1 dose or 2? CDC vaccine study raises question about prioritizing single shots for more people

North Carolina

RALEIGH, N.C. (WNCN) — A new real-world CDC study found the two-dose COVID-19 vaccines to be highly effective after the first shot.

It raised a question: If one dose works so well outside of clinical trials, should national and state leaders change their priorities to getting more people that first dose and delaying those second shots?

Fortunately, with the vaccines not as scarce as they were weeks and months ago, it’s not as pressing an issue as it once could have been.

“The good news is, here in the United States, we can have our cake and eat it, too,” said Dr. David Wohl, an infectious disease specialist at the University of North Carolina School of Medicine. “We can get enough people vaccinated — fully, meaning first dose and second dose, if we’re talking about Pfizer or Moderna. So I don’t think we have to make that choice.”

But what if we did?

The study published earlier this week by the Centers for Disease Control and Prevention followed 3,950 healthcare workers, first responders and frontline workers across the country. 

It found a single dose of the vaccines was 80 percent effective at preventing infections of COVID-19, with the efficacy rate climbing to 90 percent two weeks after the final dose of the two-shot regimen.

Some health experts worry people might think a single dose is good enough, or that it might be better overall to focus on getting more single shots to more people as opposed to emphasizing those second doses.

“Under normal circumstances, the vaccines should be deployed in keeping with the trial protocols,” Dr. Robert Wachter of the University of California, San Francisco, wrote in the New England Journal of Medicine earlier this month. 

“However, the current circumstances — a slow vaccine rollout, a limited vaccine supply, and the recent emergence of more infectious SARS-CoV-2 variants that threaten to outpace our vaccination program — are anything but normal,” he wrote. “This may be a case in which the risks of strict adherence to the plan outweigh the risks of modifying it.”

But Wohl says changing course comes with a risk that has to do with timing. 

Because subjects in those studies were only followed for a few months — the recent CDC study lasted from mid-December to mid-March — it’s unknown if the vaccine’s effectiveness eventually will drop without that boost from the second dose.

“All these studies have only followed people for a pretty short period of time,” Wohl said. “And what we worry about with one dose is the durability of the protection. And so we don’t know how long that protection lasts after one dose versus the double whammy of two doses.”

An earlier study found the Pfizer vaccine had an efficacy of only 52 percent after one dose.

Wohl says the numbers behind this study are more reliable because its subjects took COVID-19 tests weekly.

“These were really smart studies. They tested people weekly for the presence of virus in their noses. That took forethought. That took planning,” Wohl said. “We just really have great opportunities to learn a lot about infection, because people plan studies like this where they said, ‘If you’re going to get the vaccine, that’s great, but why don’t we swab your noses once a week for the next several weeks?’ That’s how we got really good data.”

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