Survivors of COVID-19 are donating their blood plasma in droves in hopes it helps other patients recover from the coronavirus. And while the jury's still out, now scientists are testing if the donations might also prevent infection in the first place.

Thousands of coronavirus patients in hospitals around the world have been treated with so-called convalescent plasma - including more than 20,000 in the US - with little solid evidence so far that it makes a difference. One recent study from China was unclear while another from New York offered a hint of benefit.

"We have glimmers of hope," said Dr. Shmuel Shoham of Johns Hopkins University.

With more rigorous testing of plasma treatment underway, Shoham is launching a nationwide study asking the next logical question: Could giving survivors plasma right after a high-risk exposure to the virus stave off illness?

To tell, researchers at Hopkins and 15 other sites will recruit health workers, spouses of the sick and residents of nursing homes where someone just fell ill and "they're trying to nip it in the bud," Shoham said.

It's a strict study: The 150 volunteers will be randomly assigned to get either plasma from COVID-19 survivors that contains coronavirus-fighting antibodies or regular plasma, like is used daily in hospitals, that was frozen prior to the pandemic. Scientists will track if there's a difference in who gets sick.

It if works, survivor plasma could have important ramifications until a vaccine arrives - raising the prospect of possibly protecting high-risk people with temporary immune-boosting infusions every so often.

"They're a paramedic, they're a police officer, they're a poultry industry worker, they're a submarine naval officer," Shoham ticked off. "Can we blanket protect them?"

The new coronavirus has infected more than 7 million people worldwide and killed more than 400,000, according to official tallies believed to be an underestimate. With no good treatments yet, researchers are frantically studying everything from drugs that tackle other viruses to survivor plasma - a century- old remedy used to fight infection before modern medicines came along.