Abstract
Typhoid fever, caused by Salmonella Typhi, remains a significant global public health concern, with an estimated 11 - 20 million cases annually. Vaccines are critical to controlling typhoid fever. Widespread vaccination diminishes the emergence of antibiotic-resistant strains of S. Typhi. The economic benefits of vaccination are also substantial, as the costs of treating typhoid fever and its complications can be significant. Ty21a(®), a killed whole-cell vaccine, and Vivotif(®), a live-attenuated vaccine, have been available for decades but have relatively short durations of action and only provide partial protection. Vi polysaccharide-conjugate vaccines have improved the durability of protection, but there is still room for improvement. Typhax(™), a novel alternative to traditional conjugate vaccines, utilizes Vi polysaccharide that is non-covalently entrapped in a poly-L-lysine and CRM197 protein matrix crosslinked by glutaraldehyde. When formulated with Advax-CpG(™) adjuvant, Typhax demonstrated promising results in a range of animal models including mice, rabbits, and non-human primates in which it induces high and sustained serum anti-Vi immunoglobulin G and serum bactericidal activity, without any safety or reactogenicity issues. This novel vaccine approach offers the potential for a low-cost, more effective, and durable vaccine against typhoid fever, avoiding the need for frequent booster doses.