Eficacia protectora de las vacunas y efectividad de las vacunaciones: Introducción a la medición de la protección directa e indirecta

We define the concepts of protective vaccine efficacy (the protective value of a vaccine applied in ideal conditions) and vaccination effectiveness (the protective value of a vaccination applied in routine clinical practice or public health programs), and describe the methods of evaluating these two parameters. Protective efficacy is always evaluated by experimental studies (controlled clinical trials and randomized community trials). Vaccination effectiveness is evaluated by observational epidemiological studies (normally cohort and case-control studies). Controlled clinical trials and case-control and cohort studies only measure the direct protection conferred by the vaccine or vaccination. To evaluate indirect protection, community-based cluster randomized trials (population groups) or descriptive population-based studies that evaluate the impact of vaccination programs are required.