
A trial investigating the drug hydroxychloroquine as a preventative treatment against Covid-19 may never find out if it's effective, say scientists involved.
Controversy around the drug - touted by President Trump and the subject of online misinformation - is stopping completion of the trial, they say.
It is ineffective in hospitalised patients, but investigators hope it might work if given earlier on.
Hospitals have pulled out of the trial.
The Oxford University-led trial is aiming to enrol 40,000 frontline workers around the world.
Investigators hope the large-scale, double-blind randomised study will show if early use of the treatment prevents the virus from getting worse.