IMMUNOLOGICAL RESPONSE TO VIBRIO-CHOLERAE O1 INFECTION AND AN ORAL CHOLERA VACCINE AMONG PERUVIANS

A 'double-blind', randomized, placebo controlled study of an oral inac tivated whole cell plus recombinant B subunit (WC/rBS) cholera vaccine was conducted during February-March 1992 in Peru in 346 military recr uits, 307 (89%) of whom received 2 oral doses of vaccine or Escherichi a coli K12 placebo 2 weeks apart. Paired serum samples were obtained f rom 155 (50%) of the recipients of 2 doses. An epidemic of cholera too k place between doses. No difference in cholera attack rates was detec ted between vaccine and placebo recipients after one dose (8% versus 1 4%). Seroconversion (4-fold or higher increase in vibriocidal antibody titres) was detected in 90% and 80% of vaccine and placebo recipients , respectively, with low pre-existing vibriocidal titres (< 0.01). The anti-cholera toxin seroconversion rate among those with low pre-exist ing titres was higher in vaccinated subjects (97%) than in placebo rec ipients (68%) (P < 0.01). Administration of 2 doses of WC/rBS vaccine concomitantly with natural V. cholerae O1 infection enhanced the serum anti-cholera toxin response. The immune response to the whole cell co mponent of the vaccine was reduced by high pre-existing vibriocidal an tibody titres.