The capsular polysaccharide of Salmonella typhi (Vi) is a licensed vaccine but with limited efficacy in children less than 5 years old. To provide a vaccine for younger children, Vi was conjugated to recombinant exoprotein A of Pseudomonas aeruginosa (rEPA). An efficacy of 89% at 47 months was shown in 2-to-5-year olds injected with Vi-rEPA. Safety and immunogenicity of Vi-rEPA, administered concurrently with routine vaccines in the Expanded Program of Immunization (EPI) at 2, 4, 6 and 12 months were evaluated in 301 Vietnamese infants. Controls received Hib-TT +EPI or EPI alone. No serious adverse events occurred in any groups. The GM IgG anti-Vi level in the Vi-rEPA group was significantly higher than in the control groups;one month after the last injection 90% infants had higher than the estimated protective level. There was no difference in the level of IgG antibodies to the toxoids of diphtheria (DT), tetanus (TT) and to pertussis toxin among all groups;Vi-rEPA is suitable for routine immunization in infants. In collaboration with the International Vaccine Institute and Novartis Institute for Global Health, Vi was conjugated to licensed vaccines such as DT and TT. In mice, these conjugates elicited similar IgG anti-Vi levels to those induced by Vi-rEPA. Salmonella paratyphi A (SPA) is the second most common cause of enteric fever in developing countries, transmitted through ingestion of food or drink contaminated by infected persons. A chronic carrier was identified in an investigation of SPA outbreak by measuring serum anti-LPS levels among SPA infections (rectal swab positive individuals). In collaboration with the Guangxi Center for Disease Prevention and Control an expanded survey was initiated in a high endemic area to screen for potential chronic carriers. Vibrio cholerae O1 remains a major health problem in the Indian subcontinent and in Africa. Field studies showed that serum vibriocidal activity is directed toward its LPS. In a phase 1 trial, V. cholera O-SP conjugates elicited IgG anti-LPS with vibriocidal activity. A hexamer corresponding to the O-SP was chemically synthesized and conjugated to TT. In mice this conjugate elicited higher vibriocidal activities than the native O-SP conjugate used in the Phase I study. Various linker lengths were studied. A conjugate synthesized with a heptadecamer linker was more immunogenic than the one with a nonamer linker. Rotavirus is the most common cause of infantile diarrhea worldwide. Two licensed oral rotavirus vaccines confer limited protection and some lots were found to contain small amounts of porcine circovirus 1 and 2 DNA. We are designing a parenteral vaccine based on capsid proteins. Recombinant capsid proteins with truncated C or N termini were expressed in E. coli and elicited neutralizing antibodies in mice and guinea pigs. Conjugation of the recombinant proteins to polysaccharide vaccines improved protein solubility. The core region of the capsid protein was also investigated. Comparison of immunogenicity of the core with the full length protein will be conducted in mice. Enterohemorrahagic E. coli (EHEC) infections are the leading cause of E. coli deaths in developed countries. In the US, the prevalent serotype is O157H:7. EHEC strains contain the Shiga toxin (Stx) gene and the released toxin can cause the following manifestations;from diarrhea, hemorrhagic colitis, to hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura. HUS is a major cause of acute and chronic kidney damage in young children and could lead to death. In a phase II study in 2-5 years old children in the US, an LPS based conjugate vaccine elicited a >10 fold rise of antibodies with bactericidal activity in 98% the children. An infant safety and immunogenicity study is planned. Most EHEC infections are caused by strains secreting Stx2. The non-toxic B-subunit of Stx2 was purified in high yield by an improved recombinant technique. Stx2B could serve as a carrier protein for the E. coli O157 O-SP conjugate vaccine to provide a broader coverage.
