Vaccination coverage and pertussis trends in Australia, 1995-2024: A Bayesian state-space analysis

Pertussis continues to pose a public health challenge despite high vaccination coverage. Quantifying the population-level impact of vaccination is critical for guiding effective control strategies.

We analysed national and state-level pertussis incidence in Australia from January 1995 to December 2024 using surveillance data. Associations between childhood diphtheria-tetanus-pertussis (DTP) vaccination coverage and incidence were estimated using time series Poisson and negative binomial regression models. Bayesian negative binomial state-space (NBSS) models were applied to characterise temporal dynamics and reconstruct incidence trends.

Pertussis incidence showed recurrent epidemic cycles, with a peak in 2011 (173 per 100 000 per year), a marked decline during 2020-2021 (2 per 100 000 per year), and resurgence from 2023. School-aged children (5-14 years) consistently experienced the highest incidence, while infant incidence declined after 2015. Each 1% increase in infant (1-year) vaccination coverage was associated with a 22% reduction in incidence (incidence rate ratio [IRR], 0.78; 95% CI, 0.69-0.87), and each 1% increase in 5-year booster coverage corresponded to a 5% reduction in incidence (IRR, 0.95; 95% CI, 0.92-0.98). NBSS models effectively captured long-term and seasonal patterns, though uncertainty was greater in low-incidence jurisdictions.

Modest increases in childhood vaccination coverage are associated with substantial reductions in pertussis incidence. These findings provide quantitative evidence for immunisation strategies and emphasise the importance of maintaining high coverage across all childhood milestones.