ZH9PA

ZH9PA is a genetically modified, live attenuated bacterial vaccine candidate developed for the prevention of paratyphoid fever caused by Salmonella enterica serovar Paratyphi A. It is derived from the S. Typhi ZH9 strain, which itself is an attenuated S. Typhi Ty2 strain with deletions in the aroC and ssaV genes to ensure safety and prevent disease-causing capability[1][3][6]. ZH9PA has been further engineered to express antigens specific to S. Paratyphi A, including modifications in flagellin (fliC gene) and lipopolysaccharide (rfbE replaced with wbdR), enabling it to induce immune responses against S. Paratyphi A[5][6]. The vaccine is being developed as part of a bivalent oral formulation (with ZH9) targeting both typhoid and paratyphoid fever—diseases for which there remains significant unmet need, especially as no licensed vaccine currently exists for paratyphoid fever[3][5]. The developer is Prokarium.