Japan Issues Flu Alert as Cases More Than Double, Exceeding Outbreak Threshold

Nationwide Flu Alert Declared

Japan's Ministry of Health, Labor and Welfare (MHLW) has officially issued a nationwide influenza alert following a significant increase in reported cases. Data for the week ending November 2, 2025, revealed a total of 57,424 weekly influenza cases across the country, based on reports from approximately 3,000 designated medical institutions.

The average number of cases per medical institution reached 14.90, a sharp rise from 6.29 in the preceding week. This represents an increase of more than double, specifically 2.37 times higher, and critically exceeds the national alert level of 10 cases per institution. Surpassing this threshold indicates a potential major outbreak within the next four weeks.

Widespread Impact and Early Season Start

The influenza outbreak has affected a broad geographical area, with 25 out of Japan's 47 prefectures reporting average case numbers above the alert level. Prefectures nearing the higher 'warning' level of 30 cases per institution include Miyagi (28.58), Kanagawa (28.47), and Saitama (27.91). Other highly affected regions include Chiba (25.04), Hokkaido (24.99), Okinawa (23.80), and Tokyo (23.69).

The current flu season commenced around October 3, approximately one month earlier than the previous year. This marks the second-earliest start since the implementation of the current statistical tracking methods in 1999. The predominant strain identified in the current surge is influenza A.

School Closures and Public Health Recommendations

The escalating situation has led to significant disruptions in the education sector. As of November 2, a total of 2,307 kindergartens, nurseries, and elementary, junior high, and high schools nationwide have implemented partial or full closures to curb the spread of the virus.

Health authorities are urging the public to adopt preventive measures. Recommendations include:

• Wearing masks, especially in crowded settings.
• Practicing proper cough etiquette.
• Frequent handwashing.
• Staying home from school or work if feeling unwell and consulting a doctor.

Reiko Saito, a professor of public health at Niigata University, emphasized that the circulating influenza A strain is 'highly contagious and affects people across a wide range of ages.' Vaccination is strongly encouraged, particularly for vulnerable populations such as the elderly and individuals with underlying health conditions, to mitigate the risk of severe illness.