Poxiviridae

Taxonomic Structure of the Family

Family 00.058. Poxviridae
Subfamily 00.058.1. Chordopoxvirinae
Genus 00.058.1.01. Orthopoxvirus






At least 9 different poxviruses cause disease in humans, but variola virus (VV) and vaccinia are the best known.

VV strains are divided into

-variola major (25-30% fatalities) and
-variola minor (same symptoms but less than 1% death rate)

The precise origins of vaccinia virus are uncertain:

Edward Jenner, 14th May 1796, used cowpox to "vaccinate" 8 year old James Phipps, who he later challenged with VV and showed that he was protected.

For more than 100 years, the "vaccine strains" were propagated from arm-to-arm, but for at least the last 50 years, Vaccinia has been a distinct virus from cowpox.

Vaccination was almost universally adopted worldwide around 1800, but it took a major commitment from the WHO in 1965 to achieve eradication.

Eradication of smallpox was possible for 3 reasons:

1) There is no other reservoir for VV but man (including primates) (c.f. Arboviruses)

2) VV causes only acute infections, from which the infected person either:
a) dies
b) recovers with life-long immunity (c.f. Herpesviruses)

3) Vaccinia virus is an effective immunogen.



Infection with both viruses occurs naturally by the respiratory route and is systemic, producing a variety of symptoms, but most notably with VV characteristic pustules and scarring of the skin. Replication of vaccinia is more localized. Administration of vaccinia to immunocompromised hosts results in systemic infection with neurological damage or death. The vaccine is contraindicated in:

• Eczema, atopic dermatitis or other acute, chronic, or exfoliative skin conditions
• Diseases or treatments which cause immunodeficiency or immunosuppression
• Moderate or severe acute illnesses
• Previous allergic reaction to smallpox vaccine or any of the vaccine components
• Pregnancy
• Breastfeeding mothers


• Infants and children under 12 months of age