Combining mpox vaccination and behavioural changes to control possible future mpox resurgence among men who have sex with men: a mathematical modelling study
BMJ Public Health, vol. 3, pp. e002682
Abstract
ABSTRACT Introduction The 2022 outbreak of mpox subclade IIb in the Netherlands affected primarily men who have sex with men (MSM). Despite the sharp decline in cases, there are concerns about future mpox outbreaks. We investigated the impact of mpox introductions, accounting for vaccination, behavioural changes, and introductions of subclades with different characteristics. Methods We developed a compartmental model for mpox among MSM. We distinguished three levels of sexual activity: low, medium, and high. The group with high activity was the 5% of the population with the highest numbers of sexual partners; the group with low activity was the 60% with the lowest numbers of partners. In the model, individuals were allowed to change sexual activity level. We examined several scenarios with mpox introductions. Results In January 2024, 54% of MSM with high sexual activity level had immunity; this declined to 39% a year later, due to changes in sexual activity. Introduction of 5 cases in May 2025 resulted in 759 cases in the first four months without vaccination after 2023, but the numbers of cases were 34% or 48% lower with 3,000 vaccinations in August-October 2024 or February-April 2025, respectively. With earlier initiation or greater magnitude of behavioural adaptations, the number of mpox cases was 17-51% smaller. Introduction of a subclade with 10% higher transmission probability than subclade IIb resulted in 77% more cases. Conclusions Due to changes in sexual activity, the fraction immune in the group with high sexual activity will decline, leading to greater possibilities for future mpox outbreaks. The number of cases can be reduced with preventive vaccination and behavioural adaptations. Recurring vaccination campaigns should prioritise individuals with high sexual activity level, ensuring those entering high-activity groups are reached. Campaigns promoting timely behavioural changes remain crucial. KEY MESSAGES What is already known on this topic The numbers of mpox cases among men who have sex with men (MSM) in the Netherlands were low in 2023-2024, but there have been many introductions of new cases infected outside the Netherlands. Therefore, there are concerns about future mpox outbreaks, but it is uncertain whether new mpox vaccination campaigns are needed. What this study adds Due to behavioural changes, not-immune MSM enter the group with high sexual activity, thus reducing the fraction immune within the group and increasing the possibility of future mpox outbreaks. Preventive mpox vaccination and behavioural adaptations can impede mpox spread. However, outbreak sizes will increase as the time between vaccination roll-out and new introductions is extended. How this study might affect research, practice or policy Social marketing and interventions promoting timely behavioural changes and vaccination are essential. Recurring vaccination campaigns are necessary for mpox prevention, prioritising individuals with high sexual activity level and ensuring those entering high-activity groups are reached. The findings also emphasize that research is needed to understand determinants of behaviour and monitor behavioural changes over time.
Authors 9
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Maria Xiridou corresponding
National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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Affiliation as printed
Centre for Social Research in Health, UNSW Sydney, Sydney, Australia
Institute for Prevention and Social Research, Utrecht, the Netherlands
Centre for Social Research in Health, UNSW Sydney, Sydney, New South Wales, Australia
Institute for Prevention and Social Research, Utrecht, The Netherlands
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National Institute for Public Health and the Environment · Ehime University
Affiliation as printed
Center for Marine Environmental Studies, Ehime University, Ehime, Japan
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
Ehime University, Ehime, Japan
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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Leiden University Medical Center · National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
Department of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, the Netherlands
Department of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, The Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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Utrecht University · UNSW Sydney
Affiliation as printed
Centre for Social Research in Health, UNSW Sydney, Sydney, Australia
Department of Interdisciplinary Social Science, Utrecht University, Utrecht, the Netherlands
UNSW Sydney, Sydney, New South Wales, Australia
Utrecht University, Utrecht, The Netherlands
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National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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Leiden University Medical Center · National Institute for Public Health and the Environment
Affiliation as printed
Centre for Infectious Disease Control, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
Department of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, the Netherlands
Leiden University Medical Center, Leiden, The Netherlands
National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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