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In the Moderna and Pfizer trials, a small number of volunteers received just one dose. In the Pfizer trial, there was 52 per cent efficacy in the first three weeks after the first dose; the Moderna trial found roughly 80 per cent efficacy at four weeks.
But the second dose provides a dramatic boost in the immune response — “much closer, or arguably even better than that found with natural infection,” said Dr. Paul Offit, a professor of paediatrics at Children’s Hospital of Philadelphia and member of the U.S. Food and Drug Administration’s advisory committee evaluating COVID-19 vaccines. “Nobody disagrees that you need a second dose,” he said. The second dose induces more robust T-cell immunity, memory cells that provide longer-lasting immunity. “So why delay it?”
It’s not known, from the original trials, how long the first dose would be effective, beyond those first few weeks, he said. “And when you disrupt the program by saying, ‘look, we’ll give you the second dose when we can,’ a lot of people aren’t going to get the second dose.
“More importantly, a lot of people, having gotten only one dose, will think that they’re at some level protected when they may not be protected at all after two or three or four months. It’s a terrible idea.”
The vaccines also shouldn’t be mixed, even in a pinch, he said. “They’re two different molecules, they’re constructed differently. Again, there’s no data.”
We have vaccines, remarkably, within one year of identifying and sequencing this virus that induce up to 95 per cent efficacy, including against severe disease and in people older than 65, Offit said. “Our job now is to mass produce them and figure out a way to distribute and administer them. That should be the effort. That should be the discussion.”
The public’s confidence is a fragile confidence, Offit said. Fiddling with authorized dosing schedules “goes away from the science.
“It makes us look like we don’t know what we’re doing.”