Evaluating the effectiveness of international travel controls to identify MPXV-infected travelers: a simulation study

In August 2024, the World Health Organization (WHO) declared a public health emergency due to the rapid spread of mpox in Africa and beyond. International travel controls (ITCs), such as health screening and viral testing, could help avoid/delay the global spread of MPXV, fostering preparedness and response efforts. However, it is not clear whether the viral tests at immigration are sufficient to avoid introduction 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 polymerase chain reaction (PCR) testing at immigration. The primary outcome was the proportion of MPXV-infected travelers identified under various international travel control policies. To estimate time-varying false-negative rates of PCR tests with different detection limits, we employed viral dynamics models calibrated to data from three anatomical sites: oropharynx, saliva, and rectum. Additionally, we simulated the effects of these control measures on the recommended duration of a post-entry monitoring period. Travelers were assumed to depart from mpox-affected countries, defined as those with ongoing MPXV transmission, potentially representing both historically endemic regions and countries with recent outbreaks.

Our results show that under an endemic scenario, the combination of health screening and PCR testing using saliva swabs identifies approximately 74% of MPXV-infected travelers. Using rectal swabs slightly improves detection, identifying up to 79% of infected individuals. A comparable improvement can also be achieved by increasing test sensitivity (i.e., reducing the detection limit from 250 to 10 copies/mL). Based on the distribution of post-entry incubation periods, we estimated that travelers from mpox-affected regions should self-monitor and adopt precautionary behavior for at least 16 days to mitigate the risk of onward transmission.

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.