Border control strategies for reducing importation risk of Clade Ib Mpox
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Background
The Clade Ib monkeypox virus (MPXV), newly identified in the ongoing 2024 mpox outbreak, can be more transmissible through non-sexual routes compared to the previous Clade IIb strain. With imported cases sporadically reported globally, concerns have emerged about the potential of widespread transmission in the general community after importation events. Border control measures, such as screening and quarantining of arriving travellers, may help mitigate this risk and prevent localized outbreaks in the event of global spread.
Methods
We proposed nine border control strategies and evaluated their effectiveness in reducing importation risk using 10,000 microsimulations of individual infection profiles and PCR testing results under scenarios with varying disease prevalence levels (0.01%, 0.05%, and 0.1%) in the country of origin.
Results
The proposed border-control measures would reduce missed cases by 40.1% (39.1%–41.0%), 49.8% (48.8%–50.8%), and 58.1% (57.1%–59.0%) for predeparture, on-arrival, and both tests, respectively. Replacing the on-arrival test with a seven-day quarantine and post-quarantine testing would lower the count to 21.8% (20.9%–22.6%). Quarantine-only strategies showed a linear increase in effectiveness against duration, reaching a 90.4% (89.8%–91.0%) reduction with a 28-day quarantine. Disparities in distributions of missed case counts across strategies would become more pronounced at higher prevalence levels, with stringent approaches like quarantining followed by post-quarantine screening and 28-day quarantine keeping counts below two per 10,000 travellers, even at 0.1% prevalence.
Conclusions
When disease prevalence in the country of origin is low (0.01%), less restrictive approaches such as single on-arrival testing or a 14-day quarantine can maintain very low imported case counts of one or below. At higher prevalences, seven-day quarantining followed by post-quarantine testing, or 28-day quarantining is required to maintain similar effects. Decision makers will face balancing importation risk management and the negative impacts of such interventions to maintain safe international travel.
