They also rejected other ideas to stretch the vaccine supply and said people who are speculating on whether to settle for just one dose or cut doses in half are misinterpreting the data.
“All of these are reasonable issues to be considered and evaluated in clinical trials. However, at this point, suggesting changes to the dosage or schedules of these vaccines authorized by the FDA is premature and has no solid roots in the available evidence. Without appropriate data to support such changes in vaccine administration, we run a significant risk of putting public health at risk, undermining historic vaccination efforts to protect the population of COVID-19, “they added.
Operation Warp Speed’s chief advisor, Moncef Slaoui, told CNN on Sunday that the FDA would consider giving half-doses of Moderna’s Covid-19 vaccine to people aged 18 to 55 – which could make the vaccine available to twice as many people in that country. age group.
Slaoui said that previous data show that the vaccine appeared to elicit effective antibody responses among volunteers under 55 who received a total dose of 100 micrograms or half a dose. While an FDA briefing document last month also references these “comparable” immune responses from the modern Phase 2 study, the full data has not yet been published.
But Marks and Hahn said that these findings covered only a few people who were not followed for a long time to see if their immune responses maintained over time.
“What we saw is that the data in companies’ submissions on the first dose are being commonly misinterpreted. In phase 3 studies, 98% of the Pfizer-BioNTech study participants and 92% of the participants in the Moderna study received two doses of the vaccine in an interval of three or four weeks, respectively “, they wrote.
“Participants who did not receive two doses of the vaccine over an interval of three or four weeks were generally followed up for a short period of time, so we cannot conclude anything definitive about the depth or duration of protection after a single dose of the vaccine. from the single dose percentages reported by companies. “
British officials said they would allow more than 21 days between doses of Pfizer vaccines and would consider allowing people to be vaccinated with two different vaccines. Hahn and Marks rejected these ideas for the United States.
“Available data continues to support the use of two specified doses of each vaccine authorized at specified intervals. For the Pfizer / BioNTech COVID-19 vaccine, the interval is 21 days between the first and the second dose. And for Modern COVID -19 vaccine, the interval is 28 days between the first and the second dose “, they wrote.
It is understandable that people want to increase the supply of the vaccine, they said. But it is not advisable.
“If people don’t really know how protective a vaccine is, there is the potential for harm because they can assume that they are fully protected when they are not and, consequently, change their behavior to take unnecessary risks,” they said.
Dr. Paul Offit, an infectious disease specialist at the University of Pennsylvania, told CNN that he thought cutting the vaccine doses in half was a bad idea.
“There is no data on the effectiveness of half a dose. If you use half a dose, you’re just making it up. You just hope you’re right,” added Offit, a member of the FDA Vaccines and Related Biological Products Advisory Committee. “Why would you dare to invent something if you don’t know if it works or not?”
Dr. Arnold Monto, who was acting chairman of the committee during last month’s meetings to consider modern and Pfizer vaccine applications, told CNN on Monday that cutting the dose would be unusual. “This would be a very unusual step, given the fact that it was not studied in Phase 3, but emergency use is also a very unusual step,” said Monto, professor of epidemiology at the University of Michigan.
Dr. Sanjay Gupta and Elizabeth Cohen of CNN contributed to this story