In retrospect, the authors believed the use of pigs gave the airborne argument an unfair advantage. Pigs could produce significantly more virus than primates, suggesting a greater chance for droplet spread. In addition, because of the massive amount of shedding pigs display when sick, there was a greater opportunity for the monkeys to become infected through the respiratory tract. However, this type of spread is droplet, not airborne. There was no other option than to conclude Ebola was simply not an airborne virus.