Typhoid fever vaccines

Immune responses to Vi capsular polysaccharide typhoid vaccine in children 2 to 16 years old in Karachi, Pakistan, and Kolkata, India

The geometric mean concentration (GMC) and the proportion maintaining a protective level (150 enzyme-linked immunosorbent assay (ELISA) units [ELU]/ml) 2 years following a single dose of 25 μg of injectable Vi capsular polysaccharide typhoid vaccine was measured against that of the control hepatitis A vaccine in children 2 to 16 years old in cluster randomized trials in Karachi and Kolkata. The GMC for the Vi group (1,428 ELU/ml) was statistically significantly different from the GMC of the control hepatitis A vaccine group (86 ELU/ml) after 6 weeks. A total of 117 children (95.1%) in the Vi group and 9 (7.5%) in the hepatitis A group showed a 4-fold rise in Vi IgG antibody concentrations at 6 weeks (P < 0.01). Protective antibody levels remained significantly different between the two groups at 2 years (38% in the Vi vaccine groups and 6% in the hepatitis A group [P < 0.01]). A very small proportion of younger children (2 to 5 years old) maintained protective Vi IgG antibody levels at 2 years, a result that was not statistically significantly different compared to that for the hepatitis A group (38.1% versus 10.5%). The GMCs of the Vi IgG antibody after 2 years were 133 ELU/ml for children 2 to <5 years old and 349 ELU/ml for children 5 to 16 years old. In conclusion, Vi capsular polysaccharide typhoid vaccine is immunogenic in children in settings of South Asia where typhoid is highly endemic. The antibody levels in children who received this vaccine remained higher than those in children who received the control vaccine but were significantly reduced at 2 years of follow-up.

Reliable means of diagnosis and serovar determination of blood-borne Salmonella strains: quick PCR amplification of unique genomic loci by novel primer sets

Typhoid fever is becoming an ever increasing threat in the developing countries. We have improved considerably upon the existing PCR-based diagnosis method by designing primers against a region that is unique to Salmonella enterica subsp. enterica serovar Typhi and Salmonella enterica subsp. enterica serovar Paratyphi A, corresponding to the STY0312 gene in S. Typhi and its homolog SPA2476 in S. Paratyphi A. An additional set of primers amplify another region in S. Typhi CT18 and S. Typhi Ty2 corresponding to the region between genes STY0313 to STY0316 but which is absent in S. Paratyphi A. The possibility of a false-negative result arising due to mutation in hypervariable genes has been reduced by targeting a gene unique to typhoidal Salmonella serovars as a diagnostic marker. The amplified region has been tested for genomic stability by amplifying the region from clinical isolates of patients from various geographical locations in India, thereby showing that this region is potentially stable. These set of primers can also differentiate between S. Typhi CT18, S. Typhi Ty2, and S. Paratyphi A, which have stable deletions in this specific locus. The PCR assay designed in this study has a sensitivity of 95% compared to the Widal test which has a sensitivity of only 63%. As observed, in certain cases, the PCR assay was more sensitive than the blood culture test was, as the PCR-based detection could also detect dead bacteria.

Bacteremic typhoid fever in children in an urban slum, Bangladesh

We confirmed a bacteremic typhoid fever incidence of 3.9 episodes/1,000 person-years during fever surveillance in a Dhaka urban slum. The relative risk for preschool children compared with older persons was 8.9. Our regression model showed that these children were clinically ill, which suggests a role for preschool immunization.

Technologies to improve immunisation safety

Ever since a vaccine was first used against smallpox, adverse events following immunisation have been reported. Adverse reactions may be caused by a fault in vaccine production, idiosyncratic responses or unsafe handling and vaccine administration practices. Technological advances that promise to bypass many of the dangers currently associated with vaccine administration are described. Plans for the next decade and beyond include developing injection-free systems for vaccine delivery that overcome the limitations of current immunisation programmes and help prevent programmatic mistakes. Also under development are new parenteral administration devices such as the auto-disable syringe and the mono-dose pre-filled device, and mucosal and transcutaneous immunisation systems. Training needs to be at the forefront of efforts to limit human error. Above all, there must be a willingness to respond to new climates and new technologies in order to ensure safe immunisation of children globally.