BACKGROUND: Approved in 2006, human papillomavirus (HPV) vaccines were initially targeted for girls aged 9-14 years. Although the safety of these vaccines has been monitored through post-licensure surveillance programmes, cases of neurological events have been reported worldwide.
PURPOSE: The present study aimed to assess the risk of developing demyelination after HPV immunization by meta-analysing risk estimates from pharmacoepidemiologic studies.
DATA SOURCES: A systematic review was conducted in Medline, Embase, ISI Web of Science and the Cochrane Library from inception to 10 May 2017, without language restriction.
STUDY SELECTION: Only observational studies including a control group were retained. Study selection was performed by two independent reviewers with disagreements solved through discussion.
DATA EXTRACTION: This meta-analysis was performed using a generic inverse variance random-effect model. Outcomes of interest included a broad category of central demyelination, multiple sclerosis (MS), optic neuritis (ON), and Guillain-Barré syndrome (GBS), each being considered independently. Heterogeneity was investigated; sensitivity and subgroup analyses were performed when necessary. In parallel, post-licensure safety studies were considered for a qualitative review. This study followed the PRISMA statement and the MOOSE reporting guideline.
DATA SYNTHESIS: Of the 2863 references identified, 11 articles were selected for meta-analysis. No significant association emerged between HPV vaccination and central demyelination, the pooled odds ratio being 0.96 [95%CI 0.77-1.20], with a moderate but non-significant heterogeneity (I2 = 29%). Similar results were found for MS and ON. Sensitivity analyses did not alter our conclusions. Findings from qualitative review of 14 safety studies concluded in an absence of a relevant signal.
LIMITATIONS: Owing to limited data on GBS, no meta-analysis was performed for this outcome.
CONCLUSION: This study strongly supports the absence of association between HPV vaccines and central demyelination.