FDA advisers vote to endorse Moderna's COVID-19 vaccine booster shots

An outside panel of the Food and Drug Administration's vaccine experts voted unanimously to endorse Moderna's request to roll out booster shots of its COVID-19 vaccine for older and higher-risk adults who were vaccinated at least six months ago. The vote follows an hours-long meeting discussing the safety and need for an additional dose. 

Most studies currently suggest the vaccine remains highly effective at protecting most people against severe COVID-19 infections and death. However, members of the FDA's Vaccines and Related Biological Products Advisory Committee agreed with Moderna and federal health officials who argued that a third, smaller dose should be authorized to boost protection against breakthrough infections in the face of the highly contagious Delta variant, combined with a looming flu season experts warn could be unusually severe for hospitals.

The committee supported boosters for people age 65 and over; those over 18 with medical conditions that put them at higher risk of severe illness from COVID-19; and people whose occupations or institutional residences put them at higher risk of exposure.

FDA officials said they planned to model Moderna's authorization on Pfizer's, which was "designed to allow for flexibility" in making the vaccine available for Americans "where the benefit would outweigh the risks," even if they were not likely to face severe infections of COVID-19. However, the agency said the authorization could be fine-tuned based on the panel's feedback. 

"We do need to account for the fact that mild to moderate COVID-19 can be associated with adverse outcomes such as blood clots and long COVID-19, even in those who have breakthrough infections," the FDA's top vaccine official, Dr. Peter Marks, told the committee. 

The FDA and CDC authorized Pfizer's third shot for older and higher-risk Americans last month. More than 7.3 million vaccinated people have received a booster shot of Pfizer's vaccine, according to the Centers for Disease Control and Prevention. Around 1.5 million have received a third dose of Moderna's vaccine, which only some immunocompromised Americans are eligible to receive for now. 

The FDA's Vaccines and Related Biological Products Advisory Committee is scheduled to reconvene Friday on Johnson & Johnson's request to give a second dose to some "high risk" Americans as early as two months after they were first vaccinated with the single-shot vaccine.

"To the extent that we can try to harmonize between the various vaccines to the greatest extent, we greatly appreciate that, because in the practice of rolling things out, we think that will make things easiest and create the least confusion," Marks said. 

This week's meetings are just a key first step in the process of allowing booster doses for Moderna and Johnson & Johnson. State and local health officials are planning for the possibility that Moderna and Johnson & Johnson's booster shots could be fully green-lit as early as next week. 

After the advisory panel's votes, the FDA is expected to move quickly to decide on formal authorizations for the booster shots. But before additional shots can be given, the CDC must also first issue guidance that would allow their use. The CDC's Advisory Committee on Immunization Practices is scheduled to meet on Thursday next week to discuss COVID-19 vaccines.

The Biden administration has already moved to prepare vaccinators to begin administering Moderna's booster shots, which the company says should come in a 50 microgram dose at least six months after adults were first vaccinated. From their current stock of vaccine, providers will be able to simply draw up half of the 100 microgram doses that made up Moderna's first two shots.

While health officials have voiced concern over possible logistical challenges to having smaller dose sizes, Moderna's Dr. Jacqueline Miller told the panel they "believe we should vaccinate with the lowest amount of antigen needed" while still achieving high vaccine efficacy. Shrinking the booster shot "would also increase the worldwide vaccine supply" of Moderna's doses, Miller said. 

Like with Pfizer's booster shots, Moderna said its trial data show that side effects from its proposed third dose would likely be similar to the second dose. The company's study of the booster shot turned up no cases of myocarditis or pericarditis, the rare but potentially serious cases of heart inflammation that have been seen in a small number of people who received Pfizer and Moderna's vaccines. 

"In order to assess for rare adverse reactions, such as myocarditis, one would really need a significantly larger safety database by orders of magnitude. And that is really for post-authorization surveillance to address," the FDA's Dr. Doran Fink told the panel. 

Health officials from Israel also presented to the panel, saying there was "no question" their nationwide Pfizer booster shot rollout had curbed the Delta variant's surge there earlier this year, while turning up no new serious safety concerns. However, they cited forthcoming research suggesting that not all vaccinated Israelis may have needed a booster shot.

"When we are talking about breakthrough, meaning that they had at least one dose and then also got infected and then recovered, we see that they have a very good protection overall," the Weitzman Institute's Dr. Ron Milo told the panel, saying their immunity appeared "similar" to those with a third shot.

Though the pace of new cases, hospitalizations, and deaths from COVID-19 have declined from their latest peak in the U.S., federal health officials have warned that transmission of the virus remains at dangerous levels as the country approaches "a potentially severe flu season this year" — raising concerns about a potential "twindemic." More than 86% of counties nationwide remain at "high" transmission of COVID-19, according to the CDC's tally.

Tomorrow, after voting on Johnson & Johnson's booster shot request, the panel is also expected to get a presentation from scientists on the findings of a clinical trial backed by the National Institutes of Health that tested mixing-and-matching COVID-19 booster shots from different manufacturers.

Data from the study, which was released Wednesday as a preprint that has yet to be peer-reviewed, suggest it could be safe and effective to administer what's called a "heterologous" boost for most people. For example, recipients of Johnson & Johnson's vaccine who received Pfizer's booster shot saw antibodies reach levels correlated with high vaccine efficacy and turned up no safety concerns. 

"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 study's authors wrote.