Salmonella Typhi Vi polysaccharide conjugate vaccine protects infants and children against typhoid fever

• Published in: The Lancet (British edition) Vol. 398; no. 10301; pp. 643 - 644
• Main Authors: Crump, John A, Oo, Win Thandar
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 21.08.2021; Elsevier Limited
• Subjects: Children; Cluster analysis; Conjugates; Consortia; COVID-19; Drug resistance; Encephalitis; Fever; Infants; Polysaccharides; Population density; Salmonella; Tetanus; Typhoid; Urban areas; Vaccines; Vector-borne diseases; Waterborne diseases; India
• ISSN: 0140-6736; 1474-547X
• DOI: 10.1016/S0140-6736(21)01340-4

The past decade has seen remarkable progress in our understanding of the scale of the global typhoid fever problem,1 the alarming emergence in south Asia of extensively drug-resistant Salmonella enterica serovar Typhi (S Typhi) threatening effective treatment,2 and the WHO prequalification of a typhoid conjugate vaccine,3 a new tool to prevent disease. In The Lancet, Firdausi Qadri and colleagues report the analysis to 18 months of follow-up of a cluster-randomised trial of the WHO prequalified S Typhi Vi polysaccharide tetanus toxoid conjugate vaccine (Vi-TT; Tybar TCV, Bharat Biotech International, Hyderabad, India) among infants and children aged 9 months to younger than 16 years in the densely populated and highly mobile urban area of Mirpur, Dhaka, Bangladesh.4 Compared with the SA 14-14-2 Japanese encephalitis vaccine control group, Vi-TT conferred 85% (97·5% CI 76–91, p<0·0001) total protection. Follow-up ended early at 18 months, and the plan to target the primary analysis to the inner 80% of clusters, a strategy that showed promise in a re-analysis of the Kolkata unconjugated Vi polysaccharide vaccine trial,9,12 reverted to a traditional whole cluster analysis.4 Patterns of typhoid transmission can vary substantially by setting and might have considerable influence on the ability to demonstrate herd protection, if present.