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Assessing different measures of population-level vaccine protection using a case-control study

Mohammad, Ali, You, Ae You, Kanungo, Suman, Manna, Byomkesh, Deen, Jacqueline L., Lopez, Anna L., Wierzba, Thomas F., Bhattacharya, Sujit K., Sur, Dipika and Clemens, John D. (2015). Assessing different measures of population-level vaccine protection using a case-control study. Vaccine,33(48):6878-6883.

Document type: Journal Article
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IRMA ID 81144320xPUB109
Title Assessing different measures of population-level vaccine protection using a case-control study
Author Mohammad, Ali
You, Ae You
Kanungo, Suman
Manna, Byomkesh
Deen, Jacqueline L.
Lopez, Anna L.
Wierzba, Thomas F.
Bhattacharya, Sujit K.
Sur, Dipika
Clemens, John D.
Journal Name Vaccine
Publication Date 2015
Volume Number 33
Issue Number 48
ISSN 0264-410X   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-84951568859
Start Page 6878
End Page 6883
Total Pages 6
Place of Publication United Kingdom
Publisher Elsevier Ltd
HERDC Category C1 - Journal Article (DIISR)
Abstract Background

Case–control studies have not been examined for their utility in assessing population-level vaccine protection in individually randomized trials.


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.


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.


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.
Keywords Vaccine effectivness
Herd effect
Case-control study
Cohort study
Randomized controlled trial
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