SAPPORO -- As Japan's northernmost prefecture of Hokkaido has seen a spike in the number of coronavirus infections mainly around its capital Sapporo since late October, experts have warned that the trend was spurred by wintry dryness and increased human traffic due to the national government's "Go To" demand boosting campaigns among other factors.
Sapporo has seen a spate of coronavirus cluster infections in its famed entertainment district Susukino since September, and clusters have also begun to be reported in various areas across Hokkaido almost daily since the beginning of November.
One factor behind the rapid spread of infections is believed to be greater human traffic stimulated by the central government's Go To campaigns to stimulate domestic demand for pandemic-hit businesses. According to Hokkaido Airports Co., which operates airports in the prefecture, the number of passengers on domestic flights at New Chitose Airport near Sapporo plummeted to 110,697 in May, down 93.7% from the same month in 2019 and a record low so far this year. Since June, however, figures gradually picked up, and the number of domestic flight users rose to 577,164 in July, when the first batch of the Go To campaigns was ushered in, but it was still a 68.9% drop from a year earlier. In September, the figure improved to 799,662, though still a 59.2% decrease from the year before.
Noritsugu Tose, professor of cell physiology at Sapporo Medical University, points out that the four-day weekend in September "was one of the turning points for the spread of infections." Even with the effects of the Go To campaigns and other factors, authorities "had managed to curb infections thanks to efforts by public health centers and other parties, but they gradually became unable to contain infections from September. Since mid-October, all they've been able to do is just follow up on clusters, and authorities are far from catching up with the spread of infections."
Professor Tose cites wintry dryness as another factor behind the spread of infections. In reference to the characteristics of viruses generally becoming rampant in winter, he said, "As winter has set in, the air has become drier, sparking the spread of infections in Hokkaido."
It has been known that "aerosol" particles floating long in the air contributed to many of the coronavirus infection routes. When Riken and other research institutions used the supercomputer Fugaku to study the relationship between the spread of droplets and humidity, it turned out that more than twice as many aerosolized droplets from a person's cough reached another person sitting 1.8 meters across in 30% humidity compared to an environment with 60% humidity.
In Sapporo, where the number of coronavirus cases spiked in September and accounts for about 70% of all cases in Hokkaido, the minimum humidity has dropped, suggesting that the increase in coronavirus cases coincides with the progress of dryness.
As part of measures to prevent infections at households and workplaces during winter, Tose says, "The most important thing is not to bring viruses into those places. I would like people to make sure that their family members take basic measures properly such as wearing masks and washing their hands. It is effective to thoroughly ventilate offices and stores with air conditioners on, even though it's costly."
(Japanese original by Junichi Tsuchiya, Hokkaido News Department)