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Public health officials say it's important to vaccinate as many people as quickly as possible to reduce the risk posed by new coronavirus variants. One strategy to stretch existing supplies – albeit with huge logistical challenges — would be to give just one dose of the vaccine to people who have recovered from COVID-19.

About half a dozen small studies, all consistent with one another but as yet unpublished, suggest this strategy could work.

Dr. Mohammad Sajadi, at the University of Maryland medical school's Institute of Human Virology 

 who were just getting their first of two vaccine shots. His research team homed in on those who had previously been diagnosed with COVID-19.

"We saw a much faster response and a much higher response," he says, based on the protective antibodies his team measured in the blood. The infection served the same priming role as an initial dose of the Moderna or Pfizer vaccine would have, so the first shot they got was in effect a booster. It amplified and solidified immunity to COVID-19. 

the journal of the American Medical Association. 

The Johnson & Johnson vaccine authorized Saturday by the Food and Drug Administration only requires a single dose.

So, he says while vaccine is scarce, it makes sense to offer just one shot to people who have already had the disease.

"You can free up automatically millions of doses," he says, increasing vaccine supply by 4 percent or 5 percent. "We think it makes sense at this time to promote such a policy."

Federal health officials are intrigued. Dr. Anthony Fauci, who serves as COVID-19 adviser to the White House, has said it's an idea worth further study. He is dead set against another strategy, which is stretching out the time between first and second doses. 

But health officials are not ready to say yes. For one thing, there are still lots of questions, says 

, an epidemiologist at the University of North Carolina's Gillings School of Global Public Health.

For one: "Does the vaccination response last as long as it would for somebody who had two vaccines?" she asks. That's not known. Also, the blood tests that measure vaccine effectiveness may not fully indicate whether a person is immune or not.

 looking at this issue, and it too found that a single dose stimulated strong immune reactions in 10 people who had recovered from COVID-19. Her study also bears on a practical question, which is how to identify the people who have previously been sick. 

One idea is to test for coronavirus antibodies in the blood. But she says those can fade unpredictably, "so using antibody levels would not be a foolproof way of identifying individuals who have had past infection."

And testing for antibodies would add another layer of complexity to a system that's complicated enough as it is. 

So, a better strategy might be to focus on the people who have had a 

"The trick will be in narrowing in on those 28 million people who have tested positive, communicating with them, and then getting them vaccinated," says 

, senior director of clinical guidelines and quality improvement at the American Society of Health-System Pharmacists.

One question is where to find information about those diagnoses. It's scattered inconveniently in individual medical records, but it has also been collected by state and local health departments, who used it for contact tracing.

"I guess I would see the data coming from more the state level, where it's linking the immunization registries with the state departments of health," she says.

, a law professor at Georgetown University. He says that state data are only supposed to be used for public health purposes, and sharing them with, say, a pharmacy that as a vaccine sign-up system is "really stretching the lawfulness and ethics for what you could do." Patients might individually have to give consent to release their data, he says.

What's more, these databases aren't currently configured for that purpose, and it could take many months to do that, by which time vaccines may no longer be in short supply.

"I know it is a little bit wishful thinking," says Legreid Dopp. She's frustrated that there is so much health data out there that could be linked and organized, but systems to do that are often cumbersome or nonexistent.

This strategy could make sense in countries like England and Israel, which have strong centralized health systems. But the U.S. system just isn't set up that way.  "This is American exceptionalism, and not in a good way," Gostin says.

And adding these complexities could well bog down the struggling vaccination system bog down rather than speed it up.

"With three completely different vaccines going as early as next week, I think that state and local health departments are going to be really taxed on logistics," Claire Hannan, executive director of 

, told NPR in an email. "We need to do everything we can to simplify things."

You can contact NPR Science Correspondent Richard Harris at 

Richard Harris

Author

People who have been sick with COVID-19 may need only one dose of the normally two-shot vaccines. If that became policy it could extend vaccine supplies, but logistical challenges are daunting.

Could a single-dose of COVID-19 vaccine after illness stretch the supply?

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