Timeliness and Equity: An Analysis of Measles Herd Immunity in a Regional Area of Australia

Global declines in immunisation rates and a resurgence in measles pose a threat, even in countries like Australia that have achieved elimination status. National coverage in Australia is measured at static timepoints, so it is unclear at what age children received their vaccines. This may permit the emergence of immunity gaps, leaving children susceptible to measles between those reporting timepoints.

A cross-sectional retrospective analysis was conducted using routinely collected data from the Australian Immunisation Register for children residing in Hunter New England Local Health District (HNELHD), New South Wales, born from 1 January 2015 to 1 June 2019 as a quality improvement initiative. Coverage, age at immunisation, and on-time immunisation were described by demographic, local geographic and age variables. Reverse survival analysis was conducted to determine the timing of achieving 95% MCV2 coverage. To ensure the cultural integrity of the research, an Aboriginal researcher co-led the design, analysis and interpretation of results.

The analysis included 53,390 children. Measles coverage exceeded the national and international target of 95% MCV2 coverage, with coverage in Aboriginal children surpassing national rates for all children. Pockets of low coverage were identified in several smaller geographic areas and subpopulations. Median age of MCV1 receipt was 375 days (IQR: 369-390 days), and MCV2 was 560 days (IQR: 551-583 days). More recent birth cohorts had earlier immunisation. On-time immunisation rates were high, and most children receiving measles immunisation late were still immunised within six months of the schedule date. The 95% MCV2 coverage threshold was achieved at 1582 days of age.

Robust measles immunisation coverage and timeliness were found in HNELHD, Australia. Timeliness data analysis is a useful adjunct to static coverage data in understanding immunisation protection. Improving immunisation data availability, accessibility, and timeliness offers potential to better inform targeted public health activity.