Vaccine

BackgroundTo investigate concerns about a potential association between quadrivalent human papillomavirus vaccination (HPV4) and venous thromboembolism (VTE), we conducted a self-controlled case series study in adolescents and young adults 9\ue2\u20ac\u201c26 years of age in the Vaccine Safety Datalink.MethodsWe identified potential VTE cases diagnosed in 2008 through 2011 who had also received at least one HPV4 dose during that period. We confirmed each presumptive diagnosis by medical record review. We calculated incidence rate ratios (IRRs) and 95% confidence intervals (CI) to estimate the risk in the 1\ue2\u20ac\u201c60 day period following HPV4 exposure and in subsets of that period. IRRs were stratified by age, gender, hormonal contraceptive use, and recent surgery or trauma.ResultsWe identified 313 potential cases of VTE among HPV4 vaccinees, and 291 (93%) had sufficient medical records for review. Of these, we confirmed 156 (54%) cases. VTE was uncommon among males (n = 3) and 9\ue2\u20ac\u201c12 year olds (n = 4). Nearly all confirmed cases (97%) had at least one known risk factor for VTE, including hormonal contraceptive use, obesity, and hypercoagulability. Sixteen (10%) confirmed cases occurred in the 1\ue2\u20ac\u201c60 days following HPV4 exposure. The risk of VTE varied from 1.47 (95% CI: 0.47\ue2\u20ac\u201c4.64) in the 1\ue2\u20ac\u201c7 days following HPV4 exposure to 0.92 (95% CI: 0.54\ue2\u20ac\u201c1.57) in the 1\ue2\u20ac\u201c60 days following vaccination. It was not possible to calculate a stratified IRR for males due to small sample size; the other risk factors evaluated did not significantly affect the risk of VTE after HPV4 exposure.ConclusionThe risk of developing VTE among 9- to 26-year-olds was not elevated following HPV4 exposure. Sample size limited our ability to rigorously evaluate potential effect modifiers, such as gender, through stratified analysis.CC999999/Intramural CDC HHS/United States2016-01-13T00:00:00Z26549361PMC471095