Japan Data

Influenza Cases Rising Rapidly in Early Start to the Season in Japan

Health Society Lifestyle

Japan saw record low numbers of influenza cases during the COVID-19 pandemic, but reduced herd immunity has contributed to an unusually early start to the 2023–24 season.

In a typical influenza season in Japan, cases start to slowly rise from around November before peaking from December to January when it is coldest, and then subsiding. However, the outbreak that began at the end of 2022 continued to the summer of 2023 and without cases subsiding completely, the country is now headed for the peak of another season. This abnormal situation is apparent in the below graph, which shows the number of cases starting to increase two or three months earlier than usual.

On September 22, the Ministry of Health, Labor, and Welfare published figures for September 11–17, based on reports from 5,000 designated medical institutions across the country. There were 34,665 influenza cases, which was 1.57 times as many as the previous week, or an average of 7.03 per institution. Okinawa Prefecture and Tokyo and its surrounding prefectures were particularly affected. On September 21, Tokyo issued its earliest advisory since statistics were first collected in 1999, and the following day Governor Koike Yuriko called on citizens to be alert, saying, “There’s a strong chance of a major outbreak over the next four weeks.”

Number of Weekly Influenza Cases at Designated Medical Institutions

The 2020–21 and 2021–22 seasons saw record low numbers of influenza cases. This is thought to be due to the extensive use of masks and washing and disinfecting of hands adopted to contain COVID-19, measures that were also effective against the spread of influenza.

However, the break also led to decreased herd immunity against influenza. The downgrading of COVID-19 to category 5, so that there were no longer recommendations to wear masks, which became a matter of personal choice, and renewed freedom of international travel set up the conditions for a major influenza outbreak.

Seniors, people with underlying medical conditions, and pregnant women are recommended to consider vaccinations. Other useful preparation includes buying painkillers and antifever medicine, and checking the location of the nearest medical institution providing services to outpatients with fevers.

(Translated from Japanese. Banner photo © Pixta.)

influenza COVID-19