The prospect of a fourth wave of the coronavirus, with new cases climbing sharply in the Upper Midwest, has reignited a debate among vaccine experts over how long to wait between the first and second doses. Extending that period would swiftly increase the number of people with the partial protection of a single shot, but some experts fear it could also give rise to dangerous new variants.
In the United States, two-dose vaccines are spaced three to four weeks apart, matching what was tested in clinical trials. But in Britain, health authorities have delayed doses by up to 12 weeks in order to reach more people more quickly. And in Canada, which has precious few vaccines to go around, a government advisory committee recommended on Wednesday that second doses be delayed even longer, up to four months.
Some health experts think the United States should follow suit. Dr. Ezekiel J. Emanuel, a co-director of the Healthcare Transformation Institute at the University of Pennsylvania, has proposed that for the next few weeks, all U.S. vaccines should go to people receiving their first dose.
“That should be enough to quell the fourth surge, especially in places like Michigan, like Minnesota,” he said in an interview. Dr. Emanuel and his colleagues published the proposal in an op-ed on Thursday in USA Today.
10 days after the first dose, researchers could see that the volunteers were getting sick less often than those who got the placebo.
In the same month, Britain experienced a surge of cases caused by a new, highly transmissible variant called B.1.1.7. Once the British government authorized two vaccines — from Pfizer-BioNTech and AstraZeneca — it decided to fight the variant by delaying the second doses of both formulations by 12 weeks.
said on Jan. 31 on NBC’s “Meet the Press.”
But the government stayed the course, arguing that it would be unwise to veer off into the unknown in the middle of a pandemic. Although the clinical trials did show some early protection from the first dose, no one knew how well that partial protection would last.
“When you’re talking about doing something that may have real harm, you need empirical data to back that,” said Dr. Céline R. Gounder, an infectious-disease specialist at Bellevue Hospital Center and a member of Mr. Biden’s coronavirus advisory board. “I don’t think you can logic your way out of this.”
But in recent weeks, proponents of delaying doses have been able to point to mounting evidence suggesting that a first dose can provide potent protection that lasts for a number of weeks.
The Centers for Disease Control and Prevention reported that two weeks after a single dose of either the Moderna or the Pfizer-BioNTech vaccine, a person’s risk of coronavirus infection dropped by 80 percent. And researchers in Britain have found that first-dose protection is persistent for at least 12 weeks.
Dr. Emanuel argued that Britain’s campaign to get first doses into more people had played a role in the 95 percent drop in cases since their peak in January. “It’s been pretty stunning,” Dr. Emanuel said.