Stretching the time between the first and second doses would greatly accelerate the rate at which people get at least partial protection. But some experts fear it could also lead to new variants.
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.
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.
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 inside the bodies of partially vaccinated people who are not able to swiftly fight off an infection.
“It’s a very dangerous proposal to leave the second dose to a later date,” said Dr. Luciana Borio, the former acting chief scientist of the Food and Drug Administration. Dr. Anthony S. Fauci, the nation’s top infectious-disease expert, agreed. “Let’s go with what we know is the optimal degree of protection,” he said.
In January, some researchers lobbied for the United States to follow Britain’s example.
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.
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.
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.
He points to data like this as further evidence that the United States should stretch out vaccinations. He and his colleagues estimate that if the country had used a 12-week schedule from the start of its rollout, an additional 47 million people would have gotten at least one dose by April 5.
Sarah E. Cobey, an epidemiologist and evolutionary biologist at the University of Chicago, said she thought that the United States had lost a precious opportunity to save many lives with such a strategy. “We’ve missed a window, and people have died,” she said.
But even now, Dr. Emanuel said, it’s worth delaying doses. The United States is giving out roughly three million vaccines a day, but nearly half are going to people who have already received one shot. The nation’s entire supply, he argued, should instead be going instead to first-timers.
If that happened, it would take two or three weeks for the United States to catch up with Britain, according to his team’s calculations. The extra protection would not just save the lives of the vaccinated but would help reduce transmission of the virus to people yet to get any protection.
Still, some scientists say it’s premature to credit the delayed vaccination schedule for Britain’s drop in cases.
“They’ve done a few other things, like shut down,” Dr. Fauci said.
“I think the real test will be whether we see a rebound in cases now that the U.K. is reopening.” Dr. Gounder said.
Instead of experimenting with vaccination schedules, critics say it would be wiser to get serious about basic preventive measures like wearing masks. “It’s crucial that we don’t just reopen into a big national party,” Dr. Borio said.
“Relying on one dose of Moderna or Pfizer to stop variants like B.1.351 is like using a BB gun to stop a charging rhino,” said John P. Moore, a virologist at Weill Cornell Medicine.
Dr. Moore said he also worried that delaying doses could promote the spread of new variants that can better resist vaccines. As coronaviruses replicate inside the bodies of some vaccinated people, they may acquire mutations that allow them to evade the antibodies generated by the vaccine.
But Dr. Cobey, who studies the evolution of viruses, said she wasn’t worried about delayed doses breeding more variants. “I would put my money on it having the opposite effect,” she said.
“There are fewer infected people in which variants can arise,” she said.
Dr. Adam S. Lauring, a virologist at the University of Michigan who was not involved in the commentary, said he felt that Dr. Cobey and her colleagues had made a compelling case. “The arguments in that piece really resonate with me,” he said.
Although it seems unlikely that the United States will shift course, its neighbor to the north has embraced a delayed strategy to cope with a booming pandemic and a short supply of vaccines.
Dr. Catherine Hankins, a public health specialist at McGill University in Montreal and a member of Canada’s Covid-19 Immunity Task Force, endorsed that decision, based on the emerging evidence about single doses. And she said she thought that other countries facing even worse shortfalls should consider it as well.
“I will be advocating at the global level that countries take a close look at Canada’s strategy and think seriously about it,” Dr. Haskins said.
Source: New York Times