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 × 10(r) cfu dose, while 40 each received one or two 5 × 10⁹cfu doses. Vibriocidal antibody (the best correlate of immunity) seroconversion was lower in soldiers than civilians (P <.001). Increasing the vaccine dose to 5 × 10⁹cfu raised the geometric mean titer (P <.001). A second 5 × 10⁹cfu dose one week later did not notably increase serocon- versions. Likelihood of seroconversion was inversely correlated with baseline vibriocidal titer (P <.001). CVD 103-HgR caused seroconversion in most subjects with baseline titers <1:40, including 100% of civilians after one 5 × 10(r) cfu dose, 79% of soldiers after one 5 × 10⁹cfu dose, and 45% of soldiers after one 5 × 10^scfu 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 × 10⁹cfu dose.