TOKYO (Reuters) - Japanese health authorities say it is difficult to determine the efficacy of Fujifilm Holdings Corp’s antiviral drug Avigan as a treatment for COVID-19, Kyodo News reported on Thursday. Fujifilm has been seeking approval for the drug in Japan since October after its late-stage study showed faster recovery time for patients with non-severe symptoms. In its latest assessment, the Pharmaceuticals and Medical Devices Agency raised several concerns, including the fact that doctors were aware which patients had received the drug or a placebo, Kyodo said, citing government sources. The assessment also acknowledged, however, that approving it for COVID-19 would be “meaningful” as treatment options were limited, Kyodo said. The agency’s assessment will serve as key material for the health ministry’s review panel, which is expected to decide on Dec. 21 whether to approve the drug for COVID-19 treatment in Japan, Kyodo added. Fujifilm’s shares fell 3.8% in early trade, while the broader Tokyo market was flat. While nowhere near the severity seen in the United States and parts of Europe, novel coronavirus infections and related deaths have spiked to record highs in Japan in recent days. Infection cases total about 187,000 and deaths reached 2,755 as of Wednesday, according to public broadcaster NHK. Japan has already approved Avigan, known generically as favipiravir, as an emergency flu medicine. But concerns remain, as the drug has been shown to cause birth defects in animal studies.