Autoimmune, neurological, and venous thromboembolic adverse events after immunisation of adolescent girls with quadrivalent human papillomavirus vaccine in Denmark and Sweden: cohort study

Abstract

Objective To assess the risk of serious adverse events after vaccination of adolescent girls with quadrivalent human papillomavirus (qHPV) vaccine.Design Register based cohort study. Setting Denmark and Sweden, October 2006 to December 2010.Participants 997 585 girls aged 10-17, among whom 296 826 received a total of 696 420 qHPV vaccine doses.Main outcome measures Incident hospital diagnosed autoimmune, neurological, and venous thromboembolic events (53 different outcomes) up to 180 days after each qHPV vaccine dose. Only events with at least five vaccine exposed cases were considered for further assessment. Rate ratios adjusted for age, country, calendar year, and parental country of birth, education, and socioeconomic status were estimated, comparing vaccinated and unvaccinated person time. For outcomes where the rate ratio was significantly increased, we regarded three criteria as signal strengthening: analysis based on 20 or more vaccine exposed cases (reliability), rate ratio 3.0 or more (strength), and significantly increased rate ratio in country specific analyses (consistency). We additionally assessed clustering of events in time and estimated rate ratios for a risk period that started on day 181.Results Among the 53 outcomes, at least five vaccine exposed cases occurred in 29 and these were analysed further. Whereas the rate ratios for 20 of 23 autoimmune events were not significantly increased, exposure to qHPV vaccine was significantly associated with Behcet's syndrome, Raynaud's disease, and type 1 diabetes. Each of these three outcomes fulfilled only one of three predefined signal strengthening criteria. Furthermore, the pattern of distribution in time after vaccination was random for all three and the rate ratios for these outcomes in the period from day 181 after vaccination were similar to the rate ratios in the primary risk period. The rate ratios for five neurological events were not significantly increased and there were inverse associations with epilepsy (rate ratio 0.66, 95% confidence interval 0.54 to 0.80) and paralysis (0.56, 0.35 to 0.90). There was no association between exposure to qHPV vaccine and venous thromboembolism (0.86, 0.55 to 1.36).Conclusions This large cohort study found no evidence supporting associations between exposure to qHPV vaccine and autoimmune, neurological, and venous thromboembolic adverse events. Although associations for three autoimmune events were initially observed, on further assessment these were weak and not temporally related to vaccine exposure. Furthermore, the findings need to be interpreted considering the multiple outcomes assessed.

To Consent or Decline HPV Vaccination: A Pilot Study at the Start of the National School‐Based Vaccination Program in Sweden

“…Parents want to make a decision they believe is in the best interest of their child 9, 44. The concerns about the vaccine's possible harmful effects on their daughter's future health that we documented are in line with previous research,9, 13, 45 although no adverse effects such as narcolepsy have been linked to the HPV vaccine 41. This highlights the importance of clear and transparent health communication from the government.…”

“…Therefore, we recommend that the information given to parents should be more focused on HPV and the HPV vaccine, including facts about the diseases HPV can cause. Most importantly, the information should clearly state that no adverse effects, such as autoimmune diseases, have been linked to the vaccine 41. It would be a good idea to give parents easily accessible links to evidence‐based information as well as the information distributed by the school health service.…”

Public health value of universal HPV vaccination

“…In post-licensure clinical trials which enrolled 997.585 girls aged 10-17 years old, no serious adverse events ascribable to the vaccine were recorded for the quadrivalent as well as the bivalent vaccine (34).…”

Immunogenicity and Safety of a 9-Valent HPV Vaccine

“…Data have shown that prophylactic HPV vaccination is generally safe and well tolerated. [32][33][34][35][36][37][38] The median age of sexual debut is in the late teens (15-19 years) in most countries. 39 Virginal adolescents (#15 years old) were not included in HPV vaccine efficacy evaluations because of low HPV exposure and ethical constraints.…”