Researchers are launching a study to see whether blood plasma from coronavirus survivors can block infection in others.

The study will involve people in groups at high risk of getting infected. This could include health workers, husbands or wives of sick individuals and people who live in nursing homes.

The new research will build on recent studies that looked into whether blood plasma from recovered coronavirus patients could be an effective treatment for infected individuals.

Plasma is the yellowish, liquid part of blood. It contains proteins called antibodies that target infections entering the body. Blood plasma from former patients may help infected individuals defeat COVID-19, the disease caused by the coronavirus.

Many survivors of COVID-19 have donated their blood plasma in hopes of helping sick patients recover.

Thousands of coronavirus patients in hospitals around the world have been treated with this kind of plasma, including more than 20,000 in the United States.

So far, there is little evidence to demonstrate that blood plasma is helping coronavirus patients recover. One recent study from China had unclear results. Another from New York showed only small benefits.

Dr. Shmuel Shoham of America's Johns Hopkins University told The Associated Press that the studies do provide some "glimmers of hope." Shoham will lead the new study on whether the plasma can prevent infections entirely.

Researchers plan to use 150 volunteers for the study. Some of the test subjects will receive plasma from COVID-19 survivors that contains coronavirus-fighting antibodies. Others will receive a kind of plasma used daily in hospitals. Scientists will examine whether there are differences in who gets sick.

If the survivor plasma works, it could play a major part in reducing the number of coronavirus infections until a vaccine is approved. The researchers say the survivor plasma could be given to high-risk individuals to temporarily strengthen the immune system.

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

As more people survive COVID-19, there are increasing calls for them to donate plasma to build up the nation's supply, in case the treatments prove to be effective.

Donated blood plasma is also sometimes combined with products designed to make the plasma stronger. The Spanish chemical company Grifols is expected to create a version of donor plasma that is filled with a large amount of antibodies.

Using blood plasma directly from recovered patients seems to be safe, Dr. Michael Joyner of the Mayo Clinic reported last month. His team followed the first 5,000 people to receive plasma in a program run by the U.S. Food and Drug Administration.

The program, which helps hospitals carry out the experimental treatment, found few serious side effects in patients.

I'm Bryan Lynn.

The Associated Press reported this story. Bryan Lynn adapted the report for VOA Learning English. Ashley Thompson was the editor.