Mpox is a viral disease related to smallpox that is transmitted from animals to humans. Caused by the monkeypox virus, it was first identified in research monkeys in 1958, with the first human case documented in 1970. While many people experience manageable symptoms, the potential for severe outcomes exists.
Understanding Mpox Fatality Rates
The lethality of the mpox virus varies significantly depending on its genetic variant, or clade. Scientists have identified two main clades: Clade I and Clade II. Historically, Clade I, found in the Congo Basin region of Africa, has been associated with more severe disease and a case fatality rate of up to 10%. This clade has disproportionately affected children in the Democratic Republic of Congo (DRC), where they account for a majority of cases and deaths.
In contrast, Clade II, historically found in West Africa, is less severe. This clade is further divided into subclades IIa and IIb, with the Clade IIb variant causing the global outbreak that began in 2022. The fatality rate for Clade II infections is considerably lower, historically estimated at less than 1% to 3.6%. In the United States, the fatality rate for Clade II cases during the recent outbreak was reported to be even lower.
This difference in mortality underscores the role of viral genetics in an infection’s outcome. While Clade I outbreaks have resulted in fatality rates as high as 10%, the Clade IIb strain from the global outbreak has a much lower mortality risk, particularly in regions with accessible healthcare. For instance, from the beginning of 2024, the DRC reported over 6,500 cases and 345 deaths from Clade I, a fatality rate of about 5%, while the global Clade IIb outbreak had a much lower rate.
Factors Influencing Severity and Risk
The risk of developing a severe or fatal case of mpox is not the same for everyone, as specific conditions and demographic factors increase vulnerability. People with compromised immune systems are at a significantly higher risk. This includes individuals with advanced or uncontrolled HIV, who are more susceptible to severe disease and have a higher mortality rate.
Certain life stages also elevate the risk of severe outcomes. Young children, particularly those under eight, and newborn babies can experience more serious illness. Pregnant individuals are another high-risk group, as mpox infection during pregnancy can lead to complications for the fetus, including stillbirth. The location of the outbreak also plays a part, with those in rural villages near tropical rainforests in endemic regions facing higher exposure risk.
When mpox becomes severe, it is due to medical complications that can affect multiple organ systems. The skin lesions can become infected with bacteria, leading to conditions like cellulitis or sepsis, a life-threatening bloodstream infection. The virus can also directly attack vital organs, causing inflammation of the brain (encephalitis), the heart muscle (myocarditis), or the lungs (pneumonia), and eye involvement can lead to potential vision loss.
Distinguishing Symptoms of Severe Infection
The typical presentation of mpox begins with flu-like symptoms such as fever, headache, muscle aches, and swollen lymph nodes. A characteristic rash follows, which progresses from flat spots to fluid-filled blisters and pustules before scabbing over. This rash can appear on the face, palms, soles of the feet, and genital or anal regions. In many cases, symptoms resolve within a few weeks with supportive care.
However, certain signs indicate the illness is progressing to a more dangerous form and require immediate medical attention. An indicator of severity is a very high lesion count, sometimes numbering in the thousands. If these individual sores begin to merge, forming large, confluent patches of affected skin, it suggests a more aggressive infection.
Other red flags are related to complications affecting internal systems and include:
- Difficulty breathing or chest pain, which may signal lung involvement
- Confusion, seizures, or severe headaches, which could point to encephalitis
- Secondary bacterial infections in skin lesions, marked by increasing pain, redness, or pus
- Vision changes or pain in the eyes
- Difficulty swallowing due to sores in the mouth or throat
Medical Interventions and Prevention
The risk of a fatal outcome from mpox is significantly reduced through medical management and preventive measures. For individuals who develop severe disease or are at high risk for it, antiviral medications like tecovirimat (TPOXX) are available. This drug works to stop the virus from spreading within the body and has been shown to be effective in arresting the progression of the disease.
Vaccination is a primary tool for preventing infection and reducing its severity. The JYNNEOS vaccine is approved for individuals at high risk of mpox infection and is administered as a two-dose series. It is considered safe for people with weakened immune systems and can prevent illness or lessen symptoms if a breakthrough infection occurs.
Another vaccine, ACAM2000, is also available but is used less frequently due to a higher risk of side effects. Beyond specific treatments, supportive care is also important. This includes managing pain and fever, ensuring proper hydration and nutrition, and keeping skin lesions clean to prevent secondary bacterial infections.