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WASHINGTON (AP) — President Donald Trump on Thursday visited the headquarters of the American Red Cross to encourage survivors of COVID-19 to donate plasma. (Watch our previous report on the need for plasma donations in the video above.)

Thousands of coronavirus patients have donated their plasma in hopes it could help other patients recover from the coronavirus, and scientists are testing if the donations might also prevent infection in the first place. Medical experts say the jury is still out on effectiveness of convalescent plasma on both fronts.

Trump was joined by several members of his coronavirus task force for the visit to Red Cross, and even stopped to visit with a plasma donor. Health and Human Services Secretary Alex Azar said 50,000 donors have given plasma but the nation needs hundreds of thousands of more donors to come forward.

If 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.

Convalescent plasma’s most famous use was during the 1918 flu pandemic.

For much more on blood donation or to schedule an appointment, click here.