Mpox: What to know about the most recent strain, clade 1b

Mpox is a highly contagious viral disease similar to the now-eradicated smallpox, but less severe. It is a zoonotic infection, meaning that it can spread from animals to humans. It can also spread from person to person.

Formerly known as monkeypox, mpox is largely found in west and central Africa, but it also began spreading in Europe and North America in 2022, leading to the World Health Organisation (WHO) declaring it a public health emergency from July 2022 to May 2023. 

There are two main types of mpox - clade 1 and clade 2.  A clade is a broad grouping of viruses that has evolved over decades that has distinct genetic and clinical differences.

Clade 1: causes more severe illness and deaths. Some outbreaks have killed up to 10 per cent of the people who get sick, although more recent outbreaks have had lower death rates. Clade 1 is endemic to Central Africa. However, now a more worrying strain of mpox called clade 1b has been identified, which is of particular concern due to its higher transmissibility and more severe clinical outcomes. 

Clade 2: was responsible for the global outbreak in 2022. Infections from clade 2 mpox are less severe. More than 99.9 per cent of people survive. Clade 2 is endemic to West Africa.

The spread of the new variant, clade 1b, and its high fatality rate in parts of Africa, has sparked concern among scientists, and led the World Health Organisation (WHO) to declare it a public health emergency of international concern. This new strain is thought to be more deadly than previous ones - with four in 100 cases leading to death. 

Two people travelling to Africa, one from Sweden and one from Thailand, have become infected with clade 1b and brought it back to their countries. As a result, experts around the world are continuing to monitor the situation closely, and WHO is actively supporting containment efforts.

Mpox can be severe in children, pregnant women or people whose immune systems are compromised due to illness or specific treatments. 

The symptoms of mpox are similar to but milder than the symptoms of smallpox, with the main difference being that it causes lymph nodes to swell while smallpox does not.

The defining symptom of mpox is a distinctive itchy rash that later turns to blisters. The rash, which can be very itchy or painful, changes and goes through a number of different stages before finally forming a scab, which later falls off. The lesions can cause scarring.

The rash, often beginning on the face, spreads to other parts of the body, mainly the palms of the hands and soles of the feet. It usually appears two to four days after the other symptoms. 

The early signs of mpox include flu-like symptoms such as:

• Fever 
• Chills
• Headaches
• Backache
• Muscle aches
• Fatigue
• Swollen lymph nodes

The incubation period (time from infection to symptoms) for mpox is usually 7−14 days but can range from 5−21 days.

The UN health agency recommends several vaccines for use against mpox. Many years of research have led to the development of newer and safer vaccines for smallpox, which may also be useful for mpox. 

Only people who are at risk of exposure to mpox are being considered for vaccination, and mass vaccination is not being recommended at this time. Travellers who may be at risk based on an individual risk assessment with their healthcare provider, may wish to consider vaccination. 

Symptoms normally resolve on their own without the need for treatment and most people fully recover in two to four weeks. If needed, medication for pain and fever can be used to relieve some symptoms.  It is important for anyone with mpox to stay hydrated, eat well, and get enough sleep. 

Anti-viral drugs used to treat smallpox can be used to treat anyone who becomes severely ill with mpox. People who suspect they have mpox should isolate and seek medical care.