Assessing the impact of chickenpox and shingles vaccination using intermittent enhanced surveillance in Queensland, Australia

INTRODUCTION: Chickenpox and shingles are vaccine preventable diseases caused by varicella-zoster virus (VZV). Chickenpox is more common in children before adolescence and shingles among ≥50 years of age. With this study we aimed to determine changes in VZV epidemiology following chickenpox and shingles vaccine introduction in Queensland. METHODS: This case series study used notified cases of VZV infection in Queensland from January 2010 to December 2021. In Queensland, VZV notifications are received as mostly clinically unspecified cases from pathology laboratories. Intermittent enhanced surveillance was conducted using clinician follow up to determine chickenpox and shingles clinical presentation, and we then analysed these by age-group, time period, and within vaccine eligible cohorts. RESULTS: Of the 87,759 VZV notifications received, 70 % (n = 61,298) were notified as unspecified, followed by 23 % shingles (n = 19,927), and 7 % chickenpox (n = 6,534). Over the study period, the percent change in total notifications adjusted by age and sex was estimated to be an increase of 5.7 % (95 % CI 4.9-6.4) each year. The chickenpox notifications fell sharply at 18 months of age (eligible for chickenpox vaccine) with the rate being 57 % and 36 % lower among those aged 18-23 months compared to <12 and 12-17 months of age, respectively. Assuming all cases aged 60 years and older were shingles, notification rates of shingles decreased by 12-22 % among 70-79 years old (eligible for shingles vaccination) over the years 2017-2021 after vaccine introduction in 2016. CONCLUSION: The VZV notification rate has increased over time in Queensland. Impact of chickenpox and shingles vaccines funded under National Immunisation Program is seen with a decline in notification rates among age-specific cohorts eligible to receive the vaccines under the program. Introduction of a second childhood dose chickenpox vaccine and more effective recombinant shingles vaccine may further improve the impact of the vaccination program.