Mpox, a viral disease caused by a virus related to smallpox, has raised public health concerns following its global spread. First identified in humans in 1970 in the Democratic Republic of the Congo, the virus was historically confined to parts of West and Central Africa. Recent outbreaks, however, have demonstrated its capacity to spread between people in non-endemic regions, prompting questions about its severity.
Understanding Monkeypox Mortality Rates
The deadliness of mpox is not uniform; it depends significantly on the specific viral strain, known as a clade. Scientists primarily recognize two main types: Clade I, historically found in Central Africa, and Clade II, which is endemic to West Africa. The assessment of this risk is often expressed as a case fatality rate (CFR), which measures the proportion of deaths among confirmed cases of a disease.
Historically, Clade I has been associated with more severe disease and a higher CFR, which has been estimated to be as high as 10%. In contrast, Clade II has a much lower historical CFR, between 1% and 3.6%. Most cases in the 2022-2023 global outbreak were caused by a subtype of Clade II, known as Clade IIb.
The Clade IIb virus responsible for the recent worldwide spread has a significantly lower fatality rate, with more than 99% of people surviving. While historical data from Africa showed higher death rates, particularly in children and those without access to quality healthcare, the CFR during the 2022 global outbreak was much lower, at approximately 0.2%.
Populations at Higher Risk for Severe Disease
Certain groups of people are more susceptible to experiencing a severe or complicated mpox infection. People with compromised immune systems, such as those with untreated HIV, undergoing cancer chemotherapy, or taking immunosuppressant drugs for organ transplants, are at a heightened risk for severe outcomes.
Children, particularly those under the age of eight, represent another vulnerable population. Their immune systems are not yet fully developed, which can make it more difficult for their bodies to mount an effective defense against the virus. Historical data from Africa indicates that malnourishment can further compound this risk in children. Similarly, individuals who are pregnant face a greater likelihood of severe disease, which can also pose risks to the fetus.
A pre-existing skin condition, such as eczema or atopic dermatitis, can also increase the risk of a more severe mpox illness. The virus causes a characteristic rash with lesions, and those with compromised skin integrity may experience more widespread and severe skin symptoms.
How Monkeypox Can Become Fatal
Death from mpox is not a direct result of the virus itself but from the severe complications that can arise. A common pathway to a fatal outcome is sepsis, a life-threatening condition where the body’s response to an infection becomes dysregulated, triggering widespread inflammation that can lead to tissue damage, organ failure, and shock.
Another serious complication is encephalitis, which is inflammation of the brain. This can occur if the virus infects the central nervous system, leading to neurological symptoms such as confusion, seizures, and loss of consciousness. Brain inflammation can cause permanent neurological damage or death.
The skin lesions that characterize mpox can also become a source of fatal complications. If the blisters and sores are not kept clean, they can become infected with bacteria. These secondary bacterial infections can spread from the skin into the bloodstream or deeper tissues, leading to conditions like cellulitis or sepsis. The virus can also directly infect the lungs, causing severe pneumonia or bronchopneumonia, which impairs breathing and can be fatal, especially in individuals with weakened immune systems.
Role of Vaccines and Antivirals
Medical countermeasures are available to prevent and treat mpox, reducing the risk of severe disease and death. Vaccination is a primary tool for prevention, and the JYNNEOS vaccine is the main one used. It is approved for both smallpox and mpox and can be administered before exposure (pre-exposure prophylaxis, or PrEP) to people at high risk of infection.
The vaccine can also be given after a known or suspected exposure to the virus (post-exposure prophylaxis, or PEP). When given within a few days of exposure, vaccination can prevent the disease from developing or make it significantly less severe.
For individuals who are already sick with mpox, the antiviral medication tecovirimat (TPOXX) can be used to treat the infection. This medication works by inhibiting a viral protein, thereby preventing the virus from spreading within the body. Tecovirimat can lessen the severity and duration of the illness and may be particularly helpful for people who are at high risk for severe disease or who have developed complications.