Objectives: To investigate the safety of live attenuated varicella vaccine (Oka strain) and the optimal virus titre/dose required for immunogenicity in healthy South African children.
Design: Double-blind randomised clinical study using two different lots of varicella vaccine, each at two different titres. Subjects were randomly allocated to groups 1, 2, 3 and 4 to receive vaccine containing a mean virus titre of 10(4,5), 10(3,1), 10(3,9) and 10(2,7) PFUs per dose respectively. Clinical signs and symptoms were followed up for 42 days post-vaccination. Specific varicella antibodies were measured by an indirect immunofluorescence method in sera obtained on day 0 and day 42.
Setting: City Health Clinic, Chatsworth, Durban.
Participants: A total of 200 healthy 9-24-month-old children were vaccinated, of whom 189 (44,5%) completed the study.
Main outcome measures: Pre- and post-vaccination varicella antibody levels. Adverse events following varicella vaccination.
Results: The vaccine was safe and well tolerated. No local symptoms were reported. Skin reactions were specifically solicited in this study: 21 reactions were reported in 8.5% (17/200) of children. Vesicles were reported in 2 vaccines (< or = 10 vesicles in both cases). One serious adverse event was reported: hospitalisation for bronchopneumonia on day 16 post-vaccination which resolved without sequelae. Around day 42 post-vaccination (range 35-63 days) all the 176 initially seronegative subjects had seroconverted for varicella antibodies. Post-vaccination geometric mean titres (GMTs) were 104.1, 66.2, 69.5 and 77.0 for groups 1-4 respectively. Six subjects who were initially seropositive maintained or increased their titres post-vaccination; 3 of the 6 showed a booster response (a > or = 4-fold increase from the pre-vaccination titre).
Conclusions: Varicella vaccine was found to be safe, immunogenic and well tolerated. No difference in seroconversion rates or GMTs, either between groups receiving the two vaccine lots or between groups receiving the different titres of each lot, was shown.