Monkeypox infection after they shared a flight with a British patient who tested positive for the virus.

The individuals sat within a three-row radius of the Brit on a nearly seven-hour flight from Nigeria to the UK on May 4. He later became the country’s first confirmed case.

Dr Jennifer McQuiston, a senior official at the Centers for Disease Control and Prevention (CDC), told STAT News the U.S. patients would be monitored for 21 days.

A total of 12 cases have been confirmed in Europe so far in the global outbreak, with 24 people being probed for the virus across the UK, Portugal and Spain.

Infections are more common in central and west Africa, where they generally result from direct contact with infected animals.

But the virus can also be spread via direct contact with infectious lesions in the skin, or from the coughs and sneezes of someone with a monkeypox rash.

Up to one in 10 cases are fatal, but the strain spreading globally is milder and thought to have a fatality rate of about one in 100 — similar to Covid’s at the start of the pandemic.

McQuiston warned the CDC is considering issuing another health alert — similar to that for the hepatitis outbreak — for medical professionals.

She added that a number of cases in the UK appear to be linked to sexual transmission among gay and bisexual men, likely due to contact with infectious lesions in the skin.

‘There’s a lot of travel between the U.K. and the United States and other global area,’ she said.