New Mpox strain Clade 1b ‘most dangerous so far’ and ‘could spread internationally’, scientists warn

Scientists tracking the spread of a dangerous new strain of the Mpox virus have said it is time to “get prepared”.

Researchers in the Democratic Republic of Congo (DRC) are warning it could spread internationally – with potentially more severe symptoms and higher mortality.

Known as Clade 1b, the strain first emerged in September among sex workers in the DRC mining town of Kamituga, around 170 miles (273km) from the border with Rwanda.

There have now been around 1,000 confirmed cases in the country’s South Kivu province.

On Monday, the first cases were confirmed in the city of Goma, which is also close to the Rwanda border.

Estimates of the strain’s severity are inexact, as only cases among patients who have gone to hospital have been studied.

However, early estimates suggest it has a mortality rate of 5% for adults and 10% for children.

“It is undoubtedly the most dangerous so far of all the known strains of Mpox,” said Jean Claude Udahemuka, from the University of Rwanda.

“Everyone should get prepared and support the local response,” he added.

It comes as South Africa recorded a third Mpox death on Tuesday. Previous deaths there have been due to an ongoing outbreak of the earlier Clade 2 strain.

Genetic sequencing will confirm whether they might have been due to the new strain, but so far it has not been confirmed outside of DRC.

In 2022, the Clade 2 strain of Mpox (previously known as Monkeypox) caused a global outbreak – largely among gay and bisexual men.

More than 97,000 cases have been recorded internationally, including nearly 4,000 in the UK. Most cases are mild and the mortality rate is less than 0.5%.

Vaccination with a smallpox vaccine, which gives protection against Mpox, as well as public health campaigns, have helped control Clade 2.

Like Clade 2, Clade 1b causes a severe blister-like rash at the site of the infection.

But symptoms are more severe, with the rash often spreading to the entire body, according to Leandre Murhula Masirika, a research co-ordinator in South Kivu province.

‘We are very afraid’

Most new cases in the DRC are sexually transmitted, but the new strain can spread more readily from person to person – with infections reportedly jumping between household members and at least one outbreak recorded among schoolchildren.

It has also caused miscarriage in women, with early evidence suggesting long-term health problems in some people who have recovered from infection.

“We are very afraid [Clade 1b] is going to cause more damage in terms of health importance,” said Murhula Masirika.

Read more:
Monkeypox given new name by WHO
UK launches research hub to tackle Monkeypox

The World Health Organization and other global health bodies have plans for an emergency vaccination campaign in South Kivu.

It is hoped the recent end of the rainy season in the region will improve access to affected areas, particularly the outbreak’s epicentre of Kamituga.

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However, there is an urgent need to better understand the new strain, according to Trudie Lang, professor of global health research at the University of Oxford.

This is particularly true when it comes to its incubation period and whether it can spread without symptoms – key factors which determine the severity of an epidemic.

“We can see the escalation of cases, but these are reported cases in hospitals – this is the most worrying piece when it comes to the unknowns we have,” said Professor Lang.