Estimating the Burden of Mild-to-Moderate Varicella-Related Infections by Medical Helpline Usage: A Time Series...

In the absence of a national varicella vaccine program, it is assumed that the annual proportion of children in Denmark acquiring a varicella infection (chickenpox) corresponds to the birth cohort size, approximately 60,000 per year. Varicella infections impose a burden on families and increase healthcare utilization. Previous studies have estimated the disease burden of severe varicella cases requiring hospitalization. However, information about the burden of mild-to-moderate varicella cases is scarce. We aim to provide insights into the burden of mild-to-moderate varicella cases at the community level.

We utilized data from the non-emergency medical helpline (1813 helpline) and national hospital admission register to provide adjusted estimates of the burden of moderate varicella cases at the community level among children (< 18 years) in Denmark from 2015 to 2023, applying time series regression analysis to counteract underreporting in the 1813 helpline.

We estimated that 20,439 (95% CI 17,378-23,501) calls to the 1813 helpline were attributed to varicella infections (VZV-associated calls), a 103.1% additional proportion to the 10,068 calls documented in the call notes. The average yearly number of VZV-associated calls was 2271 calls. When correcting for irregular patterns of infection during the COVID-19 pandemic, the average yearly estimated number of VZV-associated calls was 2561. In the first 6 months of 2023, we estimated 2552 calls (95% CI 2170-2934). The overall incidence of VZV-associated calls is 623 per 100,000 person-years (95% CI 529.49-716.06), with annual incidence ranging from 291 in 2021 to 910 in 2017.

The 1813 helpline calls attributed to varicella were double the numbers reported previously in the call notes, indicating a larger impact of mild-to-moderate cases on healthcare services than initially thought. This highlights the importance of addressing challenges with varicella infection burden estimates and adds considerably to the burden of mild-to-moderate cases of varicella on a community level.