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MONDAY, Jan. 4, 2021 (HealthDay News) -- If a second dose of the first COVID-19 vaccine isn't available or the maker isn't known, then another vaccine may be used, new British guidelines say, The New York Times reported Sunday.
The new guidance contradicts those in the United States, where the U.S. Centers for Disease Control and Prevention has said that Covid-19 vaccines "are not interchangeable," and that "the safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product."
Some experts say the British policy is gambling. "There are no data on this idea whatsoever," John Moore, at Cornell University, told the Times. Britain officials "seem to have abandoned science completely now and are just trying to guess their way out of a mess," he said.
Britain has green-lighted vaccines from Pfizer and AstraZeneca. According to the new guideline, "every effort should be made" to use the same vaccine for the second dose. But if "the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product" for the second shot.
"This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again," the guidelines say. Because both vaccines attack the virus in the same way, "it is likely the second dose will help to boost the response to the first dose."
But there's no proof that the vaccines are interchangeable.
"None of this is being data-driven right now," Dr. Phyllis Tien, an infectious disease expert at the University of California, San Francisco, told the Times. "We're kind of in this Wild West."
Both vaccines teach immune cells to recognize and fight off the virus. But they use different methods and contain different ingredients.
With no evidence to back it, this approach seems "premature," Saad Omer, a vaccine expert at Yale University, told the Times.
The newspaper also reported that second doses may be delayed as the country tries to vaccinate more of its citizens more quickly.
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