The influenza season has officially begun, with the average number of patients per clinic topping the threshold of 1.0 in the latest weekly report, according to the Infectious Disease Surveillance Center.
The season is expected to peak around late January to early February, the government institute said Friday.
The season began at its usual time, with the nation's 5,000 or so designated clinics reporting an average of 1.39 patients in the week through Dec. 22, it said.
The type-A Hong Kong strain is the most reported variant so far, with flu activity particularly strong in western regions. By prefecture, Yamaguchi had 5.12 patients per clinic, followed by Kagoshima with 4.67, Kochi with 3.92, Oita with 3.52 and Saga with 3.21.
The Health, Labor and Welfare Ministry is urging people to wash their hands more frequently after going outside and to wear masks when sick to avoid infecting others.
Flu vaccines usually need about two weeks to take effect.