Introduction
®, bacterial infection, oral Ty21a vaccine, typhoid conjugate vaccine, typhoid
TYPHOID, BACTERIAL INFECTION, TYPHOID
Typhoid, a bacterial infection caused by At present, the vaccines available for typhoid are of 3 main types- Vi polysaccharide (ViPS) vaccine, typhoid conjugate vaccine (TCV), and live attenuated oral Ty21a vaccine. Conjugation, i.e. coupling to protein carriers, transforms the T cell-independent polysaccharide vaccines to T cell-dependent antigenic vaccines and thus enhances their immunogenicity and utility in infants and younger children.In January 2018, WHO prequalified the first conjugate vaccine for typhoid, Typbar TCV® in age 6 months and above.The protective efficacy of a single dose of Vi polysaccharide-tetanus toxoid (Vi-TT) conjugate vaccine (Typbar TCV) as part of Typhoid Vaccine Acceleration Consortium (TyVac) in Nepal was above 80% in first year and above 70% in second year.The International Vaccine Institute (IVI) developed and transferred technology to SK Bioscience (Seoul, South Korea) for a TCV consisting of diphtheria toxoid conjugated purified Vi polysaccharide from S Typhi strain C6524 (Vi-DT), targeting WHO prequalification and aid in the global supply of TCVs. The results of phase 1 and 2 studies of the Vi-DT vaccine conducted in the Philippines have demonstrated safety good immunogenicity.