Study finds low risk of international Ebola virus transmission

In previous Ebola disease outbreaks in Africa as well as the current outbreak of Ebola disease caused by Bundibugyo virus in the Democratic Republic of the Congo, immediate neighbouring countries are most affected when it comes to cross-border spread. As decision-makers outside Africa may be considering border and travel policies to interrupt pathways for international transmission, van Zandvoort et al. identified and analysed all known Ebola disease cases outside Africa to assess the risk of undetected Orthoebolavirus transmission outside Africa and to put it into context with possible border and travel policies. 

The authors searched for all laboratory-confirmed Ebola disease cases that presented outside of Africa since 1976 to date across scientific articles, public health bulletins and news reports including cases due to Bundibugyo, Ebola and Sudan virus outside Africa with exposure in Africa and subsequent travel outside the continent, as well as cases with exposure outside Africa.

Two types of exported cases: medical evacuation and latent

In total, the search yielded 28 identified confirmed Ebola disease cases outside Africa during the period 1976 to May 2026 with 25 primary imported cases and three secondary cases infected by another patient in the United States (US) or Europe.

The analysis distinguishes between two types of primary exported cases. On the one hand the analysis included people who were medically evacuated, i.e. securely transported by air ambulance for treatment outside Africa following a confirmed infection. On the other hand, latent cases were defined as people who developed symptoms during or after their return from the outbreak region on a commercial flight. While the first group represents a known risk with the possibility to mitigate transmission risk with strict measures, the second group requires diagnosis and isolation.

Most of the identified cases (27) occurred during the 2014–16 Ebola virus epidemic in Western Africa and one during the ongoing 2026 Bundibugyo virus outbreak. The authors detected four latent cases, all of which were exported during the 2014–16 Ebola disease epidemic. These four cases were among 300,000 travellers who underwent screening at the time. However, all four were asymptomatic (and hence undetectable) at the point of both exit screening and entry screening. Three were returning healthcare workers responding to the epidemic and one had helped a pregnant person obtaining medical assistance.

Low overall risk of exportation

Based on these data, according to van Zandvoort et al., the crude overall risk since the year 2000 was 0.17 Ebola disease cases outside Africa per 1,000 reported cases in Africa (excluding medically evacuated cases). The authors conclude "our results suggest overall that the risk of case exportations is low and could be substantially mitigated by infection prevention measures at the outbreak source and among outbreak response workers, in concert with enhanced travel screening and monitoring for returning response workers, as recommended in WHO border and travel guidance for the current outbreak.

The authors thus have the view that "as exit screening in an outbreak-affected country aims to reduce case importations in other countries, it is a shared international responsibility. This may be best supported by strengthening local capacity for such screening."