Effect of timing of hepatitis B vaccine doses on response to vaccine in Yucpa Indians.

In a large hepatitis B prevention programme, hepatitis B vaccine was given in standard doses to greater than 1000 susceptible Yucpa Indians between 1983 and 1985. Thirteen months after the programme began, 373 vaccine recipients were tested using commercial radioimmunoassay to titre antibody response to the vaccine. Because of logistic difficulties, only 32% had received vaccine by the recommended schedule (second and third doses at one and six months after the first, respectively). The second and third doses were received early by 4 and 31%, respectively, and 27 and 16% received these doses later than intended. Overall response to vaccine was excellent: 98% of vaccinees developed anti-HBs greater than 10 mIU (geometric mean titre 688 mIU). Multivariate analysis showed that the response to vaccination was inversely related to the age of the vaccinee and directly related to the timing of the third vaccine dose. In particular, those receiving the third vaccine dose late (greater than 7 months after the first dose) developed antibody titres two-fold higher than those receiving the third dose on schedule (p less than 0.01). The response to vaccination was not significantly related to the timing of the second dose. A satisfactory response was obtained with various schedules of dose timing, including early second and third doses, late second and third doses and late second but normal third doses. These findings suggest that the response to hepatitis B vaccine is not highly dependent on timing of vaccine doses and that modest alterations in timing of doses, such as those necessary to integrate hepatitis B vaccine with other childhood vaccines, do not affect the excellent response to this vaccine.