Public Health Briefing: mpox

This was previously most common in the Congo Basin area. Two subtypes are currently causing disease:

• Clade 1a, currently causing disease in the Eastern Democratic Republic of Congo (DRC) and neighbouring countries, mostly among adults, spreading predominantly through sexual contact
• Clade 1b, which is believed to be contributing to the current rise in mpox cases in East, West and Central Africa. This is mostly affecting children and spreading by multiple modes.

Wild mammals in east, west and central Africa may have mpox. Touching, being bitten by, or eating an undercooked infected animal can cause infection.

Scabs from a person with mpox contain infectious virus, and contact with the scabs can spread the infection, mostly by: caring for an infected person; kissing, touching, or having sex with an infected person; an infected person coughing or sneezing on you. Catching mpox from being coughed or sneezed on is possible, but not common: it can happen to a person caring for, or sharing a hospital room with, an infected person. This is not significant in the current rise in cases.

Shed scabs are still infectious, so handling the bedsheets of a person who is infected can cause person to person infection.

After infection, it takes 5-21 days for symptoms to emerge. People are considered to be infectious from the day they first show symptoms, until the day their last scab falls off.

Usually, the virus first causes flu-like symptoms including fever. After several days of flu-like symptoms, a rash develops and spreads across the body. The rash turns into lesions, which eventually scab and fall off. The scabs can cause scarring.

Most people recover from mpox after 2-3 weeks. However, pregnant women, people who are immunocompromised, and children are more likely to develop complications or severe disease. People can die from the disease, especially if they are in these groups, and have limited access to healthcare.

Death rates have been estimated for the different clades, but their accuracy when considering implications of the disease in the UK is limited. This is because most of the data on death rate comes from cases in Africa, which occur in different circumstances, in different demographics, and with different healthcare options. The estimates themselves have limited accuracy because of variable reporting of cases. Therefore, they are not included in this article.

Numbers  of mpox cases in west, east, and central Africa have increased sharply, and cases have spread to new areas. This caused the Africa Centre for Disease Control (CDC) to declare a Public Health Emergency of Continental Security (PHECS), and the World Health Organisation (WHO) to declare a Public Health Emergency of International Concern. These declarations release additional funding and allow relevant actions to be taken in certain countries. These declarations also call international attention to the situation, rather than indicating that the immediate threat is global in scale.

The WHO had previously declared a global public health emergency for mpox in 2022, when case numbers increased on multiple continents. The emergency was ended in May 2023 when case numbers fell again. 

Africa CDC issued this statement on 13 August 2024, reported in the journal Nature on 23 August 2024:

’Mpox was declared a PHECS in part to unlock access to emergency resources, including funding, personnel and technical support, but the mpox outbreaks in Africa are a global concern, with the potential for international spread.’ 

• Prof Nicaise Ndembi, Editor-in-Chief, Africa CDC

Dr Tedros Adhanom Ghebreyesus, WHO Director General, issued this statement on 14 August 2024

The emergence of a new clade of mpox, its rapid spread in eastern DRC, and the reporting of cases in several neighbouring countries are very worrying. On top of outbreaks of other mpox clades in DRC and other countries in Africa, it’s clear that a coordinated international response is needed to stop these outbreaks and save lives.

In July 2024, Burundi, Kenya, Rwanda, and Uganda all reported mpox cases for the first time. Currently (September 2024) in the DRC, cases are being reported at far higher rates than normal, and in new regions. Most of these cases are occurring to children, while far lower levels continue to occur in adults.

Before 2022, the disease also mostly infected children in west Africa, but in far smaller numbers, and was mostly transmitted to them by animals.

Several factors may be causing more children to become infected, and in new regions: 

• Political unrest and climate change in the regions affected by mpox has impacted children. Many children have been displaced and are living in refugee camps. The displacement has spread the disease to new areas. The close quarters and unsanitary conditions in refugee camps allow the disease to spread more easily within them. Children who are malnourished, which is common in people who have been displaced, also appear to be more likely to catch mpox. 
• Children’s immune systems do not protect them from mpox as well as adults. In addition, people born in the 1970s or earlier received smallpox vaccines, which provide some protection from mpox. The vaccination programme ended when smallpox was eradicated, so young people have not had these types of vaccine.
• The 1b clade which is causing most of the new infections in children may be better at passing from human to human than other clades. This has yet to be confirmed. 

For adults within Africa, detailed transmission information is not available. Displacement, malnutrition, and exposure to infected animals could all also contribute to the number adult cases currently occurring within Africa, alongside sexual contact. Sexual contact is linked to 95% of the adult cases outside Africa. However, the current spike in infections seems to be primarily affecting children, for the reasons described above.

The fact that adult cases have not spiked as significantly suggests that the geopolitical factors in play are more significant than the possibility that clade 1b is more infectious.

