[Mild varicella observed in children vaccinated with varicella vaccine between 1984 and 1987]

We investigated varicella cases developed in children who received varicella vaccine in the period from October 1984 to March 1987. In this period 463 children were vaccinated and 334 of the vaccines were seronegative before injection. Seroconversion was observed in 276 seronegative vaccinees producing a seroconversion rate of 83.1%. Thirty-five children developed exanthem more than 4 weeks after the vaccination and were diagnosed as varicella. Among them one child was found to be antibody-positive in his preserum and five were seronegative in both their pre- and post-sera. Thus, among the children who were seroconverted by the vaccination only 30 had varicella (the attack rate = 10.9%). No varicella cases were reported, however, among 27 children who first became seropositive after revaccination. When these children were added to the seroconverted ones, the case rate amounted to 9.9% (30/303). The general symptoms of varicella observed in the vaccinated children were mild or extremely mild, so varicella vaccine is reasonably indicated to be efficient and useful although it could no completely protect the vaccinees from natural varicella.