Impact of partial bivalent HPV vaccination on vaccine-type infection: a population-based analysis.

<bold>Background: </bold>Data on the effectiveness of one dose of HPV vaccine are lacking, particularly in population-based settings. Data from a national HPV immunisation catch-up programme of 14-18-year-old girls were used to assess the effectiveness of<3 doses of the bivalent vaccine on vaccine-type and cross-reactive-type HPV infection.<bold>Methods: </bold>Cervical samples from women attending for their first cervical smear, which had been genotyped for HPV as part of a longitudinal HPV surveillance programme were linked to immunisation records to establish the number of vaccine doses (0, 1, 2 and 3) administered. Vaccine effectiveness (VE) adjusted for deprivation and age at first dose, was assessed for prevalent HPV 16/18 and HPV 31/33/45 infection.<bold>Results: </bold>VE for prevalent HPV 16/18 infection associated with 1, 2 and 3 doses was 48.2% (95% CI 16.8, 68.9), 54.8% (95% CI 30.7, 70.8) and 72.8% (95% CI 62.8, 80.3). Equivalent VE for prevalent HPV 31/33/45 infection was -1.62% (95% CI -85.1, 45.3), 48.3% (95% CI 7.6, 71.8) and 55.2% (95% CI 32.6, 70.2).<bold>Conclusions: </bold>Consistent with recent aggregated trial data, we demonstrate the potential effectiveness of even one dose of HPV vaccine on vaccine-type infection. Given that these women were immunised as part of a catch-up campaign, the VE observed in this study is likely to be an underestimate of what will occur in girls vaccinated at younger ages. Further population-based studies which look at the clinical efficacy of one-dose schedules are warranted. [ABSTRACT FROM AUTHOR]