What Is Mpox?

Mpox (formerly monkeypox) is a viral disease caused by Monkeypox virus, an orthopoxvirus related to smallpox. It produces a characteristic rash of fluid-filled blisters that progress over 2–4 weeks, accompanied by fever, swollen lymph nodes, and muscle aches. First identified in humans in 1970 in the DRC, mpox remained a regional concern until 2022 when it spread to 110+ countries in the largest outbreak outside Africa ever recorded. In 2024 a new Clade I variant in Central and East Africa was declared a Public Health Emergency of International Concern (PHEIC) — the second mpox PHEIC in two years.

Mpox spreads through:

Direct skin-to-skin contact with the rash, lesions, or scabs of an infected person — the dominant route in the 2022 global outbreak
Close respiratory contact during prolonged face-to-face interaction (not aerosol/airborne)
Contaminated materials: sharing bedding, towels, clothing with an infected person
Animal-to-human: Contact with infected rodents or primates in Central African endemic areas

Mpox is contagious from symptom onset until all scabs have fallen off — typically 2–4 weeks. There is no documented pre-symptomatic transmission.

Incubation: 3–17 days. Typical presentation:

Fever, headache, muscle aches, back pain, swollen lymph nodes (a distinguishing feature vs chickenpox)
Rash appearing 1–5 days after fever, starting on face or site of exposure, spreading to trunk and limbs; may involve palms, soles, mouth, genitals
Lesion progression: macule (flat) → papule (raised) → vesicle (fluid-filled) → pustule → scab → healing (2–4 weeks total)

Clade I mpox (DRC, 2024) tends to be more severe with higher fatality rates (up to 10%) vs Clade IIb (2022, <0.1% in high-income settings).

JYNNEOS (Imvamune/Imvanex) — a 2-dose modified vaccinia Ankara vaccine — is approved for mpox prevention and post-exposure prophylaxis. It can be given within 4 days of exposure for best protection, up to 14 days for partial protection. Old smallpox vaccines (ACAM2000) provide ~85% cross-protection. Tecovirimat (TPOXX) is an antiviral available under compassionate use/expanded access for severe disease in immunocompromised patients, children, and pregnant women.

Is mpox the same as chickenpox?: No. Mpox (Monkeypox virus, an Orthopoxvirus) and chickenpox (Varicella-zoster virus, a Herpesvirus) are caused by completely different viruses from different families. Both cause rashes, but mpox characteristically causes swollen lymph nodes and a more uniform rash progression. Prior chickenpox infection or vaccination provides no protection against mpox.
Who is at risk for mpox in 2025?: Risk is context-dependent. In countries that experienced the 2022 Clade IIb outbreak: unvaccinated people with multiple sexual partners remain at elevated risk. In DRC and neighboring East African countries: Clade I transmission affects all demographics including children, through household contact and healthcare exposure. Global travelers to affected regions should monitor WHO travel advisories.
How long is someone contagious with mpox?: From symptom onset until all scabs have completely fallen off — typically 2–4 weeks. Isolation must continue for this full period. The dried scabs are themselves infectious. Unlike many respiratory diseases, mpox does not spread from people who have no symptoms.