Mpox may be spreading asymptomatically, greatly increasing its threat, finds new study

Mpox was first detected in the late-1950s, and there have been sporadic outbreaks of the virus in the years since.

The largest outbreak to date began in the summer of 2022, a variant of the virus known as clade II spread through the Western world, including in Britain, the US, and large parts of Europe, mainly between men who have sex with men.

At least 114,000 people have been infected with the variant in the last four years, 220 of which have died.

More recently, a new variant of the virus, clade 1b, emerged in the Democratic Republic of Congo (DRC) in late 2023 after undergoing a rare mutation.

The virus spread rapidly through the war-torn DRC and the exact figures have still not been verified, but it is thought that there were at least 71,000 cases and almost 2,000 deaths – mainly in young children with weakened immune systems from malnutrition and the impact of other diseases like measles and malaria.

The variant has also been detected in several other countries, including Britain, the US, Canada, India, and Thailand, mainly connected to travel from Africa.

Mpox most commonly spreads through physical touch, although it can also spread via respiratory droplets after prolonged face-to-face contact.

Although there is a vaccination available, in the West it is usually only given to men who have sex with men and people travelling to a high-risk area.

In Africa, it is used more widely to contain outbreaks.

The smallpox vaccine – given routinely to children until the early 1970s until it was eradicated – is thought to provide up to 80 per cent protection against mpox because it is from the same family of viruses, the orthopox family.

The new University of Cambridge research may help to explain some of the recent cases of clade 1b mpox that have occurred in Britain and Europe.

In April last year, the UK Health Security Agency (UKHSA) detected a case of Clade Ib mpox in a person in England who had no reported travel history and no known links to previously confirmed cases.

At the time, experts worried that the virus may be transmitting in Britain asymptotically, although there had not yet been enough evidence to understand how exactly it was spreading.

“This study largely reinforces what many of us have long suspected—that mpox exposure and transmission do not always present as classic, clinically obvious disease. Individuals may have asymptomatic or very mildly symptomatic infection, such as a small number of lesions that go unnoticed or are mistaken for something else. If those individuals engage in close physical or sexual contact, transmission could occur unknowingly,” Dr Krutika Kuppalli, associate professor in the division of infectious diseases at the University of Texas Southwestern, told The Telegraph. 

“Understanding that mpox can be mild or go unrecognised is important because it directly shapes how we think about prevention, surveillance, and outbreak control. If we only look for severe or obvious disease, we risk underestimating how widely the virus is circulating and missing opportunities to interrupt transmission,” Dr Kuppalli added. 

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