Influenza: With Hot Temperatures Suddenly Down, Flu Season Has Set in Early

Editorial

15:39 JST, October 16, 2025

The flu season has already begun. Many people may be surprised by this, given that hot temperatures continued until recently. Hopefully, people will stay on the alert and take precautions against the full-fledged spread of influenza.

The Health, Labor and Welfare Ministry announced that the nation has entered the period for influenza to spread rapidly. This is based on reports from medical institutions nationwide showing an average of 1.04 patients per institution during the week of Sept. 22 to 28, exceeding the threshold of one patient to determine the start of the season.

The following week saw a 50% increase in the number of patients, marking the seventh consecutive week of growth.

As there were few flu cases during the COVID-19 pandemic, many people have weakened immunity to the illness. That led to the flu spreading throughout the whole of 2023 regardless of seasons. Except for that year, this year marks the earliest onset of the flu season in the past decade, according to the ministry.

There are concerns that the number of infections could rise from now, and there is a need for everyone to be more vigilant.

Foreign visitors to Japan may be one reason the flu season has started early. The Osaka-Kansai Expo that was held this year attracted more visitors to Japan. As there are some regions in the world where the flu spreads throughout the year, the virus likely was introduced from overseas.

The effects of extreme heat have also been noted as a factor. Prolonged intense heat led to more time spent indoors in air-conditioned environments. When lots of people spend more time in poorly ventilated, enclosed spaces, it is easier for the virus to spread.

Over 100 elementary and junior high schools and other educational institutions nationwide closed classes due to the flu in September.

From now, comprehensive measures will be essential to curbing the spread of influenza. Basic precautions, such as thorough handwashing and wearing masks in crowded places, must be taken consistently.

Vaccinations began at many medical institutions this month. While vaccines are not a panacea, they help reduce the risk of developing symptoms and becoming severely ill. The effects are said to last about five months.

Vaccines begin to take effect about two weeks after they are given. With the spread of influenza already starting this year, early vaccination is crucial. It is especially hoped that elderly people and those with chronic illnesses, who are at high risk of serious illness, and young children will be quick to get vaccinated.

When the flu was raging from the end of last year into the New Year holiday season, production of some flu medicine was not able to keep pace with the surge in patients, leading to temporary supply suspensions. To prevent patients from feeling anxious, the government should pay attention to the drug supply and request greater production if necessary.

In addition to the flu, other infectious diseases, such as COVID-19 and whooping cough, continue to spread. It is vital that people remain on their guard.

(From The Yomiuri Shimbun, Oct. 16, 2025)