Abstract
Background: Case-control studies have not been examined for their utility in assessing population-level vaccine protection in individually randomized trials. Methods: We used the data of a randomized, placebo-controlled trial of a cholera vaccine to compare the results of case-control analyses with those of cohort analyses. Cases of cholera were selected from the trial population followed for three years following dosing. For each case, we selected 4 age-matched controls who had not developed cholera. For each case and control, GIS was used to calculate vaccine coverage of individuals in a surrounding "virtual" cluster. Specific selection strategies were used to evaluate the vaccine protective effects. Results: 66,900 out of 108,389 individuals received two doses of the assigned regimen. For direct protection among subjects in low vaccine coverage clusters, we observed 78% (95% CI: 47-91%) protection in a cohort analysis and 84% (95% CI: 60-94%) in case-control analysis after adjusting for confounding factors. Using our GIS-based approach, estimated indirect protection was 52% (95% CI: 10-74%) in cohort and 76% (95% CI: 47-89%) in case control analysis. Estimates of total and overall effectiveness were similar for cohort and case-control analyses. Conclusion: The findings show that case-control analyses of individually randomized vaccine trials may be used to evaluate direct as well as population-level vaccine protection.
Original language | English (US) |
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Pages (from-to) | 6878-6883 |
Number of pages | 6 |
Journal | Vaccine |
Volume | 33 |
Issue number | 48 |
DOIs | |
State | Published - Nov 27 2015 |
Keywords
- Case-control study
- Cohort study
- Herd effect
- Randomized controlled trial
- Vaccine effectiveness
ASJC Scopus subject areas
- Molecular Medicine
- General Immunology and Microbiology
- General Veterinary
- Public Health, Environmental and Occupational Health
- Infectious Diseases