HPV vaccine: safety, adverse events

British Medical Journal
26 October 2013 (Vol 347, Issue 7930)
http://www.bmj.com/content/347/7930

Editorial
Safety of the quadrivalent human papillomavirus vaccine
BMJ 2013; 347 doi: http://dx.doi.org/10.1136/bmj.f5631 (Published 9 October 2013
Now well established
The prophylactic human papillomavirus (HPV) vaccines are remarkable both for their efficacy against HPV infection and related diseases,1 and for their potential to prevent cervical cancer. Cervical cancer, which is caused by persistent infection with oncogenic HPV types, remains a cause of premature death in women around the world, most of whom have no access to secondary prevention through organised cervical screening programmes.2 The linked study by Arnheim-Dahlström and colleagues (doi:10.1136/bmj.f5906) provides a timely and important contribution to the evidence base on the safety of the quadrivalent HPV vaccine,3 which prevents HPV infection and disease due to the oncogenic types HPV-16 and HPV-18 and types HPV-6 and HPV-11, which cause genital warts.

This population based cohort analysis provides strong evidence that autoimmune conditions, neurological diseases, and thromboembolic disease are not triggered by quadrivalent HPV vaccination. Serious sudden onset conditions such as these, which are largely of undetermined cause, are sometimes falsely attributed to vaccination when population based vaccination programmes are implemented.4 It is crucial that surveillance systems can rule out false associations and identify rare but real …
http://www.bmj.com/content/347/bmj.f5631

Research
Autoimmune, neurological, and venous thromboembolic adverse events after immunisation of adolescent girls with quadrivalent human papillomavirus vaccine in Denmark and Sweden: cohort study
Lisen Arnheim-Dahlström, associate professor1, Björn Pasternak, postdoctoral fellow2, Henrik Svanström, statistician2, Pär Sparén, professor1, Anders Hviid, senior investigator2
http://www.bmj.com/content/347/bmj.f5906

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 assessments