To speed vaccination, some call for delaying second shots

The prospect of a fourth wave of the coronavirus, with new cases climbing sharply in the Upper Midwest, has reig- nited 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, twodose 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 Health- care 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. Emanuel and his colleagues published the proposal in an op-ed on Thursday in USA Today.

But opponents, including health advisers to the Biden administration, argue that delaying doses is a bad idea. They warn it will leave the country vulnerable to variants — those already circulating, as well as new ones that could evolve among partially vaccinated people.