Fujifilm Holdings Corp. will continue clinical tests of its anti-flu drug Avigan, a candidate treatment for the novel coronavirus, beyond the initially scheduled end in June due to a lack of sufficient data, a company source said Monday.

Fujifilm planned to finish the clinical tests it started in March in Japan by the end of this month but has seen a delay as recent falls in the number of confirmed infections made it difficult to reach the enrollment target of 96 patients, the source said.

Fujifilm said it does not know when the clinical tests of the drug, developed by its unit Fujifilm Toyama Chemical Co. and also known as favipiravir, will finish.

(Supplied photo shows tablets of the anti-influenza drug Avigan)[Photo courtesy of Fujifilm) 

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The study is being conducted to test the safety and efficacy of the drug in treating COVID-19, the respiratory disease caused by the novel coronavirus.

The Japanese government last month gave up on its target for approval of the drug as a coronavirus treatment in May, after an interim analysis of a separate Avigan clinical study being conducted by a team led by Fujita Health University did not show clear efficacy in treating the disease.

Health minister Katsunobu Kato has said the government will continue to seek swift approval of the drug when its efficacy against the disease is confirmed through clinical tests and studies.

Fujifilm is ramping up production of Avigan, as the government has earmarked about 13.9 billion yen ($127 million) in an extra budget for fiscal 2020 to triple the national stockpile of the drug, enough to treat 2 million people infected with the coronavirus.

As Avigan can inhibit the replication of the virus in cells, experts say it may bring about improvements in those with mild symptoms or those who have recently been infected.

The drug cannot be administered to expectant mothers or women who are likely to become pregnant as it may cause birth defects.