Researchers in the US are conducting a clinical trial of a treatment for COVID-19, the illness caused by the new coronavirus, the National Institutes of Health announced yesterday. There are currently over 80,000 confirmed cases of the disease around the world, and it has killed 2,770 people.

Two trials of the drug, an experimental antiviral called remdesivir, have already been up and running in China for a few weeks — and preliminary results appear promising. “There is only one drug right now that we think may have real efficacy and that’s remdesivir,” said Bruce Aylward, an assistant director-general of the World Health Organization (WHO), at a press conference this week.

In lab experiments, remdesivir blocks the activity of the new coronavirus in cells. It’s also effective against MERS and SARS, which are also coronaviruses, in cells. It hasn’t yet been tested against those particular diseases in humans. It was first developed by the pharmaceutical company Gilead to treat Ebola. A handful of COVID-19 patients, including the first US patient, have been given the drug under compassionate use, which allows doctors to give experimental drugs to patients when no other options are available. The treatment appeared to help in some of those cases, but it takes a clinical trial, like the ones that are underway, for experts to conclusively know if it works.

The first site for the US trial is at the University of Nebraska Medical Center. The first patient enrolled was passenger repatriated to the US after being on the Diamond Princess cruise ship, which was quarantined off the coast of Japan and had an outbreak of the virus on board. The trial aims to run at a number of sites around the world, in order to allow people in the largest geographic area possible to participate, says lead investigator Andre Kalil, a professor of internal medicine at the University of Nebraska Medical Center. The goal is to enroll around 400 people with COVID-19.

Only patients experiencing severe symptoms are eligible for the trial. “About 80 percent of people have mild disease. They will clear the infection on their own,” Kalil says. “The goal here is to help the ones that are in the most need, who acquired the virus and need to be in a hospital.”

Participants will be randomly assigned to either receive the drug or a placebo. The study was designed to be flexible, though, and if it starts to show that the drug works, the patients in the placebo group will also receive it. The most important thing the study will measure, Kalil says, is if patients start to get better. It’s much more geared toward finding clinical improvement than toward finding a specific dose or understanding the way the drug works.

The trial was put together in a matter of weeks. “It’s amazing how fast this happened,” Kalil says. “This is landmark, that it could be done this fast.”

Results from the remdesivir trials in China may be available as soon as April. The US-run trial is scheduled to run through 2023, but there may be preliminary data within the year. Research teams and pharmaceutical companies are also working to develop vaccines for the new coronavirus, but that process will take much longer — a year to 18 months at the fastest, experts say.

The remdesivir trials are just a few of the dozens of ongoing clinical trials testing treatments for COVID-19, targeting tens of thousands of patients. The scale and speed are remarkable — even more so given that, only a few years ago, the public health community was reluctant to use experimental treatments during active outbreaks.

Like with the new coronavirus, there were no proven treatments available for Ebola in 2014 when an epidemic broke out in West Africa. At the start, the WHO was concerned that experimental products would increase the already-high levels of mistrust in health workers, and experts worried that focusing on research studies would take resources away from providing active care to sick patients.

But the WHO quickly outlined recommendations for conducting research during the crisis, and trials on various treatment options started up. Scientists learned useful ways to structure trials and thought through some of the ethical issues involved.

Those approaches were refined in the still-ongoing epidemic of Ebola in Congo, which started in 2018. A study of four different drugs found that two were effective — and did so in the middle of the ongoing outbreak. “This is the first time that a randomized, controlled trial has shown quickly and successfully what the best drugs are in the middle of an ongoing outbreak,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which is part of the National Institutes of Health, told The Verge at the time.

Researchers will hope to repeat that success now. The setup of the study for the US remdesivir trial is based on the design of the four-drug Ebola trial, Kalil says. The ongoing outbreak of the new coronavirus is different from the Ebola epidemics because it’s less deadly, but it’s affecting far more people in many more countries around the world. But the ongoing response benefits from those experiences, as will the response to any future public health crises. “We are learning,” he says. “What we learned from Ebola is definitely something that is helping us to be even better during this outbreak.”

Update February 26, 4:51PM ET: Updated with comments from Andre Kalil.