How worried should we be about the new mpox strain?

Health authorities have announced the first case of Clade1b mpox has been identified in the UK.

Since January 2024, there have been around 1,000 deaths out of 33,000 suspected cases in the Democratic Republic of Congo, according to the Centre for Disease Control.

So far sustained transmission has only been seen in DRC and other African countries. Considering the 2022-23 outbreak of Clade 2b, how worried should the public be about this new case?

Mpox, formerly known as monkeypox, is a viral infection that spreads through close person to person contact.

There are different strains of the virus, but the two major ones are Clade 1 and Clade 2.

Clade 2 has been in the UK since 2022 and led to the major outbreak in 2022-23, whereas Clade 1 previously was only reported in five countries in central Africa.

Anyone can catch the virus through close contact with someone who has it, or through contact with contaminated materials, such as bedsheets or towels, and contact with infected animals.

Clade 1b mpox first emerged in the Democratic Republic of Congo (DRC) just over a year ago.

A second variant, Clade1a, is also circulating in the DRC and predominately affects children, while Clade1b is spreading mostly between adults through intimate and sexual contact.

According to experts Prof Azra Ghani, Director, MRC Centre for Global Infectious Disease Analysis, and Dr Lilith Whittles, Lecturer, MRC Centre for Global Infectious Disease Analysis, both Imperial College London, the severity of the current Clade 1b remains unclear. 

They said: “Severity likely depends on age, underlying co-morbidities such as immunocompromising conditions, and availability of supportive healthcare.”

In August the World Health Organisation (WHO) declared a public health emergency of international concern because of the rapid spread of the strain after its emergence in the Democratic Republic of the Congo (DRC) last year.

Currently, the virus has primarily impacted African countries however cases are beginning to be reported in Europe globally, in Sweden, Germany, India and now the UK.

The case in Sweden and the UK have been reported to have been people who had travelled to countries in Africa where there had been reported cases in the community.

The European Centre for Disease Control has stated more imported cases are likely to occur, so the case identified in the UK this week is not unexpected.

The case in the UK was detected through a PCR test, the UK Health Security Agency has confirmed.

According to Professor Paul Hunter, Professor in Medicine, UEA, it is difficult to distinguish between the Clade2b, which has been circulating since 2022, and Clade1b.

He said: “Not all such infections will be diagnosed, particularly in people who were previously vaccinated due to being at risk of clade 2b.  Even when diagnosed it is very difficult to distinguish the two clades other than by gene sequencing which may not always be done in all European countries.”

Overall, UK and EU authorities have said the risk for the general public is low.

Dr Hunter said: “It is likely that if mpox clade 1b does spread in Europe, it would spread predominantly in the same sexual networks that clade 2b spreads in.”

He added: “It is unlikely that we will see a similar epidemic with clade 1b as we saw with clade 2b.  The reason for this is that vaccine given for 2b is also effective against 1b and people who have had an infection with 2b will also have reasonable protection against 1b, though not 100%.

There are two vaccines approved against mpox, MVA-BN and LC16. These jabs are based on weakened versions of orthopoxviral and were developed for smallpox.

Dr Albarnaz warned: “Availability of these vaccines is very limited, representing a major bottleneck for the control strategies.”

However, Prof Azra Ghani, Director, MRC Centre for Global Infectious Disease Analysis, and Dr Lilith Whittles, Lecturer, MRC Centre for Global Infectious Disease Analysis argued the previous effectiveness of the vaccination against Clade2b, the strain circulating in 2022-23 suggests “it highly likely that current vaccines will offer strong protection.”