Socioeconomic predictors of referral to a diagnostic centre on suspected adverse events following HPV vaccination

Background: In Denmark, the human papillomavirus (HPV) vaccines have been suspected of adverse events since 2014. However, as no causal associations between the HPV vaccines and numerous diseases have been demonstrated, factors prior to vaccination may influence the risk of suspecting the HPV vaccines of causing symptoms. We studied the associations between individual and parental socioeconomic characteristics and the risk of referral to a diagnostic centre in a female population aged 11-29 years with a first HPV vaccination in January 2008 to June 2015. Methods: Individual and parental data from national registries were linked using the unique personal identification number. Logistic regression analyses were used to estimate crude and adjusted odds ratio's according to each individual and parental socioeconomic factor with two-sided 95% 95% CI. Results: The cohort consisted of 453 216 individuals of which 1316 (0.29%) were referred to a diagnostic centre in 2015. Having a mother outside the workforce or an unemployed mother was associated with an increased risk of referral, while girls and women who had fathers with a higher educational level were less likely to be referred. In addition, women aged 20-29 years who were unemployed or outside the workforce prior to vaccination had increased odds of being referred to a diagnostic centre. Conclusion: We found social inequality in the referral to a diagnostic centre following HPV vaccination. This might be explained by an increased morbidity in girls and women of lower socioeconomic status.