Dr. Anthony S. Fauci, the nation’s top infectious disease expert, told CNN on Friday that the United States would not follow Britain’s lead in front-loading first vaccine injections, potentially delaying the administration of second doses.
Britain announced a plan this week to delay second shots of its two authorized vaccines, developed by Pfizer and AstraZeneca, in an attempt to dole out to more people the partial protection conferred by a single dose.
“I would not be in favor of that,” Dr. Fauci told CNN’s Elizabeth Cohen. “We’re going to keep doing what we’re doing.”
His opinion was met with approval by some experts, including Dr. Eric Topol, a clinical trials expert at the Scripps Research Translational Institute in California, who tweeted, “That’s good because that it’s following what we know, the trial data with extraordinary 95 percent efficacy, avoiding extrapolation and the unknowns.”
While clinical trials tested the efficacy of second doses delivered three or four weeks after the first, British officials said they would allow a gap of up to 12 weeks. Such delays have not been rigorously tested in trials. The Pfizer-BioNTech vaccine, for instance, was shown to be 95 percent effective at preventing Covid-19 when administered as two doses, three weeks apart.
Straying from this regimen “is like going into the Wild West,” said Dr. Phyllis Tien, an infectious disease physician at the University of California, San Francisco. “It needs to be data driven if they’re going to make a change.”
Widening the gap between vaccine doses could risk blunting the benefits of the second shot, which is intended to boost the body’s defenses against the coronavirus, increasing the strength and durability of the immune response. In the interim, the protective effects of the first shot could also wane faster than anticipated.
“We don’t really know what happens when you only have one dose after, like, a month,” said Natalie Dean, a biostatistician at the University of Florida. “It’s just not the way it was tested.”
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