Vaccinia virus is the live, fully-replicative, orthopoxvirus immunizing agent used to eradicate smallpox. Discovery of vaccinia-variants causing human infection in the Indian subcontinent and in South America (Brazil) has led to the consideration that vaccine may have “escaped” into animal populations; alternatively, these occurrences may be indicative of the origins of vaccinia virus. Vaccinia virus has been genetically engineered and biologically derived into candidate vaccines (some are in clinical trials), with low potential for spread to non-immune contacts.

Vaccination with licensed (fully-replicative) smallpox vaccine is recommended for all laboratory workers at high risk of contracting infection, such as those who directly handle cultures or animals contaminated or infected with vaccinia or other orthopoxviruses that infect humans. It may also be considered for other health care personnel who are at lower risk of infection, such as doctors and nurses whose contact with these viruses is limited to contaminated dressings. WHO does not recommend vaccination in the general public, because the risk of death (1 per 1 000 000 doses) or serious side-effects is greater than the known risk of infection with smallpox.

Vaccination is contraindicated in persons with deficient immune systems, persons with eczema or certain other dermatitis disorders, and pregnant women. Vaccine immune globulin can be obtained for laboratory workers in the USA through the CDC Drug Service (1-404-639-3670), and in other industrialized countries from public health agencies. Vaccination should be repeated unless a major reaction (one that is indurated and erythematous 7 days after vaccination) or “take” has developed. Booster vaccinations are recommended within 10 years in categories for which vaccine is recommended. WHO maintains a supply of the vaccine seed lot (vaccinia virus strain Lister Elstree) at the WHO Collaborating Centre for Smallpox Vaccine at the National Institute of Public Health and Environmental Protection in Bilthoven, The Netherlands. WHO also maintains a stockpile of vaccine should an outbreak occur.