Treating Ebola victims with blood plasma donated by Ebola survivors failed to significantly increase the odds of recovering from the deadly virus, according to a field test of the experimental treatment.
The conclusion is based on the cases of 84 people treated with plasma in Conakry, Guinea, in the hope that the antibodies in the fluid would help patients fight off the virus the way they did in the surviving donors.
The death rate was 31 percent with the plasma, compared to 38 percent in a control group of 418 sufferers treated at the same medical centre who did not receive survivor plasma, according to the results in the New England Journal of Medicine.
When the researchers adjusted for other factors that can affect survival, such as the age of the victims, the effect of plasma therapy was even less impressive.
"Of course you would like to dream and see a very strong reduction in mortality, but we didn't see this," chief author Dr Johan van Griensven of the Institute of Tropical Medicine in Antwerp, Belgium, told Reuters Health.
A key limitation of that study is that it's not known how many virus-fighting antibodies were in the plasma of the donors. Because Ebola virus disease, or EVD, is so dangerous, that analysis needs to be done in laboratories with special safety equipment, which are not available in affected countries, the researchers write.
"We might have anticipated there would be an effect" with plasma from survivors, said Dr William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center in Nashville, who was not connected with the research.
The fact that no benefit was seen "does not mean antibodies to Ebola are not going to be a good treatment," he cautioned. The plasma donors might not have been fully recovered, he noted, so the fluid might not have been rich in antibodies.
There were hints that some groups did benefit, though.
Children younger than five years old, known to have a poor prognosis, had the highest risk of death in the control group, but four of the five patients in this age group treated with convalescent plasma survived, van Griensven and his colleagues write. Although pregnant women with EVD also have a poor prognosis, six of the eight pregnant women treated with convalescent plasma survived, they added.
In another Ebola study, published as a letter to the Journal, researchers with the World Health Organisation report that men treated in Guinea, Liberia and Sierra Leone had a lower survival rate than women.
The disease killed 67.1 percent of the infected men versus 63 percent of the women.
The difference persisted even after adjusting for age, symptoms, and the amount of time it took for the person to seek medical help after falling ill, said co-author Dr Christl Donnelly of Imperial College London.
As of December 27, according to the WHO, 28,637 people have been infected with Ebola in the recent outbreak; 11,315 of those died. The most recent epidemic began two years ago in Guinea. On December 29, WHO declared the country to be free of the disease. If no new cases emerge by January 14, the epidemic will be considered over.
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