Effectiveness of the TYPHIBEV® (Vi-CRM197 conjugate) vaccine introduction in Nepal: a test-negative, case-control study
Bibliographic record
Abstract
ABSTRACT Introduction Typhoid fever, caused by Salmonella Typhi, remains a major cause of global morbidity and mortality. TYPHIBEV®, a Vi-CRM197 typhoid conjugate vaccine (TCV), received WHO prequalification based on immunogenicity data, but there have been no published data on clinical efficacy or effectiveness. We aimed to evaluate the effectiveness of TYPHIBEV®, which was introduced through a catch-up campaign and routine immunization in Nepal, in preventing blood culture-confirmed typhoid fever among children. Methods We conducted a test-negative, case-control study where typhoid test-positive cases were defined as vaccine-eligible pediatric patients who tested positive for Salmonella Typhi by blood culture at participating health facilities and test-negative controls were vaccine-eligible patients who tested negative for S . Typhi on blood cultures. We matched by age, location, date of blood culture, and surveillance site. We used conditional logistic regression to calculate odds ratios (OR), and vaccine effectiveness was calculated as 1-OR. Results Between October 1, 2022 and December 31, 2024, 40 typhoid cases and 113 matched, test-negative controls were enrolled. Both cases and controls were similar in sociodemographic characteristics and water, sanitation and hygiene-related living conditions. Among 39 cases and 108 controls with known vaccine status, 20 cases (51%) and 91 controls (84%) had received TCV. Vaccine effectiveness was 89% (95% CI: 65-97%) and was lower among children <5 years (72%, 95% CI: -203-97%) compared with those 5-15 years (98%, 95% CI: 80-100%). Vaccine effectiveness estimates did not significantly differ when restricted to participants with documented vaccination status. Conclusion The findings indicate that TYPHIBEV® was highly effective in preventing typhoid fever up to 30 months following a national introduction, with effectiveness estimates comparable to those observed for Typbar-TCV®.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.005 |
| Meta-epidemiology (narrow) | 0.000 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".