Varicella susceptibility and vaccination strategies in young adults.

BACKGROUND Varicella infection causes substantial morbidity in young adults. Most military basic trainees are 18 to 21 years old, yet the Army has no varicella vaccination policy. We therefore determined varicella susceptibility in a population of Army basic trainees, examined variables that might predict antibody status, and developed a vaccination strategies model. METHODS Fifteen-hundred ninety-five trainees completed a demographic and historical questionnaire. Varicella antibody status was determined on 1201 volunteers. These data plus information from the literature were used to construct a decision tree of vaccination strategies that was applied to the total population of Army basic trainees in 1995 (n = 65,298). RESULTS Fifty (4.2 percent) of 1201 soldiers were antibody negative. Trainees who lived with no or 1 sibling while growing up were most likely to be seronegative (P < 0.01). The positive predictive value of a history of varicella was 98.5 percent, whereas the negative predictive value of a negative history of varicella was 23 percent. In the vaccination strategies model, serologically testing soldiers with a negative history of varicella and vaccinating those without protective antibodies was the most cost-effective approach. CONCLUSIONS In young adults a positive varicella history accurately predicts immunity, but verification of a negative history with antibody testing is recommended before vaccination.