What is COVID-19 human challenge testing? Doctors explain how it works

SAN FRANCISCO (KGO) -- With the world racing to develop a vaccine for COVID-19, there's an ethical debate about a strategy that could potentially speed up the testing.

That strategy is a form of clinical trial that involves deliberately exposing volunteers to the virus.

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Right now, roughly half a dozen government-backed COVID-19 vaccine candidates are lined up in traditional clinical trials across the U.S.

Thousands of volunteers will ultimately receive doses of a specific candidate, then return to their normal lives where researchers will follow them for signs of infection or immunity. But what if researchers didn't have to wait for those volunteers to come in contact with the virus naturally, and instead, exposed them to it deliberately? A technique known as a "human challenge trial."

"These things are not done very often, they're certainly not done in the modern era. They were done in years past," says Dr. Yvonne Maldonado, M.D., an infectious disease specialist at Stanford Health Care.

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Dr. Maldonado points to smallpox as an early example. An English doctor successfully tested his own rudimentary vaccine on an eight-year-old boy. Before modern clinical trials evolved, human challenge trials offered a relatively simple and fast way to get data back on a vaccine, but with dangers included.

"Of course the risk of a healthy young person is not zero no matter what. So you could still risk somebody getting very sick," says Dr. Maldonado.

With a disease there is still no approved treatment for.

But on Friday, Dr. Anthony Fauci confirmed to several media sources that the U.S. is now working on a weakened version of the COVID virus, which would be needed for any human challenge trial. Dr. Fauci said the move was only precautionary and that no trials are currently planned.

Still, at a recent web briefing by UCSF, Dr. Joel Ernst, M.D. said leaders in the medical community have been actively debating the pros and cons.

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"So there are disagreements about how much risk volunteers or participants would be subjected to," explained Dr. Ernst.

At least one vaccine group at Oxford has already requested permission from the U.K. to conduct a challenge trial if the numbers of available volunteers were to drop. Some advocates argue that tests with a weakened virus could be conducted quickly and safely. Still, with millions of doses required world-wide, the stakes may be historically high.

"If we don't produce a safe vaccine we will lose the confidence of the public immediately, and it's really hard to regain that," Dr. Maldonado points out.

With the no shortage of COVID-19 patients at this point, Dr. Fauci said he still believes the current trial structure will prove the quickest path to a safe vaccine.

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