OBJECTIVES: To review published data and to describe the burden of influenza virus infection in terms of epidemiology, quality of life (QoL) and economics in Japan.

METHODS: The Medline®, Embase®, and ICHUSHI databases were searched for relevant studies conducted in Japan, from the influenza season 2004/2005 onwards. In addition, influenza-related conference websites were searched to identify relevant conference abstracts presented in 2015/2016. Studies conducted in general population and in patients with influenza or influenza-like illness were included. Outcomes were epidemiological burden such as incidence, hospitalization, mortality, complication and transmission rates, QoL, resource utilisation and costs. The searches were completed with grey literatures such as Japanese guidelines and the MHLW websites.

RESULTS: Estimated annual incidence rates of clinically diagnosed influenza in general population ranged from 9.3% to 13.1% over the period from 2011/2012 to 2016/2017 seasons. Higher incidence rates were observed in children <15yrs (12.4%-21.6%). Hospitalization with influenza diagnosis occurred in 0.6%-41.2% of patients ≤15yrs and in 2.7%-4.9% of patients ≥60yrs. The most prevalent complication was pneumonia in influenza patients requiring hospital admission (12.0%-44.0%). The productivity loss due to influenza was estimated at ¥39,638 per patient. In addition, parents with paediatric patients in primary school age had a substantial productivity loss due to work absenteeism with almost a fifth taking leave at work to care for their children with influenza. Besides, more than 70% of parents with influenza were infected as secondary cases.

CONCLUSIONS: Influenza has a substantial clinical and economic burden in Japan and impacts on a wide population due to a high incidence. Influenza leads to serious complications and hospitalizations, particularly at child's age, resulting in significant productivity losses of their parents. Although the burden of influenza is largely related to complications among elderly people according to international literature, Japanese studies rather highlighted the burden of influenza among children.