National data reveal vaccination coverage far below survey estimates, with clinicians urged to act before the next surge.
Australia’s mpox response faces a critical inflection point after national surveillance data exposed a substantial immunity gap among gay, bisexual and other men who have sex with men (GBMSM).
Findings from the new Australian study suggest both epidemiological blind spots and missed vaccination opportunities across the health system.
“These findings suggest a major immunity gap within the broader at-risk population in Australia,” said Associate Professor Frank Beard, associate director at the National Centre for Immunisation Research and Surveillance (NCIRS) and a senior author of the study.
“Australia had an excellent response to the 2022 mpox outbreak, achieving high rates of targeted vaccination and low transmission. However, waning vaccine immunity and low overall vaccination coverage likely reduced population-level immunity and contributed to the 2024 outbreak.”
Drawing on linked analyses of the National Notifiable Diseases Surveillance System and the Australian Immunisation Register, the study, published in eClinicalMedicine,provides the most detailed picture yet of mpox transmission, severity and vaccine uptake in Australia between 2022 and 2024.
It confirmed 1579 notified cases over the period, with 98.9% laboratory-confirmed and 89.2% of symptom onset occurring during the 2024 surge, underscoring the scale and recency of the second outbreak.
Transmission patterns shifted markedly over time, the researchers found. In 2022, two-thirds of cases were acquired overseas, reflecting importation during the early global outbreak.
By 2024 that proportion had dropped to just 3.1%, indicating sustained domestic transmission.
The vast majority of infections were among men, with 85.6% occurring in those aged 20–49 years and a peak in the 30–39-year age group, aligning with sexual network dynamics identified in earlier international outbreaks.
Previous Australian research showed that people who receive mpox vaccination were more likely to have strong social and community connections within GBQ+ networks, while MSM who do not identify as GBQ+ may be less engaged with sexual health services. This may reduce their exposure to mpox risk messaging and awareness of free vaccination opportunities.
“Men who have sex with men who are less connected to community networks and sexual health services may be missing vaccine information and access, which can leave them more vulnerable to infection and contribute to ongoing outbreak risk,” said Professor Beard.
Where behavioural data were available, transmission was overwhelmingly linked to male-to-male sexual contact: among cases with adequate exposure data, 95.3% reported recent sexual contact with a cisgender male partner.
However, more than half of all notifications lacked complete exposure data, highlighting a persistent surveillance gap that limited precise risk stratification and targeting of interventions, the researchers wrote.
Vaccination status among cases further illustrated the protection gap. Nearly half of all cases (45.2%) were unvaccinated, 12.7% had received a single dose, 23.9% had received two or more doses, while 18.2% had unknown vaccination status.
Although the proportion of cases with at least one recorded dose increased from 19.6% in 2022 to 36.7% by the end of 2024, this rise lagged behind the scale of the outbreak.
At the population level, 114,966 vaccine doses were administered to 66,982 individuals over the study period, with 70.9% completing a two-dose course.
Uptake was heavily concentrated geographically and demographically, with 88.4% of recipients living in major cities and more than half in inner metropolitan areas of Sydney and Melbourne.
New South Wales and Victoria accounted for more than three-quarters of recipients. General practice delivered the largest share of vaccinations (43.7%), followed by public health units and hospital-based services, including sexual health clinics.
The temporal pattern of uptake reveals a reactive rather than sustained program. Monthly vaccination peaked sharply in November 2022 at 12,810 doses following the initial outbreak, then declined to low baseline levels before rising again during the 2024 resurgence, with a lower peak of 7119 doses in October 2024.
This suggested waning perceived risk and highlighted missed opportunities for inter-epidemic catch-up vaccination, the researchers said.
Among behaviourally defined MSM aged 16–69 years, full vaccination coverage was estimated at 9.6%, rising to 15.0% when using a sexual identity-based denominator of GBQ+ men.
Age-specific disparities were pronounced. Coverage was highest among men aged 40–49 years, reaching up to 29.5% in GBQ+ estimates but dropped sharply in younger groups, with just 1.0%–1.5% of those aged 16–19 years fully vaccinated and under 10% in those aged 20–29 years.
Jurisdictional variation was also evident, with the highest estimated coverage in the Australian Capital Territory and New South Wales and the lowest in South Australia, although wide confidence intervals reflected uncertainty in smaller populations.
The study also shed light on how vaccines were delivered. Early in the rollout, intradermal administration accounted for more than three-quarters of doses in 2022 as a dose-sparing strategy during global supply constraints, but by 2024 subcutaneous administration dominated (91.1%), reflecting improved supply and evolving clinical guidance.
The authors noted that even these low coverage estimates may be inflated by incomplete reporting. Mpox vaccination is not mandatorily reported to the Australian Immunisation Register, and one state-based analysis found that nearly one in five self-reported fully vaccinated cases had no corresponding registry record.
Overseas vaccinations and earlier concerns about privacy linked to immunisation certificates may have further reduced reporting completeness.
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With Australia currently experiencing low transmission, the researchers said this created a strategic window to close the immunity gap.
Without sustained improvements in coverage, surveillance completeness and targeted communication, the study suggested the country risks repeating the conditions that enabled the 2024 outbreak, this time with a still largely susceptible population.
Scientia Professor Andrew Grulich from the Kirby Institute at UNSW Sydney, and co-author of the study, said that mpox vaccination should be routinely integrated into sexual health care, alongside other recommended vaccines for GBMSM, including hepatitis A and B, human papillomavirus and meningococcal vaccines.
“Mpox vaccination should be offered opportunistically to all sexually active gay and bisexual men and other men who have sex with men wherever they receive care – including general practice and sexual health clinics,” he said.
The study also highlighted the importance of clear, consistent messaging, delivered through trusted community channels, to increase awareness that mpox vaccination was recommended and freely available in Australia.
“Continued national monitoring of mpox epidemiology, vaccine uptake and vaccination coverage among higher-risk groups, including gay and bisexual men and other men who have sex with men, will be essential to inform policy, optimise programs, improve access through targeted communication and prevent future outbreaks,” said Professor Beard.
