Japan's COVID-19 cases have fallen sharply. Back in mid-August, Japan hit a peak of more than 25,000 cases in a day. That fell to 151 cases in mid-October, the lowest number since summer last year. The latest figure on Monday was 86 daily cases, with Tokyo reporting just nine new cases. Can we expect similar drops in other parts of the world, or is it just some normal fluctuation? Some Japanese researchers say the virus may be mutating into self-extinction, which could explain the drop. Professor Wu Zhiwei shares his view on that.