"I think its still early to say," said Nathan Wolfe of Global Virus Forecasting Initiative. "We're still early on in an outbreak like this. One of our main objectives is to try to figure out case mortality rate, what percentage of individuals that it affects does it kill. But what's really a concern is that this virus is clearly spreading from human to human, which is at the point where we become really interested and focus on understanding that."
But if more cases did arise, Schaffner said that a vaccine for the illness would not be available for months.
"It would be an Olympic sprint for vaccine manufacturers, starting today" to have a usable vaccine ready even by October, he said.
"If this is a virus that is sufficiently new -- and that has not been entirely determined yet -- we may need two doses of the vaccine to get protection," Schaffner said. "That, of course, would put additional strain on the vaccine production and delivery services."
ABC News' Dan Childs and Matt Hosford contributed to this report.