Evaluating the Impact of Moderate and Severe Varicella Infections on Danish Children Under 18 Years Old: A Comprehensive Analysis From 2015 to 2023.

Background: Varicella (chickenpox) caused by varicella-zoster virus (VZV) is a highly contagious pediatric disease. While it typically manifests as a mild disease, complications leading to hospitalization are not uncommon. Knowing the current disease burden, seasonality and risk groups is pivotal for evidence-based decisions on the introduction of a varicella vaccine.

Methods: Using the Danish National Patient Register and medical helpline records from the Capital Region, we estimated the burden of VZV infections among children younger than 18 years in Denmark from 2015 to June 2023.

Results: We identified 14,443 cases with annual incidence rates of 325/100,000 children for mild-to-moderate varicella cases (helpline calls), 35/100,000 for moderate-to-severe cases (outpatients) and 10/100,000 for severe cases (hospitalized). Mild cases were most prevalent in children aged 1-4 years, while moderate-to-severe cases were most prevalent among infants <1 year old. Among hospitalized cases, 23.2% had underlying diseases and 47.3% experienced complications. In April 2022, rapid surge in all types of VZV cases occurred, where admissions surpassed the prepandemic level.

Conclusion: This study documents that varicella is highly prevalent among Danish young children. Mild-to-moderately severe cases strain healthcare, causing increased helpline calls and posing a persistent hospitalization risk, especially for infants and children with underlying conditions.