Monkeypox cases are continuing to rise globally, suggesting that the rare viral illness has been spreading undetected outside of Africa, in non-endemic countries, for quite some time, the World Health Organization said Wednesday.

But despite that indication, health officials assured that the disease that has plagued African countries for decades is unlikely to become a pandemic and mass vaccination is not necessary.

Right now this is an outbreak and outbreaks can be stopped so thats our effort right now, Dr. Rosamund Lewis, WHOs monkeypox technical lead, said at a press conference that outlined the agencys efforts to stop the virus global spread and also support endemic countries that she reminded live with this disease day in and day out.

WHO has counted at least 550 cases in 30 non-endemic countries as of this week. In the U.S., the Centers for Disease Control and Prevention has tallied 18 cases in nine states as of Tuesday, though health officials expect there may be far more. New York City on Wednesday reported two new potential cases with contact tracing underway.