Various field studies has found that the modified , bivalent, whole cell - based oral cholera vaccine (OCV) to be safe, immunogenic and effective with protective efficacy of 67 % in earlier clinical trials. However, the effectiveness of the vaccine in "real" life situation using the public health system is unknown. It is critical to follow up in the same population, where pilot introduction of OCV was introduced and evaluate vaccine proactive effectiveness at individual as well as at population level. The follow - up and determination of effectiveness of mass OCV vaccination was requested by State Government.
The overall goal of this study is to evaluate the protective effectiveness of one or two doses of modified, bivalent, killed whole cell based OCV, given at least 14 days apart, when delivered through community - based mass vaccination campaign using existing public health infrastructure in a high - risk population in Satyabadi block of Puri district, Orissa, India. This study has following objectives Primary objectives: \* To evaluate the individual level protective effectiveness of one or two doses of OCV against culture confirmed cholera episodes, severe enough to seek a formal health care. Secondary objectives: * To evaluate population - level effectiveness (herd effects)of OCV delivered through a community based mass vaccination when the vaccine is delivered to more than half of population at risk. * To determine inverse correlation between vaccine coverage and cholera incidence among diverse geographical clusters.
Study Type
OBSERVATIONAL
Enrollment
240
Regional Medical Research Center
Chandrashekharpur, Bhubaneswar, Odisha, India
RECRUITINGVaccine protective effectiveness at individual level
Matched controls will be selected among the persons of the same age group as that of each case. 1 to 4 ratio will be used in matching cases to controls.Information on all other exposure variables will be collected through questionaire interview for both cases and controls."Protective effectiveness (PE) (%) = \[1- the odds of vaccination among cholera confirmed cases relative to the odds of vaccination among matched controls\] × 100" is the metric to measure vaccine protective effectiveness at individual level.
Time frame: 11 months
Population level effectiveness (herd effect)
Indirect effect: Fraction of household members who are vaccinated in households of unvaccinated cases compared with fraction of household members who are vaccinated in households of unvaccinated controls Total effect: Fraction of household members who are vaccinated in households of vaccinated cases compared with the fraction of household members who are vaccinated in households of vaccinated controls. Overall effects: Fraction of household members who are vaccinated in household of cases compared with fraction of household members who are vaccinated in control households.
Time frame: 11 months
Cohort / GIS study for the measure of herd protection
Geographic unit as a cluster for evaluating vaccine herd protection with the use of cohort analysis, using GIS information from the baseline census. Here, there will be comparison in the incidence of the target outcome (cholera or non-cholera diarrhea) according to the level of vaccine coverage of the geographic unit.
Time frame: 11 months
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