No epidemiological evidence for infant vaccinations to cause allergic disease

Context: The prevalence of allergic diseases has increased considerably over the last decades. The hygiene hypothesis has emerged, linking reduced microbial exposure and infections early in life with the development of allergic diseases. Especially some of currently available non-replicating infant vaccines are unlikely to mimic a natural infection-mediated immune response that protects against the development of allergic diseases. Moreover, several studies suggested infant vaccinations to increase the risk of allergic diseases. Objective: To determine whether infant vaccinations increase the risk of developing allergic disease. Data. Sources: We searched MEDLINE from 1966 to March 2003 and bibliography lists from retrieved articles, and consulted experts in the field to identify all articles relating vaccination to allergy. Study Selection and Data Extraction: We selected epidemiological studies with original data on the correlation between vaccination with diphtheria, pertussis, tetanus (DPT), measles, mumps, rubella (MMR) and Bacillus Calmette-Guerin (BCG) vaccine in infancy and the development of allergic diseases, and assessed their quality and validity. Data Synthesis: Methodological design and quality varied considerably between the studies we reviewed. Many studies did not address possible confounders, such as the presence of lifestyle factors, leaving them prone to bias. The studies that offer the stronger evidence, including the only randomized controlled trial at issue published to date, indicate that the infant vaccinations we investigated do not increase the risk of developing allergic disease. Furthermore, BCG does not seem to reduce the risk of allergies. Conclusions: The reviewed epidemiological evidence indicates that, although possibly not contributing to optimal stimulation of the immune system in infancy, current infant vaccines do not cause allergic diseases. (C) 2004 Elsevier Ltd. All rights reserved.