Adding to the challenges, advocates and experts say, most low-income countries lack adequate testing and diagnostic tools to identify patients early enough for the treatments to help.

“There’s lots of logistics and training and community health literacy that has to happen in order for this to work well,” Brook Baker, professor at Northeastern University School of Law who works with the Access to Covid-19 Tools Accelerator, a World Health Organization-backed effort meant to ease access to Covid-19 vaccines, treatments and diagnostics.

Studies have found subjects needed to begin taking the pills within five or fewer days of developing symptoms, making it critical for doctors to quickly identify patients who will benefit.

Most people in poor countries have little-to-no access to Covid-19 testing and often get access only when they are already hospitalized.