Spokeswoman Margaret Harris urged people not to be caught off-guard by resurgent local epidemics and quarantine measures, saying: "If it's anywhere, it's everywhere and people travelling have to understand that."
"This virus is widespread and people have to take that very, very seriously."
The WHO said last month that it would update its travel guidelines ahead of the northern hemisphere summer holidays but they have not yet been released.
In the meantime, travellers should "remember things will change, or may well change," Harris said at a Geneva briefing.
"We're seeing a lot of upticks, a lot of changes in different countries, countries that had successfully shut down their first transmission are seeing second upticks," she added, mentioning Australia and Hong Kong.