1. WHO. Vaccines against influenza WHO position paper – November 2012. Weekly Epidemiol Rec 2012;87:461-76.
2. Ministry of Health, Labour and Welfare. The number of hospitalized patients diagnosed with influenza A(H1N1)pdm09 in Japan. Available at: http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou04/rireki/100331-02.html [in Japanese, accessed 13 February 2015].
3. Ministry of Health, Labour and Welfare. The number of live births in Japan. Available at: http://www.mhlw.go.jp/toukei/saikin/hw/jinkou/geppo/nengai11/kekka02.html [in Japanese, accessed 13 February 2015].
4. Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women;Neuzil;Am J Epidemiol,1998
5. Epidemiology: an introduction;Rothman,2002