Evaluating the Effectiveness of International Travel Controls to Identify Monkeypox Virus Infected Travelers

Introduction In August 2024, the World Health Organization (WHO) declared a public health emergency due to the rapid spread of mpox in African and beyond. International travel controls (ITCs), such as health screening and viral testing, could help avoid/delay the global spread of the monkeypox virus (MPXV), fostering preparedness and response efforts. However, it is not clear whether the viral tests at immigration are sufficient to avoid importation of MPXV and which samples should be used on the viral tests.

We conducted a simulation study using epidemiological and viral load data to assess the effectiveness of health screening and PCR testing at immigration. This provides estimates of the proportion of infected travelers identified with this policy. Viral dynamics models were used to estimate false-negative rates of PCR tests with different detection limits according to testing regimens at three different sites: oropharynx, saliva, and rectum. We also simulated the effects of these border control methods on the recommended duration of a monitoring period for travelers from mpox-affected regions, during which individuals would self-monitor for symptoms and practice cautionary behavior.

Our results show that the combination of health screening and PCR testing of saliva swabs under an endemic scenario identify only 74% of MPXV infected travelers. The use of rectal swabs combined with health screening allows the identification of a marginally larger share of infected travelers (79%) compared to saliva swabs. A similar identification rate could be achieved by using more sensitive PCR tests (detection limit [DL]: 10 copies/mL vs. 250 copies/mL used in our baseline analysis). We estimated that travelers from mpox-affected areas should monitor themselves and practice precautionary behavior for 16 days.

Health screening and PCR testing at immigration are likely to miss a significant proportion of MPXV-infected travelers, thus a lengthy quarantine period would be required to prevent onward local transmission. Careful consideration on other factors such as economic costs and likelihood of widespread local outbreak will need to be weighed against the adoption of these measures to prevent local mpox transmission given MPXV transmissibility and severity. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was supported in part by the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 Seed Award (RLMOE100201900000001), a Lee Kong Chian School of Medicine startup grant (LKCMedicine-SUG, #022487-00001), and JST, PRESTO (JPMJPR23R3) (to KE). AE is supported by Japan Society for the Promotion of Science (JP22K17329) and JST (JPMJPR22R3). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study used ONLY openly available human data that were originally located at: https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-024-48754-8/MediaObjects/41467_2024_48754_MOESM4_ESM.xlsx I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data availability The data that support the findings of this study are available from the corresponding authors on request.