New modeling research published in The Lancet estimates that – with no exit screenings in place – three people infected with Ebola will depart Guinea, Liberia or Sierra Leone on an international flight every month.
In August, the World Health Organization’s (WHO) declaration of a “public health emergency of international concern” (PHEIC) in response to the Ebola epidemic in West Africa marked only the third time in the agency’s history that such a declaration has been issued.
The reasons why the PHEIC was issued included the unprecedented scale and geographic range of the epidemic combined with the straining public health resources of the affected countries, the high fatality ratio and the international spread of the virus into Nigeria – Africa’s most populated country.
According to the 2005 International Health Regulations, when a PHEIC is issued, 196 participating countries are obliged to work together to control the epidemic.
To do this, however, decision makers need evidence to objectively determine whether international travel from affected areas will effectively reduce risk in unaffected countries. In the case of the current Ebola outbreak, there have been gaps in the evidence on issues such as this.
Taking into account 2014 worldwide flight schedules, Ebola virus surveillance and health care capacity, the researchers behind the new analysis measure the potential for Ebola to spread internationally via air travel. Crucially, the report addresses how effective air travel restrictions and airport exit and entry screening may contribute to constraining the virus.
“The risk of international spread could increase significantly if the outbreak in West Africa persists and grows,” says lead author Dr. Kamran Khan, of St. Michael’s Hospital in Toronto, Canada. “Risks to the global community would further increase if Ebola virus were to spread to and within other countries with weak public health systems.”
Based on the current status of the epidemic and existing flight restrictions, the analysis finds that, with no exit screening, 2.8 flight passengers infected with Ebola are projected to travel internationally every month.
Despite some airport screening currently being in place in the modeled locations, the report demonstrates the importance of consistently implemented exit screening. As Dr. Khan explains:
“Exit screening at the three international airports (Conakry, Monrovia and Freetown) in Guinea, Liberia, and Sierra Leone should allow all travellers at highest risk of exposure to Ebola to be assessed with greater efficiency compared with entry screening the same passengers as they arrive in cities around the world. However, this will require international support to effectively implement and maintain.”
Analyzing flight patterns in 2013 and 2014, the researchers found that more than half of the 500,000 passengers on commercial flights out of Guinea, Liberia and Sierra Leone flew to five countries: Ghana (17.5%), Senegal (14.4%), UK (8.7%), France (7.1%) and Gambia (6.8%).
In 2014, more than 60% of international travelers are expected to have final destinations in low or lower-middle income countries with limited medical resources. A concern raised by Dr. Khan is that these countries may have difficulty in quickly identifying and responding to imported Ebola cases.
“The best approach to minimize risks to the global community is to control the epidemic at its source,” asserts Dr. Khan.
He explains that while screening travelers arriving at airports outside of West Africa may offer a sense of security, it “would have at best marginal benefits, and could draw valuable resources away from more effective public health interventions.”
In addition, excessive air travel restrictions – the report warns – could destabilize the region through severe economic consequences, potentially damaging essential health and humanitarian services.
“Decision makers must carefully balance the potential harms that could result from travel restrictions against any reductions in the risk of international spread,” concludes Dr. Khan.
The study does not take into account ground travel, which has been responsible for some local transmission between West African countries – such as a recent imported case into Senegal. Also, the analysis does not take into account demographic data for air travelers.
It is possible, for instance, that as people traveling by air are more likely to be of a higher socioeconomic group, they may be at lower risk of exposure than people in lower socioeconomic groups.
Last week, Medical News Today looked at research investigating how widespread a natural immunity to Ebola might be.