Abstract 19 Poster Session 1, Saturday, 5/1 (poster 233)

OBJECTIVE: To determine the effect of dosing schedule and other biologic factors on the rates of seroprotection achieved 12 months after the initiation of the hepatitis B (hepB) vaccination series.

DESIGN: Prospective cohort design. 943 participants from a hospital-based and a school-based clinic were enrolled. Demographic data were obtained from patient questionnaires. Participants received the first hepB immunization after baseline serologies were obtained. Participants were told the correct dosing schedule for the vaccination (0, 1, and 6 months), however, participants returned at varying time intervals. Serology titers were obtained 12 months after initiation of the series. Seroprotection (SP) was defined as a titer level ≥10 IU/L. Participants were excluded from this analysis if they had positive baseline serologies (n=44), had received vaccine elsewhere (n=29), or were noncompliant with the 12 month visit (n=351). Data were analyzed using chi square analysis, Student's t test, and logistic regression models.

RESULTS: 519 participants were eligible for analysis of 12 month seroprotection data. 61 participants had received only one immunization at the time of the 12 month visit with 19.7% achieving seroprotection. 171 participants had received 2 immunizations at varying time intervals with 69.6% achieving seroprotection. 287 participants had completed the series at varying dosing schedules before the 12 month visit with 98.6% achieving seroprotection. On bivariate analysis, age, race, vitamin and iron pill use, presence of a chronic illness, alcohol and marijuana use, and smoking were not associated with achieving seroprotection. When controlling for the number of immunizations received, gender and oral contraceptive use lost bivariate association with seroprotection. The number of immunizations received (completing the series 1 or 2 immunizations) (P=0.018) and lower body mass index (BMI) (P<0.001) were associated with seroprotection. For participants who received only 2 immunization, a logistic regression model including the variables of BMI and time in months to the second immunization revealed that seroprotection was not affected by time to the second immunization while BMI (OR=0.93, 95% CI=0.87-0.98) remained a significant predictor. For those completing the series, a logistic regression model including BMI, month of the second shot, month of the third short, and the interval between the second and third shots revealed that BMI (OR=0.83, 95% CI=0.69-0.98) remained the only significant predictor of seroprotection.

CONCLUSIONS: Dosing schedule within 12 months of initiating the hepB vaccination series does not affect the achievement of seroprotection among adolescents. The number of immunizations clearly affects rates of seroprotection, and health care providers may want to consider an adolescent's BMI when determining appropriate vaccination dosing.