CLINICAL SURVEY OF NATURAL VARICELLA COMPARED WITH BREAKTHROUGH VARICELLA AFTER IMMUNIZATION WITH LIVE ATTENUATED OKA MERCK VARICELLA VACCINE

Objective. To prospectively characterize varicella occurring in childr en previously immunized with a live attenuated varicella vaccine (brea kthrough varicella) through daily observation by medical personnel and to compare it with natural varicella followed in the same manner. Des ign. A blinded clinical survey. Setting. Four pediatric practices (two private; two hospital-based). Participants. Healthy 12-month-old thro ugh 17-year-old children with chickenpox were studied; 92 had natural varicella and 58 had breakthrough varicella. Selection procedures and interventions. Study personnel, unaware of vaccination status, documen ted the clinical characteristics of each patient in the office or at t he patient's home each day from enrollment until the day after the tot al number of lesions increased less than 10%. A standard form document ing number and description of lesions, temperature, duration of illnes s, and associated clinical complaints was completed each day by the sa me study personnel. Acute and convalescent sera were obtained on break through cases. Measurements and results. Antibody to varicella-zoster virus was measured by the glycoprotein-based enzyme-linked immunosorbe nt assay. Of those with sera available, 85% were serologically confirm ed. Eighty-seven percent of enrollees had a known exposure to chickenp ox, with at least two thirds of each group having a greater than 4-hou r or a household exposure. The numbers of total and vesicular lesions were significantly higher in the natural varicella group, regardless o f exposure status (P = .021 to <.001). The group with breakthrough var icella had a significantly lower incidence of fever (P < .001) and a s ignificantly shorter duration of illness (P < .001). Other associated constitutional complaints and complications were not significantly dif ferent between groups. Conclusion. Varicella in vaccine recipients is clinically modified and significantly less severe than natural disease .