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.
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.
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.“It’s a very dangerous proposal to leave the second dose to a later date,” said Dr.
In the clinical trial for the Pfizer-BioNTech vaccines, for example, volunteers enjoyed robust protection from Covid-19 two weeks after the second dose.
Once the British government authorized two vaccines — from Pfizer-BioNTech and AstraZeneca — it decided to fight the variant by delaying the second doses of both formulations by 12 weeks.
By contrast, the United States has delivered at least one dose to just 33 percent of Americans.
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.The Centers for Disease Control and Prevention reported that two weeks after a single dose of either the Moderna or the Pfizer-BioNTech vaccine, a person’s risk of coronavirus infection dropped by 80 percent.
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 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.She and others are also worried by recent studies that show that a single dose of Moderna or Pfizer-BioNTech does not work as well against certain variants, such as B.1.351, which was first found in South Africa.
Getting more people vaccinated — even with moderately less protection — could translate into a bigger brake on the spread of the virus in a community than if fewer people had stronger protection, they 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.
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