Vaccine is a biological preparation which provides an immunity and helps in prevention of diseases. Though it can be considered as an important factor to children because the children are more prone to disease, Vaccines are widely considered one of the greatest achievements in public health having had a dramatic impact on the prevalence of several infectious diseases including smallpox, poliomyelitis, and measles. However it has been prepared it should have its own safety and efficacy till the entire shelf life of the product. Clinical trials have become critical for evaluating new vaccines as well as other prevention and treatment strategies in combating human diseases. Today the randomized, controlled trial is the gold standard for providing scientific evidence regarding the efficacy of a candidate vaccine. Program evaluation is essential to understand the success and challenge associated with the implementation of a vaccination program and the impact of the program on disease burden. The purpose of evaluating immunization programs is to measure progress made toward predetermined objectives.