Study hints, can't prove, survivor plasma fights COVID-19

Mayo Clinic researchers reported a strong hint blood plasma from Covid-19 survivors helps other patients recover, but it's not proof and some experts worry if, amid clamor for the treatment, they'll ever get a clear answer.

More than 64,000 patients in the US have been given convalescent plasma, a century-old approach to fend off flu and measles before vaccines. It's used when new diseases emerge and history suggests it works against some but not all infections.