Prevalence of Human Papillomavirus Infection by Number of Vaccine Doses Among US Women

These findings support previous observational studies and post hoc analyses of vaccine trials that demonstrated comparable effectiveness of 1 dose to 2 or 3 doses. The limitations of our study include a cross-sectional design that precluded us from evaluating the timing of HPV vaccination compared with potential exposure. Furthermore, any conclusion regarding efficacy by individual number of doses cannot be drawn given the self-reported immunization history that may be prone to recall bias. If ongoing trials confirm sufficient efficacy and sustained duration of protection from a single-dose regimen, vaccine initiation (as opposed to the series completion) will become a more achievable metric of population coverage.