OVER 5-YEAR FOLLOW-UP OF OKA MERCK VARICELLA VACCINE RECIPIENTS IN 465 INFANTS AND ADOLESCENTS/

A total of 465 healthy infants and adolescents ages 12 months to 17 ye ars without a known history of varicella or recent exposure to varicel la-zoster virus VZV were immunized with live attenuated Oka/Merck vari cella vaccine from November, 1984, through April, 1989. The vaccine ad ministered was from 1 of 7 production lots containing front 950 to 326 5 plaque-forming units and was well-tolerated with few side effects. T he seroconversion rate for seronegative subjects was 94.6% (403 of 426 ). This varied by lot from 85% (950 plaque-forming units) to 100% (301 0 and 3265 plaque-forming units), Breakthrough disease after exposure to varicella in seroconverters during 5 to 10 years of follow-up was 1 8.6% (75 of 403). The breakthrough disease was characterized by a macu lopapular rash with a median of 35 lesions, most of which were macules . Breakthrough disease lasted a median of 5 days and the median temper ature was 99 degrees F; 65.3% (49 of 75) of subjects were afebrile and 2.7% (2 of 75) of subjects had temperatures of >102.9 degrees F. Vari cella vaccine provides excellent (94.6%) seroconversion, and most chil dren who developed breakthrough disease (18.6%) experienced a modified , milder form of illness than has been observed with natural varicella in unvaccinated subjects.