Conjugate vaccines for enteric fever: proceedings of a meeting organized in New Delhi, India in 2009

Abstract

Enteric fever is responsible for significant morbidity in South Asia and high prevalence of severe disease is seen in children under two years of age. Effective typhoid vaccines are available, but they cannot be used for children under two years of age and also have some limitations in older age groups. Participants supported development of a Salmonella Typhi conjugate vaccine able to induce effective, long-lasting immunity in young children. The role of Salmonella Paratyphi A as a cause of enteric fever was discussed and consensus reached that a bivalent S. Typhi-S. Paratyphi A conjugate vaccine is highly desirable; however, considering disease epidemiology and the advanced status of vaccine development, rapid introduction of monovalent S. Typhi conjugate vaccine into vaccination programs of South Asia was recommended. Prevention should be emphasized, available vaccines used, and efforts toward improving sanitation continued. Success of the new vaccine will depend on several factors, including delivery costs and governmental ability to adopt and implement suitable immunization programs. To ensure good immunization coverage, the conjugate vaccine could be administered either to young infants, concomitantly with infant EPI vaccines, or to older infants, concomitantly with measles vaccine, currently given at 9 to 12 months. The need for new combination vaccines, containing both EPI and typhoid antigens, was discussed as a tool to increase coverage and reduce the number of injections and priority conflicts in a crowded infant vaccination schedule. However, stand-alone enteric fever conjugate vaccines would allow more flexibility to immunize different age groups and therefore should be rapidly developed.

Safety, Immunogenicity and Dose Ranging of a New Vi-CRM197 Conjugate Vaccine against Typhoid Fever: Randomized Clinical Testing in Healthy Adults

“…However, these vaccines have limitations; the Vi polysaccharide vaccine cannot be administered to subjects younger than 2 years and, even in pre-school children, its efficacy is controversial [10]. Additionally, polysaccharide vaccines do not induce immunological memory, require frequent boosters, to maintain adequate protection, and may be associated with hyporesponsiveness [11].…”

Parallel Exploitation of Diverse Host Nutrients Enhances Salmonella Virulence

“…Enteric fever causes tremendous morbidity and mortality worldwide. Current control strategies become increasingly inefficient as a result of increasing antimicrobial resistance [22], [23] and emergence of Salmonella serovars that are not covered by currently available safe vaccines [24], [25].…”

Stochastic Simulation of Endemic Salmonella enterica Serovar Typhi: The Importance of Long Lasting Immunity and the Carrier State

“…While vaccination is recommended by WHO for campaign vaccination of school age children [3], uptake has been limited. The clinical development of a conjugate vaccine [4]–[6], expected to have higher efficacy and to protect for longer and to be effective in infants, highlights the need for quantitative understanding of the dynamics of transmission and immunity.…”