Via the excellent blog Controversies in Hospital Infection Prevention, an October 9 post by Eli: Traveling With Ebola Is Not Traveling With Influenza. Excerpt:
Another difference between influenza and Ebola is the incubation period (time from exposure to symptoms). Generally, the incubation period for influenza is 1-4 days (2-day average). For Ebola symptoms appear 2 to 21 days after exposure with an average of 8 to 10 days.
A final difference between Ebola and 2009 H1N1, which seems to be overlooked in discussions of airport screenings and other control measures, is infectivity during the incubation period. Put another way, can you transmit the virus without knowing you are sick?
With Ebola, humans are not infectious until they develop symptoms. In comparison, with 2009 H1N1 it's reported "that pre-symptomatic influenza transmission occurred via both contact and respiratory droplet exposure before the earliest clinical sign, fever, developed" in a ferret model. This finding has been confirmed in humans. Interestingly, SARS is not infectious prior to symptom development (see CDC and Zeng et al), which may explain why we were ultimately able to contain SARS (unlike influenza).
To summarize, Ebola is slower moving, has a much longer incubation period (especially compared to the duration of a transcontinental flight), and is not contagious before symptoms develop. What does this mean? It means that if Ebola was as infectious as influenza, millions would have already died - apocalypse.
It also means that since Ebola is not transmissible during its long incubation period, it may be possible to quickly isolate patients when symptoms develop. Thus, airport screening on exit or entry could limit transmission and perhaps through early diagnosis allow Ebola infected patients to receive life saving treatment more quickly.
A more concrete example: Imagine a person infected yesterday with influenza but still asymptomatic during their two day-incubation period. This person would screen negative overseas and in the US. However, it's highly likely that they are already infectious or will become infectious during their flight. Thus, many other passengers in the airport and plane would take influenza home with them as a vacation souvenir. Screening doesn't work for influenza.
This would not be the case with Ebola because they will detect their symptoms as they become infectious and only spread it though blood exposure - something unlikely so early in the infection even on a long transcontinental flight.
And think about how many times another person has bled on you even when they were bleeding (i.e. the Ebola condition) versus how many times someone has coughed or sneezed on you when they were coughing and sneezing (the influenza condition). **cough**
Airport screening for Ebola symptoms may still be ineffective, but I would like to see a few more mathematical models analyzing the epidemiology of Ebola and the impact of specific screening programs. In the meantime, let's focus our attention and resources on the horrible plight in West Africa.