[Published] Accumulation of immunity in heavy-tailed sexual contact networks shapes mpox outbreak sizes
Published:
I summarise our study on the drastic global decline in mpox cases in 2022. This study is now published in The Journal of Infectious Diseases :
🔗 https://doi.org/10.1093/infdis/jiad254
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a couple of key takeaways in the thread below:
Summary
As a quick recap, our earlier work showed that a sexual partnership distribution among MSM where a small number of people have many partners explains the sustained mpox spread.
ON THE FLIP SIDE: these people are the earliest to get infected and immune.
To better understand this impact,
We analysed how the mpox outbreak would be shaped over heavy-tailed sexual contact networks among MSM (i.e. a handful of people have disproportionately many partners) under the baseline scenario without interventions and behavioural changes.
Our mathematical model demonstrates that, with individuals having many partners infected and then immunised in the early phase, Rt plummets, and goes below 1 before 1% of MSM infected when transmission risk per partner is assumed to be 10-30%.
When turning to the empirical data, we found that many countries and US states had experienced an epidemic peak with cumulative cases of ~0.1-0.5% of MSM population, indicating the trends consistent with our model.
Vaccines, contact tracing and behavioural changes may also have brought the peak forward, but our model and the observed peak sizes suggest that the global mpox outbreaks in 2022 would have been anyway self-limiting due to infection-derived immunity.
It is, however, vital to remember that this does not mean there is no need to undertake interventions. To minimise the disease burden, in particular among the most vulnerable population, countermeasures are warranted.
Taken together, our study provides a parsimonious explanation of the observed trends in mpox case by the accumulation of infection-derived immunity in the highly heterogeneous sexual contact networks.
Although the mpox surge seen in 2022 seems over, we need to stay vigilant against the possibility of mpox resurgence given the waning immunity or turnover of individuals at the tail of the sexual partnership distribution.
Finally, kudos to my co-authors!