"Only one case with a 24-day-long incubation period was found in the 1,099 cases of infection. The chance is less than one in a thousand, so it would be inappropriate to use this rare case to tell the whole story," said Zhong Nanshan, leader of the high-level expert group to fight the virus, who issued a preprint article on medRxiv with his group on Saturday, saying the incubation period for the virus could be as long as 24 days, 10 longer than previously thought.