New research has found that infection and exposure to the 1918 influenza virus made survivors immune to the disease for the remainder of their lives.
The study, published in the journal Nature, found that antibodies produced by cells isolated from survivors served as an effective therapy to protect mice from the lethal 1918 infection.
An estimated 50 million people were killed by the 1918 flu pandemic worldwide.
"Our findings show that survivors of the pandemic have highly effective, virus-neutralising antibodies to this powerful virus,” said Dr Tshidi Tsibane, of the Mount Sinai School of Medicine, which contributed to the research findings.
"These findings could serve as potential therapy for another 1918-like virus," he added.