IMMUNOGENICITY AND SAFETY OF A LIVE ATTENUATED VARICELLA VACCINE IN HEALTHY INDIAN CHILDREN AGED 9-24 MONTHS

Objectives. To investigate the safety of live attenuated varicella vac cine (Oka strain) and the optimal virus titre/dose required for immuno genicity in healthy South African children. Design. Double-blind rando mised clinical study using two different lots of varicella vaccine, ea ch 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, Clinica l signs and symptoms were followed up for 42 days post-vaccination. Sp ecific varicella antibodies were measured by an indirect immunofluores cence method in sera obtained on day 0 and day 42, Setting. City Healt h 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, Resul ts. The vaccine was safe and well tolerated. No local symptoms were re ported, Skin reactions were specifically solicited in this study: 21 r eactions were reported in 8,5% (17/200) of children, Vesicles were ; r eported in 2 vaccines (less than or equal to 10 vesicles in both cases ). One serious adverse event was reported: hospitalisation for broncho pneumonia on day 16 post-vaccination which resolved without sequelae, Around day 42 postvaccination (range 35 - 63 days) all the 176 initial ly seronegative subjects had seroconverted for varicella antibodies, P ost-vaccination geometric mean titres (GMTs) were 104,1, 66,2, 69,5 an d 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 greater than or equal to 4-fold increase from the pre-vaccination titre), Conclusions, Varicella vacci ne 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 e ach lot, was shown.