A typhoid conjugate vaccine (TCV) recently prequalified by the World Health Organization (WHO) was shown to be efficacious in a human challenge model.

The aim of a study in The New England Journal of Medicine was to retrieve data on the efficacy of TCV from efficacy trials in areas where typhoid is endemic.

This was a phase III, randomized, controlled, double-blinded trial undertaken in Lalitpur, Nepal, wherein children between 9 months and 16 years of age were randomly assigned in a 1:1 ratio, to receive either a TCV or a capsular group A meningococcal conjugate vaccine (MenA) – as a control. The primary outcome was typhoid fever confirmed by blood culture.

Overall, 10005 participants received the TCV and 10014 received the MenA vaccine. Typhoid fever occurred in seven participants who received TCV – 79 cases per 100,000 person-years, and in 38 who received MenA vaccine – 428 cases per 100,000 person-years. Overall, 132 serious adverse events—61 in the TCV group and 71 in the MenA vaccine group—occurred in the first 6 months. Only one event (pyrexia) was vaccine-related; the participant remained unaware of the trial-group assignment. Similar rates of adverse events were noted in the two trial groups – fever developed in 5% of participants in the TCV group and 5.4% in the MenA vaccine group in the first week after vaccination. While in the immunogenicity subgroup, seroconversion was 99% in the TCV group and 2% in the MenA vaccine group.

Hence, a single dose of TCV was immunogenic and effective in reducing S. Typhi bacteremia in children aged from 9 months to 16 years.

Source: The New England Journal of Medicine. 2019 Dec 5;381(23):2209-2218.