Millions more Americans are now eligible for a booster dose of a coronavirus vaccine, with the Food and Drug Administration announcing Wednesday evening expanded authorizations for both Moderna's and Johnson and Johnson's shots.
The decision to clear an additional dose of both vaccines comes one month after the regulator did the same for Pfizer and BioNTech's shot and reflects concern that the strong protection they produce may be waning, particularly among vulnerable groups.
The FDA also said booster shots could be given interchangeably, regardless of which vaccine a person initially received. The authorization of such a "mix-and-match" approach could be important for recipients of J&J's one-shot vaccine, who recent testing showed might benefit more from getting a booster of Pfizer's or Moderna's vaccines.
While COVID-19 case counts have fallen in recent weeks, hospitalizations and deaths remain well above their recent lows in July. Health officials hope booster doses, which spur higher levels of virus-fighting antibodies, will strengthen immunity and curb the number of breakthrough infections.
"The available data suggest waning immunity in some populations who are fully vaccinated," acting FDA commissioner Janet Woodcock said in a statement. ;"The availability of these authorized boosters is important for continued protection against COVID-19 disease."
The FDA did not recommend a specific pairing of primary vaccine and booster, although advisers to the Centers for Disease Control and Prevention might offer more detailed guidance on Thursday.
For Moderna's vaccine, which is initially given via two doses, the FDA authorized a third shot at least six months after the second for people over 65 and those who are at higher risk of COVID-19 because of medical conditions or their jobs. The clearance matches that granted to Pfizer's vaccine and aligns with the recommendation given by a group of outside advisers to the FDA last week.
In that meeting, Moderna executives presented data showing that antibody levels raised by an initial two-dose regimen decreased over time, but could be elevated substantially higher by a third dose. For that third shot, however, Moderna applied for and the FDA authorized a dose half the size of the first two.
Adults over 18 who previously received J&J's vaccine, meanwhile, are now eligible to receive a second dose at least two months later. The shorter interval between doses reflects evidence from a large clinical trial run by the drugmaker that found two shots spaced two months apart are much more effective at preventing moderate-to-severe COVID-19.
Roughly 15 million Americans have received J&J's vaccine to date, compared to about 70 million who got two doses of Moderna's and 105 million who got two doses of Pfizer's.
J&J's vaccine technology is different than the messenger RNA used by Moderna and Pfizer in their vaccines. Although J&J originally envisioned a one-dose regimen to be a selling point, FDA advisers questioned at least week's meeting whether two doses should now be considered standard. Clinical testing and real-world studies have shown one dose of J&J's shot to be less effective than full regimens of Pfizer's and Moderna's vaccines.
"I think this frankly was always a two-dose vaccine," Paul Offit, director of a vaccine center at the Children's Hospital of Philadelphia, said during the meeting.
Advisers also supported mixing booster doses, particularly for people who initially received J&J's shot. Preliminary data from a study run by National Institutes of Health researchers suggested J&J recipients would be better off with a boost from an mRNA vaccine.
The FDA took note of that data in its decision, stating that the "known and potential benefits" of mixing boosters outweigh the possible risks.
The agency's authorizations Wednesday are one of many significant decisions the agency has been asked to make in recent months, with more still to come. Later this month, the FDA's advisory committee is set to discuss the authorization of Pfizer's vaccine for kids aged 5 to 11 years old. Additionally, there are reports the FDA is strongly considering authorizing booster shots for everyone above the age of 40, though they may not take action until next month.
On Wednesday, the Biden administration laid out its plans for rolling out vaccines for kids, pending FDA authorization and a recommendation from the CDC.