered six months after the first shot.
Do I Need a J&J Booster?
Many people who got the one-shot J&J vaccine—even those who do not have compromised immunity—are expecting to need a booster eventually. However, Sri Banerjee, MD,PhD, MPH, FACE, a faculty member at Walden University’s PhD program in Public Health, tells Verywell that while booster shots are likely, they should not be assumed.
“Giving boosters to the immunocompromised is a no-brainer,” Banerjee says. “But the caveat is that all the studies have measured is neutralizing antibodies. When it comes to other aspects of immunity, we have no clue what’s going on there.”
The ambiguity in the study results means that the Food and Drug Administration (FDA) has proceeded more cautiously than first expected when authorizing boosters. Banerjee says that from a public health standpoint, prioritizing unvaccinated people is still more important than boosters for the general population.
The Centers for Disease Control and Prevention (CDC) anticipates authorizing boosters for people who received the J&J shot, but it has not hinted at when that might happen. It took several weeks after Pfizer released its booster results for the shot to get authorization.
Can I ‘Mix and Match’ COVID Shots?
For immunocompromised people, J&J’s efficacy numbers may not be as reassuring as the efficacy rates demonstrated in the Pfizer or Moderna vaccine data. The Pfizer and Moderna vaccines offer higher initial efficacy rates around 95%, but the one-dose Johnson & Johnson vaccine still demonstrates a 79% efficacy against infections and an 81% effective rate against hospitalization.
Even among people who do not have a compromised immune system, there has been a question of whether a “mix and match” booster strategy—giving one shot of either Pfizer or Moderna instead of an approved J&J shot—would be safe and effective.
For now, Banerjee says that accepted guidelines advise against the “mix and match” approach.
“You’re trying to boost the effectiveness of the initial shot, so it should be with the original vaccine provided,” says Banerjee, adding that, more importantly, there has been no hard data on the effects of mixing vaccines.
Some countries, including Israel and Germany, have started offering the option. In the U.S., the CDC will not authorize the practice without having data from peer-reviewed studies specific to mixing shots.
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With a booster shot, which will likely be approved in the coming months, the efficacy of the J&J shot will compete with the two-shot series by Pfizer and Moderna.
Currently, experts do not recommend “mixing and matching” COVID doses and are advising J&J shot recipients to be patient.
