A changing pattern of infections may be of importance for the increase in prevalence of asthma and other allergic diseases in developed countries during recent decades. The clear inverse relation between number of siblings and atopy observed in several studies may be related to a protective role of infections, although specific information is inconclusive. A recent study showed that positive tuberculin responses in schoolchildren correlated with a lower prevalence of atopic disorders, but other studies did not find a relation between BCG vaccination and allergic disease or sensitization. Transient production of IgE antibodies to pertussis toxin has been demonstrated after pertussis immunization; however, randomized clinical trials involving both whole cell and acellular pertussis vaccines have failed to show any enhancement of atopic manifestations in children. Epidemiologic investigations indicate that viral infections may either promote (RSV) or inhibit (hepatitis A, measles) atopy, although data are scarce. In conclusion, the evidence is limited regarding a direct role of vaccinations for development of atopic manifestations, but speaks against a major effect of some types of vaccinations. On the other hand, since some infections may offer protection in relation to allergy, vaccination could result in an increased risk.