Effectiveness of different border control strategies for reducing mpox importation risk: a modelling study.

Background: The Clade Ib monkeypox virus 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 localised outbreaks in the event of global spread.

Methods: We developed an agent-based model to simulate individual disease progression and testing. We then evaluated the effectiveness of nine border control strategies in reducing importation risk. The simulations incorporated varying disease prevalence levels (0.001%, 0.005%, and 0.01%) in the country of origin.

Findings: 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 pre-departure, on-arrival, and both tests, respectively. Replacing the on-arrival test with a 7-day quarantine and post-quarantine testing would lower the proportion 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.

Interpretation: When disease prevalence in the country of origin is low (0.001%), 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, 7-day quarantining followed by post-quarantine testing, or 28-day quarantining is required to maintain similar effects. Border management will require risk assessments between importation risk, based on origin country prevalence, and the negative impacts of control on travellers.

Funding: This work was supported by Ministry of Education Reimagine Research Grant; PREPARE, Ministry of Health; the Japan Science and Technology Agency (JST) (JPMJPR22R3 to AE); the Japan Society for the Promotion of Science (JSPS) (JP22K17329 to AE), and National University of Singapore Start-Up Grant (to AE); Nanyang Technological University, Singapore-Imperial Research Collaboration Fund (INCF-2023-007 to JTL).