A nation-wide birth year-by-year analysis of effectiveness of HPV vaccine in Japan.

In Japan, the age-adjusted incidence of cervical cancer has been increasing constantly and rapidly among younger women. We set out to accurately confirm the effectiveness of the HPV vaccine in Japan. Data was collected for women born in the fiscal year (FY) 1990 to 1997, who became eligible for their 20-year-old cervical cancer screening between the FY 2010 to 2017. The adjusted incidence of CIN1+ in women born in FY 1990 to 1993, i.e., those who reached the national vaccination target age prior to the introduction of publicly-subsidized HPV vaccinations, referred here after as 'the pre-introduction generation', was 1.42% (242/17,040). The incidence in the 'vaccination generation' (women born in FY 1994 to 1997, i.e., those who were heavily vaccinated as a group when they were of the nationally targeted age of 13-16) was 1.66% (135/8,020). There was no significant difference between these incidence rates. However, our FY birth year-by-year analysis revealed that the incidence of CIN1+ was obviously lower than that predicted based on just the tendency for CIN1+ seen in the pre-introduction generation. Our analysis revealed that the incidence of CIN3+ was obviously lower in the vaccinated generation than in the pre-introduction generation (p=0.0008) . The incidence of CIN was already tending to increase in both the pre-introduction and vaccination generations. The changes in CIN incidence by individual birth FY must be examined to accurately determine the actual affects of the HPV vaccine for reducing mild cervical lesions. This article is protected by copyright. All rights reserved.