Non-specific effects of vaccination: Authors' reply to Aaby et al

doi:10.1136/bmj.330.7495.845

BMJ 2005;330:845 (9 April), doi:10.1136/bmj.330.7495.845

Letter

Non-specific effects of vaccination

Authors' reply to Aaby et al

The first 150 words of the full text of this article appear below.

EDITOR—Aaby et al raise issues of general rather thanspecific interest, as their references indicate. The study ofthe effects of vaccines, which pioneered the randomised controlledtrials method more than 50 years ago, is still topical and ofgeneral interest.¹ The limitations discussed by Aaby et al areintrinsic to all observational datasets and, in this respect,the assets of our study are to rely on both independent andshared pre-planned analyses² of observational datasets, issuedfrom a country other than Guinea-Bissau. The simulations weperformed (which are available on request) on the effects ofa possible survival bias logically influenced our estimatestowards 1 but did not yield different conclusions.

In addition to the misclassification aspect, causal inferenceis also an issue at stake. In this respect, we agree with Finethat the conclusion of our study is no evidence for a positiveassociation between any . . . [Full text of this article]

J Vaugelade, demographer

vaugelad@ird.fr, Institut de Recherche pour le Développement, Laboratoire Population, Environnement et Développement, BP 64501, 34394 Montpellier Cedex 5, France

F Simondon, epidemiologist, E Elguero, statistician

Institut de Recherche pour le Développement, Laboratoire Population, Environnement et Développement, BP 64501, 34394 Montpellier Cedex 5, France

S Pinchinat, biostatistician

Biostatem, Parc Scientifique G Besse, F 30035 Nîmes, France

G Guiella, researcher

Unité d'Etudes et de Recherche en Démographie, 03 BP 7118, Ouagadougou 03, Burkina Faso