In October 1918, Lieutenant L.W. McGuire of the United States Navy sent a report to the American Journal of Public Health detailing a promising therapy that had already saved the lives of a number of officers suffering from pneumonia complications due to the Spanish influenza outbreak.

McGuire described how transfusions of blood from recovered patients – an idea which had first been trialed during a polio epidemic in 1916 – had led to rapid recovery in a series of severe pneumonia cases at a Naval Hospital in Massachusetts. “It is believed the serum has a decided influence in shortening the course of the disease, and lowering the mortality,” he wrote.

Now more than a century on, this treatment – long forgotten in the western world – is once again coming to the fore during the current COVID-19 pandemic. With fatalities continuing to rise, and no vaccine expected for many months, experts are urging medical centers across the U.S. and Europe to initiate collaborations between critical care and transfusion services to offer this as an emergency treatment for those who need it most.

As of March 20, there are more than 90,000 individuals globally who have recovered from the disease. Some scientists believe that the blood of many of these people contains high levels of neutralizing antibodies that can kill the virus.

“These antibodies then become essentially drugs,” said Arturo Casadevall, professor of Molecular Microbiology & Immunology at John Hopkins Bloomberg School of Public Health, who is currently co-ordinating a clinical trial of convalescent serum for COVID-19 involving 20 institutions across the US.

“We’re talking about preparing a therapy right out of the serum of those that have recovered. It could also be used in patients who are already sick, but have not progressed to respiratory failure, to treat them before they enter intensive care units. That will provide a lot of support because there’s a limited number of respirators and resources.”

The first conclusive data on how the blood of recovered patients can help tackle COVID-19 is set to come out of China, where it was also used as an emergency treatment during the SARS and MERS outbreaks. On February 9, a severely ill patient in Wuhan was treated with convalescent serum and since then, hospitals across China have used the therapy on a total of 245 patients, with 91 reportedly showing an improvement in symptoms.

In China alone, more than 58,000 patients have now recovered from COVID-19. Casadevall said that last week the country shipped 90 tons of serum and plasma from these patients to Italy – the center of the pandemic in Europe – for emergency use.