CDC is updating webpages with the term "mpox" to reduce stigma and other issues associated with prior terminology. This change is aligned with the recent World Health Organization decision.

About Mpox

What is Mpox?

Mpox is a rare disease caused by infection with the mpox virus. Mpox virus is part of the same family of viruses as variola virus, the virus that causes smallpox. Mpox symptoms are similar to smallpox symptoms, but milder, and mpox is rarely fatal. Mpox is not related to chickenpox.

Mpox was discovered in 1958 when two outbreaks of a pox-like disease occurred in colonies of monkeys kept for research. Despite being named “monkeypox,” the source of the disease remains unknown. However, African rodents and non-human primates (like monkeys) might harbor the virus and infect people.

The first human case of mpox was recorded in 1970. Prior to the 2022 outbreak, mpox had been reported in people in several central and western African countries. Previously, almost all mpox cases in people outside of Africa were linked to international travel to countries where the disease commonly occurs or through imported animals. These cases occurred on multiple continents.

There are two types of mpox virus: Clade I and Clade II. Infections in the current outbreak are from Clade II, or more specifically, Clade IIb.

Infections with Clade IIb are rarely fatal. Over 99% of people who get this form of the disease are likely to survive. However, people with severely weakened immune systems, children under 1 year of age, people with a history of eczema, and people who are pregnant or breastfeeding may be more likely to get seriously ill or die.

The Clade I type of mpox virus has a fatality rate around 10%.

2022 Mpox Outbreak

Science at CDC

Scientific evidence and studies behind mpox guidance and recommendations.

Science Behind Transmission

Multi-National Technical Reports