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The health ministry on Monday approved a monoclonal antibody-based treatment developed by GlaxoSmithKline PLC and U.S. firm Vir Biotechnology Inc., the second time it has given its OK to a drug for the treatment of mildly and moderately ill COVID-19 patients.

Sotrovimab, which is given as a single dose intravenously, became the fifth medicine approved in Japan for treating COVID-19.

A clinical trial involving 1,057 patients showed that the drug, which was granted emergency use authorization in the U.S. in May, reduced the risk of death and hospitalizations lasting longer than 24 hours by 79% compared with a placebo.

The approval, which comes three weeks after GlaxoSmithKline’s Japan unit submitted the application to the ministry, gives a boost to the arsenal of remedies available to treat mildly to moderately ill COVID-19 patients who do not require oxygen but are at risk of seeing their condition become severe.

Dr. Joe Chiba, professor emeritus at the Tokyo University of Science, said that the drug will expand treatment choices at a time when some high-risk patients, such as those with rheumatoid arthritis or cancer, are not seeing any rise in neutralizing antibodies for the coronavirus despite the completion of a two-shot COVID-19 vaccine regimen, due to the use of immunosuppressive drugs.

“The focus will be on whether the ministry approves the application for the drug to be administered to outpatients, as the overseas trial showed the drug had no efficacy when used in hospitalized patients,” he said.

Since its approval in July, a growing number of hospitals nationwide have already been using the other monoclonal antibody treatment, Ronapreve, which is composed of the artificially produced antibodies casirivimab and imdevimab. The final phase clinical trial overseas showed the drug, which Prime Minister Yoshihide Suga described as “revolutionary” and was developed by U.S. firm Regeneron Pharmaceuticals and Swiss drugmaker Roche, reduces the risk of hospitalization or death by 70.4% and shortened the duration of symptoms by four days.

While Ronapreve’s antibodies were developed from recovered COVID-19 patients, sotrovimab was originally identified during the SARS outbreak in 2003. Sotrovimab binds to a region of the spike protein, which gives it strong efficacy even against coronavirus variants, GlaxoSmithKline says. Data from in vitro studies has shown that sotrovimab maintains activity against currently circulating variants of concern and interest, including the delta and lambda versions, according to the British drugmaker.

Sotrovimab has received an endorsement from the Committee for Human Medicinal Products in the European Union, and has also been granted temporary authorization in Canada, Italy, Singapore, the United Arab Emirates and other countries. In addition, it has received marketing authorization in Australia.

While the efficacy shown in the clinical trial was high, one thing that remains a concern is that a study published in the journal Science has shown that sotrovimab’s neutralizing activity in vitro is markedly lower than Ronapreve's, Chiba said.

“Unlike Ronapreve, sotrovimab binds to SARS and other coronaviruses in general,” Chiba said. “Sotrovimab’s neutralizing activity may be relatively low, but according to Vir Biotechnology, it exhibits potent effector function in vitro, potentially allowing the antibody to engage and recruit the rest of the immune system to kill off already infected cells. It has also shown its efficacy in clinical trials.”

In response, Tokyo-based GlaxoSmithKline KK said in a statement: "This paper focuses on novel neutralization antibodies which they discovered. Since the data in the paper is not head-to-head data comparing sotrovimab … with other (monoclonal antibodies), GSK is not in the position to comment."

Chiba said that the development of a slew of other antibody treatments is underway, including a promising one developed domestically by researchers at the National Institute of Infectious Diseases and Hokkaido University.

“Rather than relying on overseas drugs, I would like the government to push the commercialization of domestic antibodies that would be able to neutralize a new coronavirus that may emerge in the future,” he said.

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