Cálculo del tamaño de la muestra en los estudios epidemiológicos de evaluación de la efectividad vacunal

The effectiveness of a vaccination programme evaluates the results or health benefits provided to vaccinated subjects, when the vaccine is administered in normal clinical practise or public health programmes, which are far from optimal situations. Effectiveness is normally measured using observational studies. The number of subjects necessary for such studies is an important factor to consider in the initial stage of the study. This article reviews the criteria that should be taken into account when selecting study subjects and provides simple formulas to calculate the sample size of observational cohort or case-control studies.