Shares of Vir Biotechnology Inc. /zigman2/quotes/214486077/composite VIR +2.63% gained 1.3% in premarket trading on Friday, the day after the biotech and GlaxoSmithKline /zigman2/quotes/209463850/composite GSK -0.74% said they started dosing patients in a late-stage clinical trial for an experimental antibody-based COVID-19 treatment. The Phase 3 study is part of the National Institutes of Health's Accelerating COVID-19 Therapeutic Interventions and Vaccines Program. The companies are testing VIR-7831 in patients who have been hospitalized due to COVID-19 infections. The investigational treatment "has the potential to neutralize the virus and kill infected cells, [which] could allow this treatment to be effective for patients in hospital settings, where other antibodies have so far not shown an impact," GSK chief scientific officer Dr. Hal Barron said in a statement. While at least two coronavirus vaccines have showed an efficacy rate of about 95% in clinical trials, making them highly effective at preventing symptomatic forms of the disease, efforts to develop treatments for the disease have been less successful so far. One drug, Gilead Sciences Inc.'s /zigman2/quotes/210293917/composite GILD +0.65% Veklury, has received approval from the Food and Drug Administration as a COVID-19 treatment, though there is some debate about the effectiveness of the treatment. The World Health Organization last month recommended that Veklury should not be used to treat COVID-19 patients. So far this year, Vir's stock is up 158.9%, shares of GSK are down 21.4%, and the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.68% has gained 15.2%.