Antibodies elicited by altSonflex1-2-3 GMMA vaccine are bactericidal against a panel of drug-resistant Shigella clinical isolates

Shigellosis significantly impacts global health, particularly affecting vulnerable populations in low- and middle-income countries, with over 270 million annual infections. It also causes morbidity in specific high-risk groups in high-income countries. Antibiotic treatment is increasingly compromised by multidrug-resistant strains, highlighting the urgent need for a <i>Shigella</i> vaccine. We developed a four-component O-antigen-based vaccine candidate targeting <i>Shigella sonnei</i> and <i>Shigella flexneri</i> 1b, 2a, and 3a serotypes, named altSonflex1-2-3, to provide broad protection against most globally prevalent <i>Shigella</i> strains. Here, we characterized the O-antigen structural features of a panel of <i>S. flexneri</i> drug-resistant clinical isolates and verified that they did not significantly differ from the O-antigen in the vaccine. Preclinical sera elicited by altSonflex1-2-3 were bactericidal against most strains, confirming the ability of anti-O-antigen antibodies to recognize and kill <i>in vitro</i> different clinical isolates. Importantly, our results suggest that altSonflex1-2-3 could offer protection against antimicrobial-resistant <i>Shigella</i> strains, addressing a critical public health issue.