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They also rejected other ideas to stretch the vaccine supply, and said people who speculate on whether to stick to just one dose or cut doses in half are misinterpreting the data.
“These are all reasonable questions to consider and evaluate in clinical trials. However, at this time, suggesting changes to the dosage or FDA-approved schedules of these vaccines is premature and not firmly grounded in the evidence. Without adequate data to support these changes in vaccine delivery, we run a significant risk of endangering public health, undermining historic vaccination efforts to protect the population against COVID-19, ”said they added.
Senior Operation Warp Speed adviser Moncef Slaoui told CNN on Sunday that the FDA would consider giving half-doses of Moderna’s Covid-19 vaccine to people between 18 and 55 – which could make the vaccine available to twice as many people in this age group.
Slaoui said previous data shows the vaccine appeared to elicit effective antibody responses in volunteers under 55 who received either the full 100 microgram dose or a half dose. While an FDA backgrounder last month also referred to these “comparable” immune responses from Moderna’s Phase 2 study, the full data has yet to be released.
But Marks and Hahn said those results covered only a very few people who weren’t followed for long to see if their immune responses were sustained over time.
“What we’ve seen is that the data from companies’ submissions for the first dose is often misinterpreted. In the phase 3 trials, 98% of the Pfizer-BioNTech trial participants and 92% of the Moderna trial participants received two doses of the vaccine three or four weeks apart, respectively, ”they wrote. .
“Participants who did not receive two doses of the vaccine three or four weeks apart were generally followed for only a short time, so we cannot conclude anything definitive about the depth or duration of the vaccine. protection after a single dose of vaccine based on the percentages of single doses declared by the companies. “
British officials have said they will allow more than 21 days between doses of Pfizer’s vaccines and consider allowing people to get vaccinated with two different vaccines. Hahn and Marks rejected these ideas for the United States.
“The available data continue to support the use of two specific doses of each licensed vaccine at specified intervals. For Pfizer / BioNTech COVID-19 vaccine, the interval is 21 days between the first and second dose. And for the Moderna COVID-19 vaccine, the interval is 28 days between the first and second dose, ”they wrote.
It’s understandable that people want to increase the vaccine supply, they said. But this is not advised.
“If people are not sure how protective a vaccine is, there is a risk of harm because they can assume that they are fully protected when they are not and, accordingly, change their behavior to take unnecessary risks, ”they said.
Dr Paul Offit, an infectious disease specialist at the University of Pennsylvania, told CNN he thinks halving vaccine doses is a bad idea.
“There is no data on the effectiveness of a half dose. If you use a half dose, you are just making it up. You just hope you are right,” added Member Offit. of the FDA’s Vaccines and Related Biological Product Advisory Committee. “Why would you dare to invent something when you don’t know whether it works or not?”
Dr Arnold Monto, who was the committee’s acting chairman at meetings last month to review Moderna and Pfizer’s vaccine applications, told CNN on Monday that reducing the dose would be unusual. “It would be a very unusual step, given 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. from Michigan.
CNN’s Dr Sanjay Gupta and Elizabeth Cohen contributed to this story
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