Due to the increasing coronavirus cases, emergence of more transmissible variants, and slow vaccine rollout, some countries have decided to delay the rollout of the second coronavirus shot to make sure everyone gets at least a shot.
This has sparked debates among scientists, some of which fear that delaying the second coronavirus shot can lead to a more transmissible variant of the virus.
The UK and the US take different approaches to deliver the second vaccine shot
In the United Kingdom, where researchers have raised concerns about a new coronavirus variant that appears to be more contagious than other versions, officials are choosing to extend the time between each vaccine dose from three or four weeks to up to three months.
The United States, on the other hand, are sticking to the regimen recommended by the US Food and Drug Administration authorized in December—two shots spaced three weeks apart for Pfizer-BioNTech’s vaccine, and four weeks apart for Moderna’s.
Delaying the second shot might leave millions of people unprotected
Experts are concerned about the delay in administering the vaccine because it might lead to millions of people walking around with only partial immunity to the coronavirus, a condition that could be ripe for harmful mutations of the virus to arise.
“Delaying the second shot is a gamble,” says Ramón Lorenzo-Redondo, a virologist at Northwestern University Feinberg School of Medicine in Chicago, “particularly without a lot of evidence suggesting how well one dose works. Officials shouldn’t gamble [their] best tools to fight the pandemic,”
“We don’t want to fuel [potential viral evolution] by doing suboptimal immunization of the population.” He says.
Sarah Cobey, an epidemiologist and evolutionary biologist at the University of Chicago, is one of the scientists who aren’t worried about the risk of a long delay between shots.
“That’s because even the partial protection that people may get from a single dose will almost certainly lower the prevalence of infection,” she says.
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