Case Numbers Soar as Influenza Season Hits Early in Japan

Infections on the Rise

The Ministry of Health, Labor, and Welfare reported that there were 196,895 weekly influenza cases from November 17 to November 23, 2025, based on data from 3,000 designated medical institutions across the country. This figure is published each week, nationwide; the average number of 51.12 cases per institution was around a third higher than the figure of 37.73 for the previous week.

A total of 39 out of 47 prefectures recorded averages higher than the warning level of 30. Tōhoku was hardest hit, with 89.42 in Miyagi, 86.71 in Fukushima, and 83.43 in Iwate; broadly speaking, averages were up considerably in prefectures from the Kantō region northward. There were partial or full closures at 8,817 kindergartens, nurseries, and elementary, junior high, and high schools nationwide.

The Japan Institute for Health Security has reported that 94% of influenza cases within the five weeks from October 31 to November 23 were of the AH3 subtype, among which the subclade K2 variant is spreading rapidly. As the vaccine for the 2025–26 season is based on a different strain, it is unclear how effective it will be. Preventative measures such as washing hands, ventilation, and wearing masks in crowded spaces are strongly recommended to limit the spread of the disease.

(Translated from Japanese. Banner photo © Pixta.)