Laboratory-acquired vaccinia exposures and infections--United States, 2005-2007

The last case of naturally acquired smallpox disease, caused by the orthopoxvirus variola virus (VARV), occurred in 1977, and the last laboratory-acquired case occurred in 1978. Smallpox was eradicated largely as the result of a worldwide vaccination campaign that used the related orthopoxvirus, vaccinia virus (VACV), as a live virus vaccine. Routine childhood vaccination for smallpox in the United States was terminated by 1972, but vaccination continues or has been reintroduced for specific groups, including laboratory workers who may be exposed to orthopoxviruses, members of the military, selected health-care workers, and first responders. Severe complications of VACV infection can occur, particularly in persons with underlying risk factors, and secondary transmission of VACV also can occur. VACV is used in numerous institutions for various research purposes, including fundamental studies of orthopoxviruses and use as a vector for the expression of foreign proteins (often antigens or immunomodulators) in eukaryotic cells and animal models. The widespread use of VACV for research has resulted in laboratory-acquired VACV infections, some requiring hospitalization. The current Advisory Committee on Immunization Practices (ACIP) guidelines recommend VACV vaccination for laboratory workers who handle cultures or animals contaminated or infected with nonhighly attenuated VACV strains or other orthopoxviruses that infect humans. This report describes five recent occurrences of laboratory-acquired VACV infections and exposure and underscores the need for proper vaccination, laboratory safety, infection-control practices, and rapid medical evaluation of exposures in the context of orthopoxvirus research.