Many sources discussing mpox use data starting from the beginning of the 2022 spike in cases. This means they often include statistics about thousands of cases in the UK, Europe, and north and south America, almost all of which occurred in 2022. In the two years between 2022 and 2024, cases have remained stable and low in most countries outside west, east, and central Africa. In the UK, according to government data, fewer than 50 cases of confirmed or highly probable mpox were recorded per month between January 2023 and August 2024. There have been no confirmed cases of mpox in the UK caused by the clade 1b type.

We are likely to see some more mpox cases in the UK, because when there are a lot of cases in one place, some generally spread elsewhere by global travel. This is already playing out in government data, with more cases being detected here in the last two months than any of the previous months since 2022. The numbers are still low, and don’t suggest a bigger surge is coming.

The conditions which are causing the surge of cases in Africa – malnutrition and displacement – are not present in the UK. So while we should be prepared for sporadic cases of mpox, it is unlikely we will see it spread in the UK in the same way. All the cases in the UK to date have been the milder clade 2 type, and the majority have been in adult men, likely through sexual contact.

In countries outside Africa, the main way mpox is spread is through sexual contact, particularly between men who have sex with other men. Men aged 18-44 have made up 79.4% of cases recorded outside Africa. In the UK, men who have sex with other men, particularly with new partners, are at the greatest risk of catching mpox.

While it is possible to catch mpox from an infected person coughing or sneezing near you, the infected person will probably at that stage feel and look very sick. The people at risk of catching mpox this way are people directly caring for a sick person. There is no evidence at this stage that we should worry about mpox readily transmitting through coughs, or that measures like masks or distancing would be needed for the general public if cases here did rise.

The NHS has detailed guidance on mpox and what to do if you think you have it. Mpox is rare in the UK. However, you can further reduce your risk of contracting mpox by:

• Washing your hands regularly with soap and water or alcohol hand sanitiser
• Looking for possible symptoms of mpox for 3 weeks after returning from west, central or east Africa
• Talking to sexual partners about their sexual health
• Being aware of the symptoms of mpox if you are sexually active, especially with new partners
• If you have mpox symptoms, take a break from sex and intimate contact until you’ve seen a doctor
• Do not go near wild animals, or eat their meat, while travelling in west, central or east Africa
• Do not share bedding or towels with people who may have mpox
• Do not have close contact (within a metre) of people who have mpox.

Mpox and chickenpox can look similar. Generally, mpox is more likely to come with swollen lymph nodes, fever before the lesions develop, and slower development of lesions than chickenpox. The lesions themselves are generally painful in mpox, until they begin to scab, whereas chickenpox lesions are itchy. These are typical differences between the diseases, but not fully reliable, hence the need for a healthcare professional to confirm. In the UK, whether you suspect you or someone you care for has chickenpox or mpox, consult a doctor.

The new clade 1b variant may be spreading more readily between people than previous variants. This could be due to the circumstances in which people are getting infected, or it could be evidence that the virus is adapting to become better at spreading from person to person. It is also possible that some infected people could infect others before they develop symptoms, or without developing symptoms. More research is needed on these aspects of mpox and their potential implications. At this stage, no additional precautions need to be taken in the UK because of these possibilities.

The situation in the affected parts of Africa is extremely serious. We in the UK should do what we can to support efforts to contain and treat the cases there. As well as helping the people directly affected, providing resources to stop the spread of the virus reduces the chances of new variants of the disease emerging. New variants might become more infectious or more deadly, and increase the risk the disease poses to everyone. The changes in who is contracting mpox, where, and how could mean the disease is changing, and that is concerning. The declaration of an emergency by the WHO should help direct more resources to combatting mpox.

We should always be concerned about new diseases spreading. We should always take whatever precautions we can to stop this.

Mpox, NHS, (last reviewed October 2022)

Mpox (monkeypox) outbreak: epidemiological overview, 5 September 2024, Research and analysis, UK Government, 5th September 2024

Growing mpox outbreak prompts WHO to declare global health emergency, Nature, 13th August 2024

Mpox is a public health emergency - what happens now?, Nature, 21st August 2024

Multi-country outbreak of mpox, External situation report #35, World Health Organisation, 12th August 2024

Americo, J.L., Earl, P.L. and Moss, B., 2023. Virulence differences of mpox (monkeypox) virus clades I, IIa, and IIb. 1 in a small animal model. Proceedings of the National Academy of Sciences, 120(8), p.e2220415120.

Saied, A.A., 2023. Mpox virus Clade IIb detection in the air. Journal of Medical Virology, 95(5), p.e28775.

Gao, L., Shi, Q., Dong, X., Wang, M., Liu, Z. and Li, Z., 2023. Mpox, Caused by the MPXV of the Clade IIb lineage, goes global. Tropical Medicine and Infectious Disease, 8(2), p.76.