Why mpox outbreaks can change course and what we can do about it
A new model shows how the mpox virus can shift from transmission among adults to among children over the course of an outbreak. Our responses may need to adapt.
- 9 April 2026
- 5 min read
- by Linda Geddes
At a glance
- Scientists have long sought to understand why, in some settings, mpox cases have clustered among adults and been associated with sexual contact, while in others, infections have been more common among children and spread through household contact.
- A new study provides a potential explanation. By incorporating real-world data on contact patterns and transmission, researchers modelled the spread of clade Ib mpox: a strain that has driven recent outbreaks in parts of Central and East Africa. Their findings suggest that outbreaks can shift naturally between dominant transmission routes, even without changes in the virus itself or human behaviour.
- The findings could have implications for public health responses to mpox outbreaks. They highlight the need for continuous surveillance and for interventions that can be adapted as transmission patterns shift, ensuring control measures remain responsive to how the outbreak is spreading.
Mpox outbreaks may not always follow a single, predictable path. New research based on recent outbreaks of the clade 1b strain suggests the virus can spread through different routes at different stages of an outbreak.
This could mean shifting from sexual transmission among adults to close-contact spread in households and communities over time.
The analysis helps explain changing transmission patterns seen in recent outbreaks and could have implications for how public health officials monitor outbreaks and target interventions, including vaccination.
Whereas early in an outbreak most infections are concentrated among young adults aged 15 to 24, the model suggests that over time a growing share of cases may occur in children.
“Our findings highlight the critical need to adapt intervention strategies to the evolving dynamics of mpox outbreaks,” the researchers said.
Why do mpox outbreaks look so different?
For years, scientists studying mpox have struggled to explain why outbreaks can look so different over time and across regions.
In some settings, cases have been concentrated among adults and linked to sexual contact, while in others more infections have appeared among children through household spread.
Researchers have proposed several explanations, including changes in the virus, waning immunity from past smallpox vaccination and shifts in human behaviour. Mpox viruses are also divided into different clades, which may contribute to these differences.
A new study offers a different way of understanding these shifting patterns. Whereas traditional disease modelling has often focused on a single transmission pathway at a time such as sexual contact or airborne spread, there is growing recognition that many diseases can spread in multiple ways.
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By modelling how mpox spreads through both sexual and nonsexual contact networks, the researchers showed that outbreaks can naturally shift over time from one dominant route of spread to another, even without changes in the virus or in human behaviour.
Dr Fuminari Miura at the National Institute for Public Health and the Environment in Bilthoven, the Netherlands, and colleagues focused on clade Ib mpox, which has driven recent outbreaks in parts of Central and East Africa.
They built a mathematical model incorporating real-world data on contact patterns and transmission, allowing them to explore how the two routes interact and whether this alone could explain the changing patterns seen in recent outbreaks.
Can transmission routes change during mpox outbreaks?
The research, published in Science Advances, found that while sexual transmission may dominate early in an outbreak, nonsexual transmission can become increasingly important over time.
This shift can lead to a wider spread of the virus, particularly into households and among younger age groups.
Whereas early in an outbreak most infections are concentrated among young adults aged 15 to 24, the model suggests that over time a growing share of cases may occur in children, particularly the youngest age groups, potentially leading to higher mortality later in the epidemic.
“Our results suggest that distinct dynamics of clade Ib mpox transmission may be driven by the coexistence of two transmission routes,” the researchers said.
“The dominant route of transmission may shift over time from sexual to nonsexual contacts, which leads to larger epidemics. The age groups contributing most to overall infections and mortality also change over time, suggesting that target groups for intervention should be adjusted accordingly.”
Tracking how outbreaks change over time will also be key, they said. Shifts in transmission could be detected through simple indicators, such as changes in the age of people being infected or patterns in reported contacts.
Monitoring these trends could help health officials spot when an outbreak is moving beyond initial high-risk groups and spreading more widely through communities, allowing them to adapt their response.
“If increasing incidence rates among young children are observed, this may imply that sexually active groups may no longer be the optimal target groups for intervention.
“In contrast, those groups may remain relevant for outbreak responses in countries or regions that are still in their initial phase or have not yet experienced mpox outbreaks,” they said.
What does this mean for controlling outbreaks?
The researchers say their approach could be used to support risk assessments in ongoing outbreaks, including in places where multiple mpox clades are circulating.
However, more evidence is needed to confirm whether these patterns hold in different settings, wrote Prof Samuel V. Scarpino at Northeastern University in Boston, US, in a related Focus.
Future studies will also need better data on how people interact and move, as well as information about the virus itself, to see if similar shifts occur elsewhere and to rule out other possible explanations.
Is multi-route transmission more common than we thought?
Beyond mpox, the findings could also point to a broader shift in how scientists think about infectious diseases.
“The more we look, the more it seems multi-route transmission is the rule, not the exception, for pathogens,” said Scarpino.
“From well-established examples like HIV and hepatitis C to more recent discoveries, including Zika, Ebola and mpox viruses, the list of pathogens that transmit readily via at least two routes is growing rapidly.”
Approaches like this, combined with richer real-world data and new modelling techniques, could help explain puzzling patterns in other outbreaks, not only for mpox, but for diseases such as Ebola and Zika that can also spread in more than one way. By doing so it could improve how responses are designed.
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