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.
There's no solid evidence yet that it fights the coronavirus and, if so, how best to use it. But preliminary data from 35,000 coronavirus patients treated with plasma offers what Mayo lead researcher Dr Michael Joyner on Friday called "signals of efficacy."
There were fewer deaths among people given plasma within three days of diagnosis and also among those given plasma containing the highest levels of virus-fighting antibodies, Joyner and colleagues reported.
However, this wasn't a formal study. Patients were treated in different ways in hospitals as part of a Food and Drug Administration programme designed to speed access to the experimental therapy.
That so-called "expanded access" programme tracks what happens to recipients, but can't prove the plasma — and not other care they received — was the real reason for improvement.
Rigorous studies underway around the country are designed to get that proof, by comparing similar patients randomly assigned to get plasma or a dummy infusion in addition to regular care. But those studies have been difficult to finish as the virus waxes and wanes in different cities. Also, some patients have requested plasma rather than agreeing to a study that might give them a placebo instead.
"For 102 years we've been debating whether or not convalescent plasma works," said Dr Mila Ortigoza of New York University, referring to plasma's use in the 1918 flu pandemic. This time around, "we really need undisputed evidence."
Ortigoza is co-leading such study, which this week is expanding to three other states — Connecticut, Florida and Texas. Her team is working to pool data with several other clinical trials with hopes of faster answers.
"There's concern about when there will be a clear answer," agreed infectious disease specialist Dr Jeffrey Henderson of Washington University in St Louis.