Australia's Measles Immunity Gap
A comprehensive new study led by the National Centre for Immunisation Research and Surveillance (NCIRS) has revealed that an estimated 1.7 million Australians—6.7% of the population—were susceptible to measles in 2019. Published in the Australian and New Zealand Journal of Public Health, the research provides the most detailed picture yet of immunity gaps across all age groups, raising concerns about the nation's ability to prevent future outbreaks.
The study found that overall population immunity to measles stood at 93.3% in 2019, meaning nearly 7 in every 100 Australians lacked sufficient protection. While Australia has maintained its measles elimination status since 2014, the margin for error is thin. The World Health Organization recommends a 95% immunity threshold to achieve herd immunity, and Australia's current level is precariously close to that minimum.
Alarming Trends in Vaccination Coverage
Experts warn that the situation may have worsened since the study period. Childhood vaccination rates have declined in the wake of the COVID-19 pandemic, suggesting that population immunity may now be even lower than the 2019 estimate. This decline is particularly concerning given the global resurgence of measles.
National surveillance data from the National Notifiable Diseases Surveillance System (NNDSS) shows a sharp increase in measles cases in Australia. After recording only single-digit cases annually from 2022 to 2024, notifications jumped to 181 in 2025, and 113 cases have already been reported in the first half of 2026. These imported cases, arriving from countries with ongoing outbreaks, pose a significant risk to under-immunized communities.
Who Is Most at Risk?
The study identified significant variations in susceptibility across different age groups. Infants too young to be vaccinated and adults who may have incomplete vaccination histories were among those with the highest susceptibility. The research combined national immunization register data with multiple serosurveys—the latest conducted in 2012—to produce age-specific estimates, marking the first time such a comprehensive analysis has been attempted internationally.
Lead author Zoë Croker, an epidemiologist at NCIRS, emphasized the importance of these findings: "Our study represents the most comprehensive national estimate currently possible using Australia's most recent serological data and whole-of-population immunization record data." She added, "Australia remains a measles elimination success story, but our findings show we're closer to the minimum level of population protection needed to prevent outbreaks than many people might expect."
Implications for Public Health
The findings underscore the need for targeted vaccination campaigns to close immunity gaps, particularly among adults who may have missed vaccinations in the past or who are unsure of their status. Health authorities are urged to strengthen surveillance and ensure that vaccination services are accessible and promoted, especially in communities with lower coverage.
Measles is a highly contagious viral disease that can cause severe complications, including pneumonia, encephalitis, and death. In 2019, the World Health Organization reported a global resurgence of measles, with over 869,000 cases and 207,500 deaths—the highest in over two decades. Australia's ability to maintain elimination status depends on sustained high vaccination coverage and rapid response to imported cases.
Conclusion
While Australia has been a leader in measles elimination, this study serves as a stark reminder that vigilance is required. The combination of declining vaccination rates and increasing global outbreaks creates a perfect storm for potential resurgence. Public health officials must act now to ensure that the 1.7 million susceptible Australians are protected, before the margin for error disappears entirely.
This article is based on reporting by Medical Xpress. Read the original article.
Originally published on medicalxpress.com
