On measures and models for the effectiveness of vaccines and vaccination programmes.

Smith, Rodrigues and Fine have discussed and linked different measures, models, and study designs for the assessment of vaccines. The present paper responds to a number of issues implicitly raised by these authors. In particular, it is argued that measures and models need to be considered independently, with choice of measure depending on evaluation objectives, and choice of model depending on consideration of both mechanism of administration and mechanism of action. Models in which a particular measure remains constant tend to be unrealistic for evaluating field effectiveness. Some technical issues arising in the design and analysis of case-control studies of vaccines are also addressed.