Several public health interventions administer drugs and vaccines to large number of people for preemptive or reactive intervention. These vaccines and drugs were developed in very narrow conditions in clinical trials and we therefore have to continuously monitor the efficacy in the field. This paper proposes a method to evaluate the efficacy in the field using data collected from the intervention coverage survey and surveillance. The design is closely related to cohort prospective studies

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... t that the sample size is not fixed upfront and the measure of association not affected by the population denominator.It uses two new terms: hesitancy ratio denoted β, which is the ratio of the target that does to receive the intervention to the target that received it; event ratio is denoted by α is the ratio of health event or disease being prevented absolute incidence in the intervention group to that is in control group. It further shows that risk ratio (RR) can be calculated from these two parameters by taking their products. i.e. RR = α β. This method is therefore called Hesitancy and Event Ratios (HER) Method.We can conclude that this method is scientifically sound and can be used in the evaluation of public health intervention in the field. We recommend that this method be included in routine monitoring of programs for efficacy evaluation.