Keywords: HPV, vaccine effectiveness, propensity score
This study examined effectiveness of HPV vaccination by dose number and dose interval against incident genital warts in a cohort of 64,517 women during 2006-2012. Our study population was insured women with varying compliance to the 3 dose HPV vaccine series, providing an ideal effectiveness study. Exposure groups of interest were 0, 1-dose, 2-dose <6 months apart, 2-dose =6 months apart, and 3-dose groups. Propensity score weights were used to balance baseline group differences. To account for latent genital warts before vaccination, 6-month and 12-month buffer periods from last and first vaccine dose, respectively, were applied. Propensity score-weighted incidence rate per 100,000 person-years was 762 among the unvaccinated. Using 6-month and 12-month buffer periods, respectively, incidence rates were 641 and 257 in 1-dose, 760 and 577 in 2-dose (<6 months), 313 and 194 in 2-dose (=6 months), and 199 and 162 in 3-dose vaccines. Vaccine effectiveness was 68% and 76% in 2-dose (=6 months) and 77% and 80% in 3-dose vaccinees compared to unvaccinated. Neither 1-dose nor 2-dose (<6 months) showed significant effectiveness compared to unvaccinated.