What is Smallpox?

Although the World Health Organization (WHO) declared smallpox eradicated in 1980, this contagious and deadly disease remains high on the list of possible bioterror threats.

Unique to humans, the disease is caused by the Variola virus and is transmitted from person to person through direct contact with contaminated fluids and objects, as well as through the air. Smallpox infection is typically associated with an average incubation period of 12 days, followed by fever for two to four days and a subsequent widespread rash. Historically, about 30% of those who became infected with smallpox died from the illness. There is currently no cure for the disease; vaccination is the only proven protection.

While the only known samples of smallpox are held at secure labs in the U.S. and Russia, the U.S. National Research Council found in a 2008 report that "the creation or acquisition of smallpox is well within the technical reach of a determined and well-resourced terrorist."1

Given today's global travel and the virus' long incubation period, all nations must safeguard against this virus. A smallpox outbreak anywhere could quickly become a global, not a local, problem.

History of Smallpox Vaccines


Traditional replicating smallpox vaccines are based on live replicating (reproducing) virus strains which elicit an immune response in the body 10 to 14 days after vaccination. Replicating smallpox vaccines provide protection from smallpox but are associated with rare serious adverse events including severe disability and even death. They are particularly dangerous for individuals who are immune compromised and cannot generate an adequate immune response to control infection by the replicating virus. Replicating vaccines are therefore not recommended for a significant portion of the population, including individuals with HIV, eczema and members of their households.

Individuals who have any of the following conditions are not considered candidates to receive replicating smallpox vaccines:

  • Eczema or atopic dermatitis (even if the condition is not currently active, mild or experienced as a child)
  • Skin conditions such as burns, chickenpox, shingles, impetigo, herpes, severe acne, or psoriasis
  • Immune compromised (e.g. HIV, immunosuppressive therapy)

IMVANEX® is the only licensed smallpox vaccine that cannot replicate in human cells and therefore is not expected to cause the many severe side effects associated with replication. IMVANEX can be given to people who are immunosuppressed and have atopic dermatitis as well as healthy individuals.

1 National Research Council. Department of Homeland Security Bioterrorism Risk Assessment: A Call for Change. Washington, DC: The National Academies Press, 2008

IMVANEX product site version 1. Last updated July 2014.