A long thread about mpox and the context specific nature of outbreaks prompted by the large outbreak of MPXV Clade IIb happening at the moment in Sierra Leone:
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The reproductive number (R) for mpox virus (MPXV) is very context-dependent because of the route of transmission (close contact) and the long infectious period. In most places it seems that household transmission is very common but between-household is much less so.
This was true for zoonotic infections directly from the non-human reservoir (forest rodents) - and is also the case in the more recent Clade I (a & b) outbreaks in DRC, Uganda and Burundi (the outbreaks which have been best characterised).
What sexual networks provide is a high number of close physical contacts within the infectious period. So you can have many cases without sexual transmission but the sexual network is required to sustain the outbreak.
This means that the initial cases tend to be in young(ish) adults - the gender ratio will depend on the sexual network (the 2022 epidemic was almost exclusively in men). But as these epidemics progress there have been an increasing number of younger people infected due to transmission in household.
There may also be an effect of ascertainment bias as children are more likely to have severe mpox and/or may be more likely to get medical care (in Burundi medical care is free for children under 5).
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