How Dangerous Is Mpox?
How dangerous mpox is depends critically on which strain (clade) is involved, where someone lives, and their underlying health status. The 2022 global Clade IIb outbreak had a case fatality rate below 0.1% in high-income countries — comparable to seasonal flu. The 2024 Clade I outbreak in Central and East Africa has a much higher fatality rate — up to 10% in some DRC data — particularly affecting children and immunocompromised individuals. The absolute risk of dying from mpox if infected in a high-income country with good healthcare access is very low; the risk in DRC or neighboring countries with Clade I is substantially higher.
| Context | CFR | Notes |
|---|---|---|
| 2022 Clade IIb, high-income countries | <0.1% | Most deaths in advanced HIV or immunocompromised |
| 2022 Clade IIb, overall global | ~0.2–0.3% | Including data from less-resourced countries |
| 2024 Clade Ib, DRC | ~3–10% | Higher in children, malnourished populations |
| Historical Clade I, endemic areas | Up to 10% | Prior to modern supportive care advances |
| Immunocompromised patients (any clade) | Significantly higher | Prolonged, severe, treatment-resistant disease |
- Advanced HIV (CD4 count <200): Highest risk group in 2022 outbreak; extensive, ulcerating lesions; higher mortality
- Other immunosuppression: Organ transplant recipients, cancer patients on chemotherapy
- Infants and young children: In DRC Clade I data, children under 5 years have highest mortality
- Malnourished individuals
- Pregnant women: Higher risk of pregnancy loss and severe neonatal mpox if baby infected at delivery
Severe mpox complications include: Extensive skin lesions covering >50% of body — risk of secondary bacterial infection and sepsis; Ocular mpox — lesions on the cornea can cause permanent vision loss; Proctitis — severe rectal inflammation from lesions in the rectum (experienced by some patients in 2022 outbreak, requiring hospitalisation for pain management); Encephalitis — rare; Pneumonitis — lung inflammation; Myocarditis — heart inflammation; Secondary bacterial sepsis from infected lesions.
- Is mpox as dangerous as smallpox?
- No — mpox is far less dangerous than smallpox. Smallpox (Variola major) had a case fatality rate of approximately 30%; Clade IIb mpox has CFR below 0.1% in high-income settings. Smallpox spread more efficiently (respiratory aerosols) and caused more severe, widespread lesions. The comparison is relevant historically because smallpox vaccines protect against mpox — but the two diseases are very different in severity.
- Can mpox be fatal in healthy young adults?
- Deaths in healthy, immunocompetent young adults from mpox were extremely rare in the 2022 Clade IIb outbreak. The handful of deaths in high-income countries during 2022 were predominantly in people with undiagnosed or advanced HIV. In DRC Clade I areas, healthy young adults do die — the higher CFR is not limited to immunocompromised individuals.
- Does vaccination make mpox less dangerous?
- Yes — JYNNEOS vaccination significantly reduces both the risk of infection and severity of disease if breakthrough infection occurs. Vaccinated individuals who get mpox typically have fewer lesions, shorter illness, and lower hospitalisation rates. Post-exposure vaccination (within 4 days) also reduces severity even if it doesn't fully prevent infection.