The association of adverse events with bivalent human papilloma virus vaccination: A nationwide register-based cohort study in Finland

Background: A bivalent HPV vaccine (Cervarix®; HPV2, GlaxoSmithKline) was introduced into the Finnish national vaccination programme (NVP) in November 2013 for girls aged 11–13 years with a catch-up for 14–15 year-olds. We evaluated the association between HPV2 and selected autoimmune diseases and clinical syndromes by conducting a nation-wide retrospective register-based cohort study. Methods: First life-time occurrences of the relevant ICD-10 codes in girls aged 11–15 years between Nov-2013 and Dec-2016 were obtained from the national hospital discharge register. Population denominators were obtained from the Population Information System and vaccination records from the National Vaccination Register. Registers were linked using unique personal identity codes. Association between HPV2 and 38 selected outcomes were studied using Cox regression, with age as the main time-scale and the first vaccination dose as the time-dependent exposure. The hazard ratios (HR) with 95%CI were assessed according to the time since exposure (entire follow-up, 0-180/181-365/>365 days). Results: Of 240 605 girls eligible for HPV2 vaccination, 134 615 (56%) were vaccinated. After adjustment for geographical area (6 hospital districts), country of origin (Finnish-born/not) and number of hospital contacts from 9 through 10 years of age, HRs ranged from 0.34 (95%CI 0.11–1.05) to 8.37 (95%CI 0.85–82.54) and HPV2 vaccination was not statistically significantly associated with a higher risk of any outcome during the entire follow-up. Conclusions: This study found no significantly increased risk for the selected outcomes after the HPV vaccination in girls 11–15 years of age. These results provide valid evidence to counterbalance public scepticism, fears of adverse events and possible opposition to HPV vaccination and consequently can contribute to increase HPV vaccination coverage in Finland as well as elsewhere.