obsolete CVD 1204(pGA1-CS2) true Oliver He An aroA and virG mutant (CVD 1203) is attenuated in guinea pigs, as shown by the Sereny test. Guinea pigs inoculated with CVD 1203 were also protected from challenge with wild type S. flexneri Rebecca Racz Shigella flexneri 2a strain CVD 1203 vaccine terms merged