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These revised recommendations on vaccinia [smallpox] vaccine update the previous recommendations [MMWR 1985;34:341-2] and include current information on its use among laboratory and health-care workers occupationally exposed to vaccinia, recombinant vaccinia viruses, and other orthopoxviruses that can infect humans. This report also contains revised recommendations on revaccination of high-risk workers and information on contraindications to vaccination.
INTRODUCTION
Vaccinia [smallpox] vaccine is a highly effective immunizing agent that brought about the global eradication of smallpox. The last naturally occurring case of smallpox occurred in Somalia in 1977. In May 1980, the World Health Assembly certified that the world was free of naturally occurring smallpox [1].
Because of vaccination programs and quarantine regulations, the risk of importation of smallpox into the United States was reduced by the 1960s. As a result, routine vaccinia vaccination was discontinued in 1971 [2]. In 1976, the recommendation for routine vaccination of health-care workers was also discontinued [3]. In 1982, the only active licensed producer of vaccinia vaccine in the United States discontinued production for general use, and in 1983, distribution to the civilian population was discontinued [4]. For several years all military personnel continued to be routinely vaccinated. However, only selected groups of military personnel are currently vaccinated against smallpox.
Since January 1982, smallpox vaccination has not been required for international travelers, and International Certificates of Vaccination no longer include smallpox vaccination [5].
In 1980, the Immunization Practices Advisory Committee [ACIP] recommended the use of vaccinia vaccine to protect laboratory workers from possible infection while working with nonvariola orthopoxviruses [e.g., vaccinia and monkeypox][6]. In 1984, these recommendations were included in guidelines for biosafety in microbiological and biomedical laboratories [7]. These guidelines expanded the recommendation to include persons working in animal-care areas where studies with orthopoxviruses were being conducted and recommended that these workers have documented evidence of satisfactory smallpox vaccination within the preceding 3 years. CDC has provided vaccinia vaccine for these laboratory workers since 1983 [8].
Because studies of recombinant vaccinia virus vaccines have been advanced to the stage of clinical trials, health-care workers [e.g., physicians and nurses] may now be exposed to vaccinia and recombinant vaccinia viruses and should be considered for vaccinia vaccination.
VACCINIA VACCINE
The vaccinia vaccine currently licensed in the United States is a lyophilized preparation of infectious vaccinia virus. * The vaccine was prepared from calf lymph with a seed virus derived from the New York City Board of Health [NYCBOH] strain of vaccinia; it has a concentration of 10 superscript 8 pock-forming units [PFU] per milliliter. Vaccine is administered by using the multiple-puncture technique with a bifurcated needle.
After percutaneous administration of a standard dose of vaccinia vaccine, >95% of primary vaccinees [i.e., persons receiving their first dose of vaccine] will develop neutralizing or hemagglutination inhibition antibody at a titer of greater than or equal to 1:10 [9]. Neutralizing antibody titers of greater than or equal to 1:10 are found among 75% of persons for 10 years after receiving second doses and up to 30 years after receiving three doses of vaccine [10,11]. The level of antibody that protects against smallpox [variola]infection is not known, but epidemiologic studies suggest that protection against smallpox persists a minimum of 5 years after revaccination [12]. Also, the level of antibody required for protection against vaccinia infection is not known. However, when the response to revaccination is used as an indication of immunity, 30% of persons with titers