Climate and community-level determinants of respiratory syncytial virus notifications among Queensland infants, prior to the introduction of the RSV Mother and Infant Protection Program (RSV-MIPP) immunisation initiative

Background Respiratory syncytial virus (RSV) is a highly infectious seasonal respiratory pathogen and a major cause of morbidity in young children. In Australia, RSV is the leading cause of hospitalisation for bronchiolitis and pneumonia among infants aged < 2 years, with the highest severity observed in early infancy. RSV became a nationally notifiable condition in July 2021, and the national RSV Mother and Infant Protection Program (RSV-MIPP) commenced in February 2024. Baseline data on RSV incidence and its determinants are needed to evaluate the effectiveness of the program and identify populations at greatest risk. Methods Retrospective cohort study with spatial analysis of all RSV notifications among infants aged < 2 years residing in Queensland between 1 January 2022 and 31 December 2023. Data were obtained from the Queensland Notifiable Conditions System. Incidence rates were calculated by age in months, year, epidemiological week, and climate zone. Spatial analysis methods identified postcode areas with high incidence, and associations in climate zones, and community-level characteristics (remoteness, socioeconomic status, average number of children per family household). Results 18,683 notifications were recorded among infants aged < 2 years between 2022−2023 (79.73 per 1,000 in 2022; 84.80 per 1,000 in 2023). Incidence was consistently higher among 1-month-olds (187.0 per 1,000) and 12-month-olds (186.3 per 1,000). Compared to tropical climates, incidence was higher in temperate (aRR 1.26, 95% CI 1.13−1.41) and arid/semi-arid zones (aRR 1.18, 95% CI 1.00−1.38), with differences in timing and magnitude of epidemics between climate zones. Higher incidence was observed in areas with larger family sizes (aRR 1.39, 95% CI 1.13−1.72). Remoteness was associated with lower incidence (aRR 0.89, 95% CI 0.87−0.92). Conclusions In Queensland, infants living in areas with larger family sizes and temperate or arid/semi-arid climates experienced higher incidence of RSV infections. Lower recorded incidence in remote areas may be due to undertesting, lower population density, or lower utilisation of centre-based childcare services. Future RSV-MIPP strategies should prioritise climatic and community-level determinants to facilitate equitable access. There is an urgent need for new strategies to protect infants aged > 6 months as the protection from maternal vaccination and birth dose therapeutics wear off.