A nontoxic cholera enterotoxin (CT) analog is chimeric with regard to both epitypes of CT-B subunits, CT-B-1 and CT-B-2.

The gene encoding a nontoxic analog, CT-2*, of cholera enterotoxin (CT) with attenuating codon substitutions in the A subunit was introduced into the attenuated Vibrio cholerae classical biotype mutant candidate vaccine strain CVD103, which produces the B subunit (but not the A subunit) of CT-1. The recombinant strain produces a chimeric nontoxic analog holotoxin containing both CT-B-1 and CT-B-2 subunits. This offers potential advantages over CVD103 in the induction of immunity against E1 Tor biotype and V. cholerae O139 strains which produce CT-B-2. The recombinant protein may also be useful in polysaccharide-protein conjugate vaccines against both O1 and O139 serovars of V. cholerae.