From the WebMD Archives

Feb. 19, 2021 –Could one dose of the COVID vaccines protect as well as two? What about delaying the second dose to get more people vaccinated more quickly? Those questions were raised by three new research briefs.

Two of these briefs, one that appeared in The Lancet and another letter in the New England Journal of Medicine, suggested that single dose of the Pfizer-BioNTech vaccine could be around 90% effective between two and four weeks after the first dose. Together with previous findings that a single Moderna vaccine dose provides 92.1% efficacy against SARS-CoV-2 infection, investigators said it’s time to defer the second dose so more people can get protected with the vaccines.

Anthony Fauci, MD, who directs the National Institute of Allergy and Infectious Diseases, weighed in on these findings on Friday, saying the U.S. will stick with a 2-dose strategy for now.

“And the reason is, even though you can get a fair degree of protection after a single dose, it clearly is not durable,” said Fauci at a briefing Friday from the White House COVID response team.

Andy Slavitt, White House senior advisor on the COVID-19 response, said they would need more research to make any changes to vaccine dosing.

“I think we've got the best people in the world looking at this. I feel very confident and they'll look aggressively at these studies, but I think it's important that you let people understand that we're not going to be persuaded by one study that happens to grab headlines,” said Slavitt.

In a letter published in the New England Journal of Medicine, researchers said a single dose of the Pfizer/BioNTech vaccine offers 92.6% efficacy based on the companies’ own data submitted to the FDA.

The second dose adds little short-term benefit, "while high-risk persons who could have received a first dose with that vaccine supply are left completely unprotected," wrote authors Danuta M. Skowronski, MD, of the British Columbia Centre for Disease Control in Vancouver, Canada, and Gaston De Serres, MD, PhD, of the Quebec National Institute of Health, Quebec City, Canada

In addition, correspondence in the Lancet February 18 appeared to further fortify the single dose Pfizer vaccine strategy. Researchers in Israel reported that one dose was associated with 85% protection against symptomatic COVID-19 in an adjusted analysis of more than 9,000 health care workers eligible for immunization.

"Deferral of the second dose of the COVID-19 vaccine will enable more individuals within our high-risk and health care worker priority groups to receive a single dose," Skowronski said. "Since a single dose provides swift and substantial protection exceeding 90%, and a second dose provides little added benefit in the short term, second dose deferral will maximize the benefits of scarce vaccine supply while the pandemic risk remains elevated."

But Fauci said that protection, while good, doesn’t last long.

He pointed out that a second dose boosts by 10-fold the number of neutralizing antibodies made in response to the vaccine.

He said this large increase in antibodies becomes important from the standpoint of circulating virus variants. People who get a booster have a cushion that may help prevent severe disease, even if they're infected by one of the variants that's evolved to escape some of the vaccine's protection.. More antibodies also means the virus has less chance of escaping and creating new variants.

Other experts agreed, saying more data are needed before changing the two-dose regimen. They also point out that the FDA granted emergency use authorization based on the two-dose studies.

" The studies did not actually look at just giving one dose and trying to just go with that," Dial Hewlett Jr, MD, medical director of the Division of Disease Control at the Westchester County Department of Health in White Plains, NY, said today during a media briefing, sponsored by the Infectious Diseases Society of America.

"It may be true that in the short run, one dose might be effective," Hewlett said, "but we don't know how long that this protection will last, and is the second dose going to be adding to that?"

But Skowronski and De Serres wrote that "given the current vaccine shortage, postponement of the second dose is a matter of national security that, if ignored, will certainly 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."