<p>Recently, efforts have been made to fill a so-called "vaccine gap" between Japan and other countries; however, more work remains. Concerns about adverse events following immunization (AEFI) resulted in an historically passive approach to policy making in the National Immunization Program (NIP). For example, reports of AEFI following human papillomavirus vaccine (HPVV) in 2013 led the Japanese government to withdraw its proactive recommendations, resulting in a sharp drop in HPVV coverage rate to less than 1.0%. In this report, we review key historical incidents that led to the current immunization system in Japan, compare it to that in the United States, and discuss strategies for improving the Japanese immunization system. By strengthening existing policies and programs, such as National Immunization Technical Advisory Groups and AEFI reporting, compensation laws, and immunization education, the remaining vaccine gap in Japan could be filled.</p>