We constructed the School Absenteeism Surveillance System (SASSy) and the Nursery School Absenteeism Surveillance System (NSASSy), and proved that thses are quite useful for monitoring of influenza outbreak in schools and it will be gold standard of surveillance for school children in Japan. This study also showed incidence rate of influenza in children at schools, kindergartens, and nursery schools, and proved the highest incidence was in the first grade of the elementary school. This is the first finding using such the huge number of subjects, which is more than 2 million
