In a document published Friday, the U.K. Health Security Agency (UKHSA) advised people who have had close contact with an infected person to self-isolate for 21 days.

No one in the U.K. with a confirmed or potential case of monkeypox is required to self-isolate by law.  

According to the UKHSA, “high risk” exposure to the virus could occur via contact with a patient’s broken skin, mouth, nose or bodily fluids, but it could also happen through contact with contaminated clothes or bedding.

High risk contacts include sexual partners, people who live in the same house, or anyone who comes into contact with an infected person’s bodily fluids, for example via a cough or sneeze, officials said.

As well as isolating for 21 days, people who have had this level of exposure to monkeypox are being told to avoid contact with immunosuppressed people, pregnant women, and children under 12 where possible.

They should also be offered a smallpox vaccine, ideally within four days but up to a maximum of 14 days after exposure, the health body said.

To date, the U.K. has confirmed 20 cases of monkeypox, with health officials expected to announce more confirmed cases on Monday.

World’s first compulsory monkeypox quarantine

Elsewhere, Belgium became the first country in the world to implement a compulsory 21-day quarantine for confirmed monkeypox patients on Friday.

High-risk contacts of monkeypox cases in Belgium would not be required to isolate, according to local media, but their condition would be monitored.

Belgium confirmed its first three monkeypox cases on Friday, with the three patients linked to the Darklands fetish festival, which took place between May 4 and May 9 in the Belgian city of Antwerp.

“There’s reason to assume that the virus has been brought in by visitors from abroad to the festival after recent cases in other countries,” the festival’s organizers said in a statement on Friday.

“The Risk Assessment Group of the federal government has asked Darklands to inform its guests about these infections.”

Cases ticking up globally

Monkeypox has an incubation period that can range from 5 to 21 days, according to the WHO.

The virus, which can cause symptoms including fever, headaches and swollen glands, causes a rash that starts as raised spots which blister and fall off.

Most countries have said people with confirmed cases of monkeypox should isolate for 21 days, with the U.S. CDC advising monkeypox patients to isolate until all crusts from the rash are gone.

As of May 21, 92 confirmed cases and 28 suspected cases of monkeypox have been reported to the WHO from 12 countries, including the U.S., Australia and Germany.

Portugal, Spain and the U.K. have the highest number of confirmed cases so far, each having reported between 21 and 30 confirmed cases to the WHO.

No fatalities from the virus have been reported.

Speaking in Geneva on Sunday, WHO Director General Tedros Adhanom Ghebreyesus said the world was facing multiple public health crises on top of the COVID-19 pandemic.

“We face a formidable convergence of disease, drought, famine and war, fueled by climate change, inequity and geopolitical rivalry,” he said.

Health authorities in the U.K. and France have said the disease is usually “a mild self-limiting illness,” with patients generally making a full recovery within a few weeks.

There are two strains of the virus. The milder West African strain, which is the variant currently circulating in Europe and North America, has a recorded fatality rate of around 1%, experts told Fortune last week.