Incidence of Recurrent Respiratory Papillomatosis (RRP) in Denmark and Sweden During 2000-2023: Two Nationwide Cohort Studies in Children and Young Adults

Introduction: Recurrent respiratory papillomatosis (RRP), primarily caused by human papillomavirus (HPV) types 6 or 11, is a rare but high-morbidity condition. Nationwide estimates of the incidence of RRP are scarce, and we aimed to estimate the incidence of RRP among children and young adults in Denmark (2000-2023) and Sweden (2000-2021). Methods: Using the Danish Pathology Register and the Swedish Patient Register, we identified all individuals with a first-time occurrence of RRP (definition in Denmark: histologically confirmed, topography code T24 plus SNOMED codes for papillomas; Sweden: International Classification of Diseases-10 code D14.1A for papillomas). Incidence rates were calculated as number of RRP cases per 100 000 person-years (py), stratified by country, sex, and age groups at onset (0-14/juvenile 15-29/adult). Trends in incidence were evaluated in the period before and after introduction of HPV vaccination using Poisson regression to estimate the annual percentage change (APC) and 95% confidence intervals (CI). Results: We found juvenile-onset RRP incidences of 0.14 to 0.20/100 000 py as well as adult-onset RRP incidences at 0.19 to 0.40/100 000 py for women and 0.52 to 0.68/100 000 py for men in the postvaccine introduction period. Danish data showed a decreasing trend in RRP during the period following implementation of HPV vaccination, especially among young adults (women: APC = −11.5 [95% CI, −20.9 to −0.9]; men: APC = −11.0 [95% CI, −16.6 to −4.9]), whereas Swedish data did not show any clear decrease in RRP over time. Conclusions: The incidence of RRP is decreasing in Denmark but not in Sweden. This may be the result of more intense HPV vaccination programs, in particular early catchup vaccination of young adults, in Denmark as compared to Sweden.