Madhi said it had come as a "real blow to the entire control system" when it emerged that contaminated surfaces and direct infection were not the biggest problem. "Once we realised it was truly a respiratory pathogen, that changed the game almost completely," he said. "It becomes much more difficult to contain, and mass gatherings are especially dangerous because of this when there isn't enough population immunity. "Anyone who understands respiratory viruses will know that unlike other viruses that are not airborne, it is going to spread quickly, and once it seeds widely, it's almost impossible that it is just going to disappear."