Pfizer Says It's Unknown If Covid-19 Protection Holds After Single Vaccine Dose

Pfizer Inc. said the second dose of its Covid-19 vaccine should be delivered to individuals within the recommended 21-day period, calling into question a decision by the U.K. to space out the dosing regimen.

The U.K. decision not to hold back any of its vaccine supply is aimed at quickly reaching as many high-risk people as possible. Under the government plan, second doses could be administered as many as 12 weeks later, longer than the three-week timing determined as optimal by Pfizer’s late-stage studies and the four weeks suggested for the shot developed by Moderna Inc.

People should get their shots on the recommended schedule, Pfizer said on Thursday, warning “there is no data to demonstrate that protection after the first dose is sustained after 21 days.”

Information on the efficacy surrounding a single dose has been misinterpreted, said Peter Marks, director of the U.S. Food and Drug Administration’s office that oversees vaccines. Relying on one shot, he said, “is concerning.”

“If people do not truly know how protective a vaccine is,” Marks said in an email, “there is the potential for harm, because they may assume that they are fully protected when they are not and alter their behavior to take unnecessary risks.”

Marks’ comments come as the British Medical Association said on Thursday that the U.K.’s decision would require doctors to reschedule appointments for tens of thousands of elderly and vulnerable patients to get their second vaccine doses. The group called the move “grossly unfair.”

Anthony Fauci, the top U.S. infectious disease expert, also weighed in on the U.K.’s decision in an interview on NBC’s Today Show on Thursday. Spreading out the two doses is “under consideration,” he said, though he didn’t specify by who.

“I still think, if done properly, you can do a single dose, reserve doses for the second dose, and still get the job done,” Fauci said. But he added “you can make an argument, and some people are, about stretching out the doses and giving a single dose across the board and hoping you’re going to get the second dose in time to give to individuals.”

In its statement, Pfizer said surveillance is needed on any alternative vaccination schedules, and that authorities should work to ensure each recipient is afforded the maximum possible protection.

“Data from the Phase 3 study demonstrated that, although partial protection from the vaccine appears to begin as early as 12 days after the first dose, two doses of the vaccine are required to provide the maximum protection against the disease, a vaccine efficacy of 95%,” Pfizer said in its statement.

An FDA document of frequently asked questions on Pfizer and partner BioNTech SE’s vaccine notes that the agency’s assessment of the safety and effectiveness of the vaccine was based on data on patients who received two shots three weeks apart.

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