While this year's influenza season is predicted to peak around early February, anybody of any age group, sex or nationality is at risk of infection all the way through March.
While 210,000 children under age 10 accounted for almost a third of the 660,000 flu cases reported in the week of Jan. 13 to 19, another 200,000 patients were made up of people in their 30s and 40s, according to data released by the Health, Labor and Welfare Ministry.
Following are questions and answers on how to prevent the flu and what measures to take if you do come down with it: