Evaluating the Effectiveness of International Travel Controls to Identify Monkeypox Virus Infected Travelers
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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.
Methods
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.
Results
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.
Conclusion
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.
