Giving the blood of Ebola survivors to patients didn't seem to make a difference, doctors found in the biggest study so far on the approach, prompting some scientists to say it's time to abandon the strategy.

With no licensed treatment for the devastating disease, doctors have sometimes used blood from survivors to treat the sick, hoping its infection-fighting antibodies might help patients defeat the virus. It seemed to help some patients in the past but there was no clear proof. Amid the world's biggest outbreak of Ebola in West Africa in 2014, scientists decided to put the treatment to the test in Guinea.

At a clinic in the capital Conakry, scientists found no difference in survival between 84 patients who got survivor blood compared to about 400 patients treated some five months earlier, according to the study published in the New England Journal of Medicine on Thursday.