Doctors have sometimes used blood from Ebola survivors to treat others afflicted with the virus, but a study suggests the strategy has little effect.

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 New England Journal of Medicine Thursday.

"We would have liked to have seen more dramatic results," said Johan van Griensven of the study in Guinea, the paper's lead author. "But this doesn't mean (blood) plasma treatment doesn't work by definition."

He said antibody levels are often low in patients who have only recently recovered from Ebola and that doctors might need to use blood from long-term survivors to get a better effect.

Some said the disappointing results should be enough to convince scientists to abandon this strategy.

"From the data presented, it doesn't look like this is worth pursuing," said Thomas Geisbert, an Ebola expert at the University of Texas Medical Branch at Galveston. He was not connected to the latest research.

"The idea that antibodies from a person who survived Ebola could save lives was always a long shot, but it was too good an idea not to test," said Ben Neuman, a virologist at Britain's University of Reading.