(CNN) More cases of a rare disease have been reported worldwide, including in the United States -- where one health official said he expects new cases in the days ahead.
Confirmed cases have been identified in Australia, Belgium, Canada, France, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, the United Kingdom and the United States -- which had between one and five confirmed monkeypox cases as of Saturday, the WHO said.
"The situation is evolving and WHO expects there will be more cases of monkeypox identified as surveillance expands in non-endemic countries," the news release said.
Dr. Ashish Jha, the White House Covid-19 response coordinator, told ABC he wouldn't be surprised if the US saw "a few more" cases of monkeypox in the coming days.
"But I feel like this is a virus we understand, we have vaccines against it, we have treatments against it, and it's spread very differently than SARS-CoV-2" -- the virus that causes Covid-19, Jha told ABC's Martha Raddatz on Sunday.
"It's not as contagious as Covid. So I am confident we're going to be able to keep our arms around it," Jha said. "But we'll track it very closely and use the tools we have to make sure we can continue to prevent further spread and take care of the people who get infected."
Health experts say close contact with an infected person is required to spread the monkeypox virus.
Infection can develop after exposure to "broken skin, mucous membranes, respiratory droplets, infected body fluids or even contact with contaminated linen," according to Neil Mabbott, personal chair in immunopathology at the veterinary school of the University of Edinburgh in Scotland.
Though experts say monkeypox is not as contagious as Covid-19, President Joe Biden said everyone should be concerned about the spread of monkeypox -- even as scientists work to learn more about the recent spread.
"They haven't told me the level of exposure yet, but it is something that everybody should be concerned about," Biden told CNN's Kaitlan Collins as he was departing South Korea on Sunday.
"We're working on it hard to figure out what we do and what vaccine, if any, might be available for it," Biden said. "It is a concern in that if it were to spread it would be consequential. That's all they told me."
CNN previously reported that the US Centers for Disease Control and Prevention is evaluating whether a smallpox vaccine should be offered to health care workers treating monkeypox patients and other people who may be at "high risk" for exposure to monkeypox.
The variola virus that causes smallpox and the monkeypox virus are somewhat related, as they are both members of the Orthopoxvirus genus -- belonging to the scientific family of "pox" viruses. Therefore, some of the same vaccines given to prevent smallpox have also been shown to prevent monkeypox.
Initial monkeypox symptoms are typically flu-like, such as fever, chills, exhaustion, headache and muscle weakness.
"A feature that distinguishes infection with monkeypox from that of smallpox is the development of swollen lymph nodes," the CDC said.
After that, a widespread rash typically appears on the face and body -- including inside the mouth, on the palms of the hands and soles of the feet.
The painful, raised poxes are pearly and fluid-filled, often surrounded by red circles. The lesions finally scab over and resolve over a period of two to three weeks, the CDC said.
Historically, cases of monkeypox have typically been reported from West Africa or Central Africa, said Jennifer McQuiston, deputy director of the Division of High Consequence Pathogens and Pathology within the CDC's National Center for Emerging and Zoonotic Infectious Diseases.
"We have a level of scientific concern about what we're seeing because this is a very unusual situation," McQuiston told CNN on Thursday.
"We don't see it in the United States or in Europe -- and the number of cases that are being reported is definitely outside the level of normal for what we would see," McQuiston said.
A top UK health official told the BBC on Sunday that people should be aware of monkeypox -- but that the risk to the general population "remains extremely low at the moment."
"I think people need to be alert to it," said Susan Hopkins, chief medical adviser for the UK Health Security Agency.
"We really want clinicians to be alert to it and send the test if they're concerned."
Hopkins said based on reports from Africa, the UKHSA knows certain people are "much more at risk of severe disease, particularly immunosuppressed individuals or young children."
While there is "no direct vaccine for monkeypox," Hopkins said, "we are using a form of smallpox vaccine or third-generation smallpox vaccine that's safe on individuals who are contacts of cases."