During a public briefing on Friday, the UN. health agency said there are still many unanswered questions about what triggered the unprecedented outbreak of monkeypox outside of Africa, but there is no evidence that any genetic changes in the virus are responsible.

“The first sequencing of the virus shows that the strain is not different from the strains we can find in endemic countries and (this outbreak) is probably due more to a change in human behavior,” said Dr. Sylvie Briand, WHO’s director of pandemic and epidemic diseases.

Earlier this week, a top adviser to WHO said the outbreak in Europe, US, Israel, Australia and beyond was likely linked to sex at two recent raves in Spain and Belgium. That marks a significant departure from the disease’s typical pattern of spread in central and western Africa, where people are mainly infected by animals like wild rodents and primates, and outbreaks haven’t spilled across borders.

Although WHO said nearly 200 monkeypox cases have been reported, that seemed a likely undercount. On Friday, Spanish authorities said the number of cases there had risen to 98, including one woman, whose infection is “directly related” to a chain of transmission that had been previously limited to men, according to officials in the region of Madrid.

UK officials added 16 more cases to their monkeypox tally, making Britain’s total 106. And Portugal said its caseload jumped to 74 cases on Friday.

WHO’s Briand said that based on how past outbreaks of the disease in Africa have evolved, the current situation appeared “containable.”

Still, she said WHO expected to see more cases reported in the future, noting “we don’t know if we are just seeing the peak of the iceberg (or) if there are many more cases that are undetected in communities,” she said.

As countries including Britain, Germany, Canada and the US begin evaluating how smallpox vaccines might be used to curb the outbreak, WHO said its expert group was assessing the evidence and would provide guidance soon.

Dr. Rosamund Lewis, head of WHO’s smallpox department, said that “there is no need for mass vaccination,” explaining that monkeypox does not spread easily and typically requires skin-to-skin contact for transmission.

No vaccines have been specifically developed against monkeypox, but WHO estimates that smallpox vaccines are about 85 percent effective.

She said countries with vaccine supplies could consider them for those at high risk of the disease, like close contacts of patients or health workers, but that monkeypox could mostly be controlled by isolating contacts and continued epidemiological investigations.

Given the limited global supply of smallpox vaccines, WHO’s emergencies chief Dr. Mike Ryan said the agency would be working with its member countries to potentially develop a centrally controlled stockpile, similar to the ones it has helped manage to distribute during outbreaks of yellow fever, meningitis, and cholera in countries that can’t afford them.

“We’re talking about providing vaccines for a targeted vaccination campaign, for targeted therapeutics,” Ryan said.

“So the volumes don’t necessarily need to be big, but every country may need access to a small amount of vaccine.”

Most monkeypox patients experience only fever, body aches, chills and fatigue.

People with more serious illness may develop a rash and lesions on the face and hands that can spread to other parts of the body.