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Dr Anthony S. Fauci, the country’s top infectious disease specialist, told CNN on Friday that the United States will not follow Britain’s lead in the first front-loading vaccine injections, potentially delaying administration of the second doses.
Britain announced a plan this week to delay the second injection of its two licensed vaccines, developed by Pfizer and AstraZeneca, with the aim of delivering the partial protection conferred by a single dose to more people.
“I wouldn’t be in favor of that,” Dr. Fauci told CNN’s Elizabeth Cohen. “We will continue to do what we are doing.”
His opinion was endorsed by some experts, including Dr Eric Topol, a clinical trial expert at the Scripps Research Translational Institute in California, who tweeted, “That’s good because it tracks what we know, test data with an extraordinary 95% efficiency, avoiding extrapolation and unknowns.”
While clinical trials have tested the effectiveness of second doses given three or four weeks after the first, UK officials said they would allow an interval of up to 12 weeks. These delays have not been rigorously tested in trials. The Pfizer-BioNTech vaccine, for example, has been shown to be 95% effective in preventing Covid-19 when given in two doses, three weeks apart.
Stepping away from that diet, “it’s like going to the Wild West,” said Dr. Phyllis Tien, an infectious disease physician at the University of California, San Francisco. “It has to be data driven if they want to make a change.”
Widening the gap between vaccine doses could risk mitigating the benefits of the second shot, which aims to strengthen the body’s defenses against the coronavirus, increasing the strength and durability of the immune response. In the meantime, the protective effects on the first try may also wane more quickly than expected.
“We don’t really know what happens when you only take one dose after, say, a month,” said Natalie Dean, a biostatistician at the University of Florida. “It’s just not the way it’s been tested.”
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