Of the 107 people who fell ill, 49 were in the hydroxychloroquine group and 56 were in the placebo group - a 2.4% difference.
The study whipped up fresh controversy over hydroxychloroquine, which has been endorsed by public figures - including US President Donald Trump - despite concerns over side effects and a lack of evidence that it is effective.
Researchers looked at 821 people who were exposed to the virus either through their line of worker as a healthcare professional, or from someone at home.
It found 11.8% of subjects given hydroxychloroquine developed symptoms compatible with COVID-19, compared with 14.3%who got a placebo.
The key finding is that hydroxychloroquine, the most common preparation of drugs typically used to prevent malaria and to help those with autoimmune conditions such as lupus and rheumatoid arthritis, "was not able to prevent the development of COVID-19 any better than a placebo".
"On the basis of the available mortality data. the executive group will communicate with the principal investigators in the trial about resuming the hydroxychloroquine arm", Ghebreyesus said in a virtual news briefing.
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After suspending the hydroxychloroquine arm of a clinical trial of experimental COVID-19 drugs, the director-general of the World Health Organisation said experts had reviewed the safety data and were now recommending the trial continue as planned.
The Lancet medical journal said on Tuesday "serious scientific questions" had been brought to its attention about the validity of the data behind a widely cited and already corrected study on the dangers of the use of the anti-malarial drug hydroxychloroquine in hospitalized patients with COVID-19.
Trump took a two-week course of hydroxychloroquine, along with zinc and Vitamin D, after two staffers tested positive for COVID-19, and had no ill effects, according to results of his latest physical released by his doctor Wednesday.
"I think in the setting of post-exposure prophylaxis, it doesn't seem to work", said Sarah Lofgren, an assistant professor at the University of Minnesota who is a co-author of the study.
As of Wednesday, Bangladesh had confirmed 55,140 coronavirus cases with the death toll rising to 746 after 37 new fatalities were reported. He later said he took the drugs preventively after two people who worked at the White House were diagnosed with COVID-19, the illness caused by the novel coronavirus. It does not prevent infection, ' Boulware said.
Mandeep Mehra, a physician at Brigham and Women's hospital and lead author of the study, in a statement said The Lancet this week informed the authors of a discrepancy in the Australian hospital data, leading the authors to discover that data from a hospital in Asia had been incorrectly incorporated into the data from hospitals in Australia, but that the error did not affect the study's conclusions. "And this study stopped or paused a couple of those trials, and changed the narrative around a drug that no one knows if it works or not", he said.