Handicapping the results of the severe Covid-19 study requires some deep-in-the-weeds modeling of biostatistics. Thankfully, Umer Raffat, a biotech analyst at Evercore ISI, has done the heavy lifting for his investor clients.

If people who take the placebo show clinical improvement after 16 days, remdesivir would have to track at 13 days to demonstrate superiority with statistical significance, Raffat said. This would be described in what researchers call a “hazard ratio.” The magic number would be 1.2, meaning that patients do 20% better on remdesivir than placebo.

There is already one red flag. The investigators running the severe Covid-19 study in China have already taken an interim look at the data, but they did not stop the study early. This suggests remdesivir isn’t working as well as hoped, and dampens optimism for an overall positive outcome, Raffat said.

It’s also possible the trial will produce mixed results.