PREDICTING THE ACCRUAL RATE IN A VACCINE CLINICAL-TRIAL - AN A-POSTERIORI EVALUATION OF THE FEASIBILITY STUDY

To estimate the expected accrual rate in a double blinded controlled r andomized trial of the absolute clinical efficacy of three anti-pertus sis vaccines in infants, we performed a series of surveys among mother s and physicians in the areas to be considered for participation in th e trial. In this paper, we compared the predicted enrollment with the actual enrollment achieved at the end of the recruitment phase of the trial. The predicted enrollment rate was 27 %, while the observed rate was 26 %. Results from the feasibility study were highly predictive o f actual enrollment rate. In the local health units (USL) where such a ssessments were carried out, the accrual rate was higher than those no t participating in the feasibility phase.