GSK and Vir Biotechnology said on Thursday they are seeking an expansion to the U.S. approval of their antibody-based COVID-19 treatment to include an option for the therapy to be given as a shot in the arm.

The drug, sotrovimab, was authorized for emergency use in the United States in May to prevent mild or moderate cases of COVID-19 from worsening, and is currently being given via an intravenous infusion.

Sotrovimab belongs to a class of medicines called monoclonal antibodies, which are lab-generated compounds that mimic the body's natural defenses. Tests have indicated the drug works against the fast-spreading omicron variant.

The new method of administration, known as intramuscular injection, was shown in a trial to work as well as the standard infusion. It offers more convenience since it can be carried out by family doctors and spare patients a trip to the hospital.

GSK and Vir said on Tuesday the United States had agreed to buy 600,000 more doses of the therapy for an undisclosed sum. Products similar to sotrovimab are being offered or developed by Eli Lilly, Regeneron and AstraZeneca , and so far their administration ranges from infusion, intramuscular shot to an injection under the skin.