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A single dose of the Pfizer / BioNTech vaccine provides 92.6% efficacy in new calculations based on data submitted to the U.S. Food and Drug Administration (FDA), researchers report.
Along with previous findings that a single dose of Moderna vaccine provides 92.1% efficacy against SARS-CoV-2 infection, researchers suggest it is time to delay the second dose to protect more people through mRNA single dose vaccinations.
Danuta M. Skowronski, MD, of the British Columbia Center for Disease Control in Vancouver, Canada, and Gaston De Serres, MD, PhD, of the Quebec National Institute of Health, Quebec City, Canada, wrote a letter that was published Feb. 17 published in The New England Journal of Medicine
However, other experts disagree, saying more data is needed before deviating from the two-dose regimen that has been evaluated in clinical trials. They also point out that the FDA has granted emergency use approval based on the two-dose studies.
Stick with the studies
Dr. Dial Hewlett Jr
“One of the things we have to consider here is that when these vaccines are tested in clinical trials, they are tested under specific conditions. In this case, two doses were used to achieve efficacy. The studies didn’t really look at giving of one dose and try to go with that, ” Dial Hewlett Jr, MD, medical director for the Division of Disease Control at Westchester County Department of Health in White Plains, New York, said today during a media briefing sponsored by the Infectious Diseases Society of America.
Dr. Matthew Zahn
Matthew Zahn, MD, who also spoke at the IDSA briefing, agreed. “The CDC has worked very hard to give a premium to adhering to what is known science, and the studies looked at two vaccine doses less than 6 weeks apart.
“That’s really why we’ve maintained that recommendation. For my part, I think it makes a lot of sense,” said Zahn, medical director in the Division of Epidemiology and Assessment, Orange County Health Care Agency, Santa Ana, California.
In their correspondence, the authors report that they examined documents submitted to the FDA from 2 weeks after the first dose to the second immunization. They note that “even before the second dose …[the vaccine] was very effective. “
Do two doses extend protection?
Even if the effectiveness of one dose is above 90% initially, the question remains how long that protection will last without a second dose, says Hewlett, who is also a member of the National Medical Association COVID-19 Task Force on Vaccines and Therapeutics .
“We don’t have any research data to say the vaccines will be as effective if you extend the time between the two doses,” said Zahn, who also serves as a liaison representative to the CDC’s Advisory Committee on Immunization.
Other researchers reported a 94.8% efficacy against SARS-CoV-2 after two doses of the Pfizer / BioNTech vaccine in a previous study. The same report estimated the efficacy of a single dose of 52.4% between the first and second dose, “but in their calculation they included data collected during the first 2 weeks after the first dose, when immunity would still be increased “, Skowronski and De Serres note.
“There may be uncertainty about the duration of protection with a single dose, but the administration of a second dose within 1 month of the first, as recommended, provides few additional benefits in the short term, while subjects at high risk that first dose of that vaccine stock is left completely unprotected, “they note.
“It may be true that one dose could be effective in the short term,” admitted Hewlett, “but we don’t know how long this protection will last, and will the second dose contribute to it?” He explained that many public health officials want to simplify the administration of vaccines, but “before we can support this, we will need data that looks at this.”
Skowronski and De Serres conclude their letter by stating that “given the current vaccine shortage, delaying the second dose is a matter of national security that, if ignored, will surely result in thousands of COVID-19-related hospitalizations and deaths this winter in the United States – hospitalizations and deaths that would have been prevented with a first dose of vaccine. “
Skowronski has not disclosed any relevant financial relationships. De Serres reported grant from Pfizer for an unrelated study of meningococcal antibody seroprevalence.
N Eng J Med. Published online February 17, 2021. Correspondence
Damian McNamara is a staff journalist based in Miami. It covers a wide variety of medical specialties, including infectious diseases, gastroenterology and intensive care. Follow Damian on Twitter: @MedReporter
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