Less than a month after the first few cases of a new respiratory illness were reported in Wuhan, China, travelers have carried the virus to at least four other countries, including the United States. More than 500 people are known to have been infected, at least 17 have died — and the world is bracing itself for what might come next.

On Wednesday, experts at the World Health Organization decided to postpone until Thursday a decision on whether the current outbreak constitutes a “public health emergency of international concern,” a label given to serious public health events that endanger international public health” and “potentially require a coordinated international response.”

A vote by W.H.O.’s emergency committee was split down the middle, its chairman said, and the group concluded that it did not have enough information to make a decision.

“The decision about whether or not to declare a public health emergency of international concern is one I take extremely seriously, and one I am only prepared to make with appropriate consideration of all the evidence,” Dr. Tedros Adhanom Ghebreyesus, W.H.O.’s director general, said at news briefing.