- People vaccinated with one of the three coronavirus shots authorized in the U.S. could benefit from receiving a different booster dose than their first, a study run by the National Institutes of Health and published online Wednesday found, offering important new data for public health officials and regulators.
- In the study, which enrolled about 450 people who had been vaccinated with either Pfizer's, Moderna's or Johnson & Johnson's vaccine, an additional dose of any of the three shots spurred many times higher immune responses. While there are major limitations, including the study's size and follow-up, the data suggest a more flexible approach to booster doses may be possible.
- Results come one day before advisers to the Food and Drug Administration begin a two-day meeting to debate whether to recommend authorization of booster doses of Moderna's and J&J's vaccines. The FDA cleared a booster of Pfizer's for many Americans on Sept. 22.
Scientists at the FDA and Centers for Disease Control and Prevention have been grappling with the question of who needs an additional vaccine dose, and when, for weeks now.
The authorization of a third dose of Pfizer and BioNTech's vaccine for certain groups in late September left without guidance tens of millions of Americans who received either Moderna's or J&J's shot for their initial vaccination. CDC data shows that nearly 9 million Americans have received a booster shot to date, although it does not distinguish whether they were part of groups authorized to receive one. Reports indicate Americans across the country are seeking out boosters even if one is not yet recommended for them.
In the NIH study, 458 volunteers who had been fully immunized with either Pfizer's, Moderna's or J&J's shot were given a booster four to six months after completing their initial vaccine regimen. They were divided into groups based on the vaccine they first received, then given either a matching booster from the same developer or a shot from one of the other two.
In all cases, the additional dose increased antibody levels against the coronavirus, a change that's generally associated with greater protection from COVID-19.
But results suggested a boost from the mRNA vaccines from Moderna and Pfizer spiked antibody levels by much higher than did J&J's. This was particularly the case for people who received J&J's vaccine initially and had lower levels to begin with. Volunteers who got Moderna or Pfizer's two-dose regimen and received either of those two for an additional dose had more closely comparable antibody levels afterwards.
Notably, however, the Moderna dose used in the study was the 100 microgram dose currently authorized, rather than the 50 microgram dose the company has requested be cleared as a booster shot.
There were other limitations, too. Participants were not randomized, nor segmented based on the time from last vaccination. Researchers further noted that the follow-up period was too short to detect rarer or late-emerging side effects from booster doses. It's also not yet clear for how long an increase in antibody levels might drive higher protection following a third dose.
"These data suggest that if a vaccine is approved or authorized as a booster, an immune response will be generated regardless of the primary Covid-19 vaccination regimen," the researchers wrote. Their work has not yet been peer-reviewed and was made available online on the "pre-print" server medRxiv.
A third dose of Pfizer's vaccine is currently authorized six months after the first two for adults over 65, younger adults with underlying medical conditions and individuals older than 18 whose "frequent institutional or occupational exposure" puts them at higher risk of contracting severe COVID-19. Immunocompromised people are also eligible for a third dose of either Pfizer or Moderna's vaccine, although in that case the extra shot is because they are less likely to have had a sufficient immune response with two.
On Thursday and Friday, the FDA's advisory committee will discuss authorizing boosters for Moderna and J&J vaccine recipients more widely. Moderna requested a clearance that matches what's been authorized for Pfizer's shot, while J&J is asking for booster authorization for people over 18 years old.
The committee will hear from the NIH about the results of boosting study on Friday, though at that point, they will have already voted on their recommendations, according to the meeting schedule.