GlaxoSmithKline Plc and Vir Biotechnology said on Monday final results from a late-stage study of their monoclonal antibody confirmed it significantly reduced hospitalisation and death among high-risk Covid-19 patients when given early in the disease.
The treatment, sotrovimab, received an emergency use authorization from the US Food and Drug Administration in May, while the European Union's drug regulator has also backed it.
The drugmakers also said on Monday the US National Institutes of Health (NIH) has recommended sotrovimab to treat high-risk, non-hospitalized patients with mild-to-moderate Covid-19.
The treatment appeared to "retain activity" against current variants of concern and interest, the agency said in its updated guidelines.
In a study of 1,057 patients, sotrovimab resulted in a 79% reduction in risk of hospitalization for more than 24 hours or death due to any cause, the companies said on Monday.
Sotrovimab belongs to a class of drugs called monoclonal antibodies that mimic the natural antibodies the body generates to fight off infection.
Similar therapies developed by rivals Regeneron and Eli Lilly have been approved by US regulators for treating non-hospitalized Covid-19 patients.
GSK said it was now testing sotrovimab as an intramuscular shot, which is more convenient than by intravenous drip, the current mode of administration.
Vir's shares rose about 2% in premarket trading, while GSK's stock was flat.