Peer-reviewed article
Impact of a single-dose program on varicella hospitalizations and infectious disease inequity in New Zealand: A retrospective cohort study.
Michael-John Fay, Anna S Howe, Elizabeth Wilson, Owen Sinclair, Emma J Best ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001New Zealand introduced a free single-dose varicella vaccine to its national immunization programme in July 2017. This study found that varicella-related hospitalizations in children aged 0-15 dropped by 74% after the vaccine was funded, and complications fell by 83%. Children aged 1-4 years benefited most, with an 88% reduction in hospitalizations. However, Māori and Pacific children still experienced health inequities in vaccination coverage.
Key points
- Varicella hospitalizations fell from 368 to 94 admissions per year after vaccine funding (74% reduction)
- Associated complications decreased by 83%, driven mainly by reductions in infective complications
- Children aged 1-4 years showed greatest benefit with 88% reduction; infants under 1 year had 76% reduction, indicating indirect protection
- Median age of first varicella-related hospitalization was 2 years, with 73% of admissions in children under 5 years
- Māori and Pacific children experienced significant reductions but persistent health inequities in immunization coverage remain
Limitations
The study used retrospective administrative data and did not measure vaccination coverage rates directly, so the relationship between coverage changes and hospitalization reductions cannot be fully quantified. The study does not explain the mechanisms behind ongoing disparities for Māori and Pacific children despite vaccination gains.
Abstract
BACKGROUND: In July 2017, a fully funded single-dose varicella vaccine was introduced to Aotearoa New Zealand's (NZ) National Immunization Schedule. This study assessed the vaccine's impact on hospitalizations, complications, and health disparities. METHODS: A retrospective cohort study was conducted, analyzing varicella-related hospitalizations between 2007 and 2023 for NZ children aged 0-15 years, using national health databases. First varicella-related hospitalizations were identified by ICD-10-AM discharge codes. Incidence rates and subsequent varicella-related complications were compared across varicella vaccine funding periods: before funding (2007-2017), transition (2018-2019), and after funding (2020-2023). FINDINGS: There were 4,946 varicella hospitalizations with a 74% reduction in varicella-related admissions after funding compared to before funding (from 368 to 94 admissions per year). Associated complications decreased by 83%, with infective complications driving this. The median age of first varicella-related hospitalization was 2 years, with 73% of first admissions in children under 5 years. Children aged 1-4 years showed the greatest benefit (88% reduction), followed by infants under 1 year (76%) indicating indirect vaccine protection. Māori and Pacific children experienced significant reductions. INTERPRETATION: The introduction of varicella vaccine on the National Immunization Schedule significantly reduced hospitalizations with varicella and its complications. However, health inequities in immunization coverage remain with Māori and Pacific children disproportionately affected. Efforts to increase vaccination coverage, particularly among underserved populations, are critical to sustaining and enhancing these gains.