Quadrivalent human papillomavirus vaccination in boys and risk of autoimmune diseases, neurological diseases and venous thromboembolism

Background: In recent years, human papillomavirus (HPV) vaccination of boys has been added to childhood vaccination programmes in several countries but, so far, no systematic population-based assessment with long-term follow-up has been undertaken of the relative incidence of adverse outcomes following HPV vaccination in this group. We investigated if quadrivalent HPV (qHPV) vaccination of 10-17-year-old boys is associated with any unusual risk of autoimmune diseases, neurological diseases or venous thromboembolism.

Methods: We conducted a national cohort study of 568 410 boys born in Denmark 1988-2006 and followed for 4 million person-years during 2006-16, using nationwide registers to obtain individual-level information about received doses of the qHPV vaccine and hospital records for 39 autoimmune diseases, 12 neurological diseases and venous thromboembolism. For each outcome, we estimated incidence rate ratios (RRs) with 95% confidence intervals (CIs) according to qHPV vaccination status.

Results: Altogether 7384 boys received at least one dose of the qHPV vaccine at age 10-17 years. Overall, RRs were close to unity for the combined groups of autoimmune diseases (RR = 0.96; 95% CI: 0.71-1.28, n = 46 cases in qHPV-vaccinated boys) and neurological diseases (RR = 0.67; 0.41-1.10, n = 16), as well as for venous thromboembolism (RR = 0.88; 0.33-2.35, n = 4). After taking multiple testing into account, none of the 52 individual outcomes studied appeared to occur in excess among qHPV-vaccinated boys.

Conclusions: Although additional large-scale epidemiological studies are warranted, our findings provide population-based reassurance that qHPV vaccination of 10-17-year-old boys is unlikely to be associated with an elevated risk of autoimmune diseases, neurological diseases or venous thromboembolism.