In a recently published study medRxiv* Server, a team of researchers set up various travel restriction scenarios to assess the potential global risk of monkeypox virus (MPXV) introduction.
background
The World Health Organization (WHO) declared MPXV a global health emergency on July 23, 2022. Previously, it was not considered contagious before the onset of symptoms; However, asymptomatic MPXV infections have been identified in several case reports, raising concerns of an outbreak in several countries. More worryingly, MPXV’s average incubation period is barely 8.5 days, up to 21 days in some cases, but that still makes its accidental introduction easy.
Additionally, the global phasing out of smallpox vaccination in the 1980s, which was considered effective against MPXV, now increases susceptibility to MPXV. All countries are at high risk of MPXV importation due to global travel network. The 2022 MPXV outbreak started in the United Kingdom (UK) due to MPXV importation from Nigeria.
As of September 4, 2022, the United States (US), Brazil, the United Kingdom, Spain and France have the highest total number of MPXV cases. Although not a sexually transmitted disease, in these countries it has spread exclusively through men who have sex with men (MSM). Now that air travel is returning to pre-Coronavirus disease 2019 (COVID-19) levels, the International Air Transport Association (IATA) expects passenger traffic to be 69% higher than in 2019. It is possible that these Travelers accidentally cross the border with MPXV infection.
Previously, researchers used mathematical models to simulate transport networks of airlines arriving from Wuhan, China, where the COVID-19 pandemic began, and to quantify the impact of travel restrictions versus import risk.
About the study
In the present study, researchers used a mathematical model similar to that used during the COVID-19 pandemic to estimate the import risk of MPXV. They used public data sources to collect passenger traffic data from 1,680 airports in 176 countries that had reported confirmed MPXV cases.
Researchers estimated passenger volume (PV) on an airplane based on the maximum number of seats on that airplane. Also, they used the airline network to determine the effective distance, i.e. the minimum distance between all possible paths considering the PV-weighted path length and the degree of each node corresponding to an airport.
In particular, the effective distance worked on the assumption that MPXV began to spread from Britain. However, the team also performed sensitivity analyzes using an airline network proximity centrality index to assess the attractiveness of an airport in the model from a PV perspective rather than effective distance.
In addition, researchers estimated import risk based on patterns of domestic and global population movements using a survival analysis technique in which the hazard function was a function of effective distance. They multiplied the PV by 0.93 to estimate domestic travel and by 0.69 for international travel.
To study travel restrictions, the researchers selected those scenarios that reduced passenger traffic to/from countries with detected MPXV cases. Likewise, they focused on the scenarios that increased or decreased global passenger volumes compared to the high and low passenger volumes observed in 2019 and 2021, respectively, independent of MPXV cases.
study results
With flight levels similar to 2022, it was expected that the risk of MPXV import would be significant at multiple locations by December 31, 2022. Regardless of distance from London, UK, sites with large PV and closely associated flights were at higher risk of MPXV importation.
Reducing PV by 50% or 90% from or to countries that already have MPXV imports did not significantly change the MPXV import risk. PV grade had a non-linear effect on reducing MPXV import risk, as connectivity between each airport network also affected the optimal size of volume reduction. PV reduction to minimize the risk of MPXV importation may not be an efficient strategy to make practical recommendations on travel restrictions.
Conclusions
The study model failed to effectively capture the complex dynamics of global disease transmission. However, it showed that air travel restrictions in most areas may not prevent the import of MPXV in real-world environments. The study results underscored the importance of improved surveillance of MPVX in countries at high risk of introducing the virus. In addition, these countries at high risk of MPXV introduction should focus on contact tracing and isolation techniques.
In addition, the study results on travel patterns for public health interventions could be helpful, particularly to understand the risk of observing an emerging disease across the border.
*Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be relied upon as conclusive, guide clinical practice/health behavior, or be treated as established information.
