SAFETY AND IMMUNOGENICITY OF DIFFERENT IMMUNIZATION REGIMENS OF CVD 103-HGR LIVE ORAL CHOLERA VACCINE IN SOLDIERS AND CIVILIANS IN THAILAND

Attenuated Vibrio cholerae oral vaccine CVD 103-HgR was well tolerated by 324 Thai soldiers and civilians. Most received a single 5 x 10(8) cfu dose, while 40 each received one or two 5 x 10(9) cfu doses. Vibriocidal antibody (the best correlate of immunity) seroconversion was lower in soldiers than civilians (P < .001). Increasing the vaccine dose to 5 x 1O(9) cfu raised the geometric mean titer (P < .00 1). A second 5 x 1O(9) cfu dose one week later did not notably increase seroconversions. Likelihood of seroconversion was inversely correlated with baseline vibriocidal titer (P < .001). CVD 103-HgR caused seroconversion in most subjects with baseline titers less-than-or-equal-to 1:40, including 100% of civilians after one 5 x 10(8) cfu dose, 79% of soldiers after one 5 x 10(9) cfu dose, and 45% of soldiers after one 5 x 10(8) cfu dose. In persons with elevated baseline titers, vibriocidal antibody seroconversion is not a sensitive measure of whether vaccine has boosted intestinal immunity; for such subjects, other measurements must be used. Study regimens in endemic areas should use a single 5 x 10(9) cfu dose.