Smallpox: a review of clinical disease and vaccination.

The clinical course of smallpox infection and the current and future roles of vaccination and strategies for controlling smallpox outbreaks are reviewed. Close personal contact is required for transmission of variola, the DNA virus that causes smallpox. Following an incubation period, infected persons have prodromal symptoms that include high fever, back pain, malaise, and prostration. The eruptive stage is characterized by maculopapular rash that progresses to papules, then vesicles, and then pustules and scab lesions. The mortality rate for smallpox is approximately 30%. Patients having a fever and rash may be confused with having chickenpox. The most effective method for preventing smallpox epidemic progression is vaccination. Until recently, only 15 million doses of smallpox vaccine--manufactured 20 years ago--were available in the United States. The vaccine is a live vaccinia virus preparation administered by scarification with a bifurcated needle. The immune response is protective against orthopoxviruses, including variola. Vaccination is associated with moderate to severe complications, such as generalized vaccinia, eczema vaccinatum, progressive vaccinia, and postvaccinial encephalitis. Efforts for vaccine production are now focused on a live cell-culture-derived vaccinia virus vaccine. Although smallpox was eradicated in 1980, it remains a potential agent for bioterrorism. As a category A biological weapon, its potential to devastate populations causes concern among those in the public health community who have been actively developing plants to deal with smallpox and other potential agents of biological warfare. The only proven effective strategy against smallpox is vaccination.