Gilead's remdesivir helps another set of hospitalized COVID-19 patients. But just how much?

Gilead Sciences has more data to show its antiviral remdesivir can help COVID-19 patients, even those with moderate disease.

According to Gilead’s own phase 3 Simple trial, adding remdesivir to standard of care for just five days of treatment was 65% more likely to improve the clinical symptoms of moderate COVID-19 pneumonia versus standard of care alone, the company said Monday.

But don’t confuse symptom improvement with full recovery, a criterion that was used in a National Institutes of Health remdesivir study. Despite what Gilead hailed as another victory, its stock fell around 4% in Monday trading by publication time.

To take a closer look at the data, among the 191 patients treated for five days with remdesivir, 146 (76%) had at least one point of improvement on a seven-point clinical scale at day 11, whereas 132 (66%) of 200 patients on standard treatment could say that. The scale ranges from hospital discharge to increasing levels of oxygen and ventilation support to death.

Interestingly, treating patients with remdeisivr longer—for 10 days, the drug's original recommended dosage—the benefit shrank in moderate patients to just 31% over standard of care alone. For that regimen, 70% of 193 patients on remdesivir showed at least 1 point of clinical improvement.

Remdesivir has known side effects, such as liver damage. Did safety hold back the drug’s efficacy when used longer? It just may be. Side-effect rates were indeed higher for those patients: Fifty-five percent of those on the 10-day regimen suffered some sort of side effect, versus 51% of the 5-day group and 45% of the standard-of-care group. But the rates of grade 3 and higher events were similar across the three arms at 11%, 10% and 12%, respectively.

Gilead recently expanded the study to add another 1,000 moderately ill patients.

RELATED: Detailed COVID-19 data for Gilead's remdesivir are finally here, confirming its benefits and limitations

Remdesivir has caught global attention as the only drug that has so far shown a clear benefit in large, well-controlled clinical trials. The U.S. FDA granted the drug an emergency use authorization last month, and Japanese authorities have conditionally approved it to target the novel coronavirus. The EMA has put it under rolling review.

The 1,063-patient NIH study showed remdesivir could cut recovery time for hospitalized patients by nearly 32%. Patients on the drug recovered after a median 11 days, four days shorter than those on placebo. But the benefit seen in the overall patient population was largely driven by those who required oxygen supplementation but were not ventilated, and it showed limited effect on outcomes for those with mild or moderate disease.

Gilead has promised to donate its initial supply of about 1.5 million doses of the drug. Previously, the company said the Simple-Severe study showed the drug led to similar clinical improvement for severe patients at either the 5-day course or 10-day regimen. If the treatment length can be reduced, it would mean more patients could get the drug amid constrained supply.