Influenza is spreading rapidly in Japan, with the pace of infections being the fastest in the past decade. As the peak period is expected around the year-end and New Year holidays, increased caution is necessary.

This year's outbreak began earlier than usual, at the end of September, and in a single week in late November, approximately 200,000 infection reports were received from about 3,000 medical institutions nationwide. That's an average of 51 cases per facility, which far exceeds the alert level of 30. In the city of Oita's Saganoseki district, an evacuation shelter for victims of a large-scale fire has seen a cluster of flu infections.

Predicting influenza epidemics has become difficult since the COVID-19 pandemic. In 2023, the outbreak extended for an unusually long half a year starting in early September, and in 2024, it spread explosively at the end of the year, marking the highest number of new weekly infections since records began being kept.

It is believed that stringent infection prevention measures during the COVID-19 pandemic, which reduced exposure to pathogens, have contributed to the increase in the number of people without immunity. Other infectious diseases including pharyngoconjunctival fever and hand-foot-and-mouth disease are also experiencing irregular outbreaks.

The record pace of increasing foreign visitor numbers is also cited as a contributing factor. The currently circulating virus is a derivative of the type-A Hong Kong strain, detected frequently in Southeast Asia and Europe since around the summer, and it is believed to have been brought into Japan. Reports indicate this virus has high transmissibility.

In addition to increased human movement, climate change is also a factor in the spread of infections. This year, temperatures dropped rapidly following a scorching summer. This contributed to many elderly residents becoming susceptible to illness, and some individuals contracted the virus before municipalities began their vaccination programs.

Like COVID-19, wearing masks and frequent handwashing are effective preventive measures against influenza. Adhering to these basic personal precautions can prevent health care systems from becoming overwhelmed due to the rapid spread of infections. It also helps mitigate impacts on schools and workplaces.

New vaccine types are also available, including a "painless vaccine" administered via nasal spray, introduced last fall. The Japan Pediatric Society recommends this alongside the injectable type for children.

The national government should proceed with measures assuming the difficulty of predicting outbreaks. A stable supply system for vaccines and treatment must be established during normal times.