COVID-19 therapies made from a cocktail of two types of antibodies were effective against a wide range of variants of the coronavirus in a mice and hamster study, the Washington University School of Medicine in St. Louis reported on Monday.

Antibodies are used to treat cases of COVID-19, often early in the process. Former U.S. President Donald Trump was treated by an antibody cocktail by Regeneron Pharmaceuticals in October after he tested positive for COVID-19.

The latest study included three of the four variants that have been designated "variants of concern" by the World Health Organization, including Alpha, first identified in the UK, Beta, first found in South Africa and Gamma found in Brazil, as well as an emerging variant from India similar to the Delta variant of concern.

The U.S. Food and Drug Administration in April revoked the emergency use authorization of Eli Lilly's single antibody therapy, bamlanivimab, saying there was increased circulation of variants resistant to the therapy when used alone.

Other studies have previously shown that some antibody combination therapies remained potent against those emerging variants of the coronavirus that were resistant to single antibody therapies.

The latest study found that combinations of two antibodies often retained potency against variants even when one of the two antibodies lost some or all ability to neutralize the variant in lab studies.

The study, which was conducted in mice and hamsters, tested all single and combination antibody therapies authorized for emergency use by the FDA against emerging international and U.S. variants of the virus.

The researchers evaluated the FDA authorized combination therapies made by Regeneron, Eli Lilly and a single antibody therapy, sotrovimab, by Vir Biotechnology Inc and GlaxoSmithKline Plc.

They also assessed the antibodies currently in clinical trials by AbbVie Inc, Vir and AstraZeneca.

"Resistance arose with some of the monotherapies, but never with combination therapy," study co-author Jacco Boon wrote.