(Reuters) – GlaxoSmithKline and partner Vir Biotechnology have started testing their experimental antibody on early-stage COVID-19 patients, entering the race to find a winner in a promising class of antiviral drugs to combat the pandemic.

The British drugmaker said on Monday the long-acting single injection will be tested on recently diagnosed high-risk cases for its ability to prevent hospitalization, typically a life threatening disease stage.

GSK, which in April moved to invest $250 million in Vir and agreed to collaborate on the antibody, is behind some peers in developing the class.

Regeneron, which is working on antibody manufacturing with Roche, expects initial data from ongoing trials of its COVID-19 two-antibody combination in September.

Eli Lilly, working with biotech firm AbCellera, early this month started testing whether their antibody can prevent the infections in nursing homes. A separate trial testing the compound on recently diagnosed COVID patients may yield initial data in September or shortly after.

“We’re coming into the clinic a little bit later and part of that is because we spent some time selecting what we believe will be a best-in-class antibody,” Vir Chief Executive George Scangos told Reuters.

The antibody is designed to not only block the virus from invading cells but also to recruit immune cells to kill already infected cells, which would otherwise replicate the virus.

It also has been altered to stay effective for several months on a single shot and to cling to a part of the virus’s outer spike protein that has shown no tendency to mutate.

After testing the drug on an initial 20 U.S. participants over two weeks for safety, the trial will expand to 1,300 patients globally.

GSK said initial results could be available by the end of the year, complete results during the first quarter of 2021, and early access to patients could be on the cards before June.

GSK’s more prominent role so far in combating the pandemic has been in providing adjuvants, efficacy boosters that play a vital role in many vaccines.

The global effort to develop a vaccine against the virus, which has so far claimed more than 800,000 lives globally, has seen recent launches of late-stage trials, but work on treatments has also gone into overdrive.

While one approach has been to quell a dangerous overreaction of the immune system, known as cytokine storm, another has been to block the virus from invading cells with antibodies.

Antibodies, part of the body’s adaptive immune system, are normally made by white blood cells in response to a foreign substance in the body.

But pharma companies, also including AstraZeneca and Molecular Partners, are working on manufactured monoclonal antibodies, made in bioreactors from living cells, for a more targeted attack on the virus.

Using plasma from recovered COVID-19 patients, which contains a range of antibodies, is a similar approach but it may be fraught with more complex logistics and less consistent quality than manufactured antibodies.

In future studies, GSK and Vir plan to run more trials on their antibody’s ability to prevent the infection and treat patients that are already in hospital care. Later this year, they plan to start a trial of a second antibody from the collaboration.

(Reporting by Ludwig Burger; editing by David Evans)