As governments around the world rush to vaccinate their citizens, scientists and policymakers are debating whether to reserve the second doses everyone will need, or give as many people as possible just one shot now — potentially at the expense of giving second doses on schedule.
A number of countries in Europe are considering the options, or moving forward with the delay, despite a lack of evidence about how much protection a single dose of vaccine will provide and how long it will last.
Denmark on Monday approved a lag of up to six weeks between the first and second shots of the Pfizer-BioNTech vaccine, Reuters reported, although the vaccine is meant to to be given in doses three weeks apart. Germany and Ireland are considering similar moves.
Britain last week announced a plan to separate doses by up to 12 weeks. Britain has authorized Pfizer’s vaccine as well as the product developed by the University of Oxford and AstraZeneca, which is meant to be given in doses separated by four weeks.
So far, health officials in the United States have been adamantly opposed to the idea, saying it is not supported by the data gathered in clinical trials.
“The approach some countries are taking of delaying the booster shot could backfire and could decrease confidence in the vaccines,” Moncef Slaoui, scientific adviser of Operation Warp Speed, the federal effort to accelerate vaccines, said on Sunday night.
In the late-stage clinical trial that found the vaccine from Pfizer-BioNTech to be highly effective, participants generally received their seconds shots about three weeks after the first, although data were included from people who received the doses as far as seven weeks apart. In a statement on Monday, the European Union’s drug regulator, the European Medicines Agency, expressed support for sticking to the original plan for spacing the doses of the vaccine. “Any change to this would require a variation to the marketing authorization as well as more clinical data to support such a change,” said Monika Benstetter, an agency spokeswoman.
Since the United States began rolling out authorized vaccines from Pfizer-BioNTech and Moderna, second shots of the vaccines have been sequestered to guarantee that they will be available for people who have gotten their first injections.
Pfizer has also pushed back on the idea of additional lag time. “Two doses of the vaccine are required to provide the maximum protection against the disease,” said Steven Danehy, a spokesman for Pfizer. “There are no data to demonstrate that protection after the first dose is sustained after 21 days.”
The developers of authorized vaccines have reported that a degree of protection appears to kick in after the first shot of vaccine, although it’s unclear how quickly it may wane.
Still, despite a high-level repudiation of the U.K. strategy from Dr. Anthony S. Fauci, the nation’s top infectious disease expert, some scientists believe the United States should consider widening the gap between doses. Proponents of the idea argue that spreading vaccines more thinly across a population by concentrating on first doses may save lives.
On Sunday, Dr. Robert M. Wachter, the chair of the department of medicine at the University of California at San Francisco, and Dr. Ashish K. Jha, the dean of the Brown University School of Public Health, wrote in an opinion piece in The Washington Post that “it’s time to change the plan.”
“The biggest mistake you can make in medicine is anchoring bias,” Dr. Wachter told The New York Times. “You get stuck on what you thought, and you don’t shift with new information.”
The debate reflects frustration that so few Americans have gotten their first doses.
As of Monday morning, three weeks into the vaccination drive, 15.4 million doses of the Pfizer-BioNTech and Moderna vaccines had been shipped across the United States, but just 4.6 million people had gotten their first shots.
The rollout has been bumpy. In Houston, the Health Department phone system crashed on Saturday, the first day officials opened a free vaccination clinic. In Los Angeles, now a center of the pandemic, Mayor Eric Garcetti said that vaccine distribution was moving far too slowly. In New York, Gov. Andrew M. Cuomo said on Monday that hospitals in the state will now face fines and potentially lose the opportunity to distribute the vaccine if they do not step up the pace of inoculations.
But some experts are not convinced that increasing the gap between doses will solve the problems that have slowed the rollout of vaccines in the United States.
“We have an issue with distribution, not the number of doses,” said Saad Omer, a vaccine expert at Yale University. “Doubling the number of doses doesn’t double your capacity to give doses.”
