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https://doi.org/10.1016/j.eclinm.2018.11.004 2589-5370/© 2018 Published by Elsevier Ltd. T Vaccination against infectious diseases is of the utmost importance They start later with the vaccination program if they immunize their for the health of our children. Therefore, it is good that the vaccination coverage today is extensive, e.g. estimated at 86% for children globally for vaccination against diphtheria, tetanus and pertussis vaccination [1]. The age when these vaccine doses are administered differs between countries, but the first doses are normally given between 6 weeks and 3 months of age. Besides the risk of infection, does the age of the infant at the first immunization have any other consequences for the health of the child? It has been proposed that there could be a shift in the T-helper cell type 1/T-helper cell type 2/regulatory T cells balance and that more allergic diseases will develop with early vaccination in infancy. Previous studies have been contradictory with respect to the association of immunization at an early age with the development of allergic diseases. Kiraly et al. [2] found no association with the first vaccine doses (DTaP and invariably Hep B, Hib, PCV, rotavirus) at around 2 months vs N3 months for food allergy or atopic sensitization. There was, however, an increase in eczema at one year of age. MacDonald et al. found a negative association between delay in administration of the first dose of whole-cell pertussis vaccine in DPT immunization in childhood and the development of asthma; the association was greater with delays in all of the first 3 doses [3]. This Canadian study used retrospective data, which might have led to selection bias. However, Grüber et al. [4] showed in children at heightened risk of atopy that common childhood immunization in the first year was not associatedwith an increased risk of more severe eczema or allergic sensitization. They recommended that parents of atopic children should be encouraged to fully immunize their children. After 14 years of no general pertussis vaccination, almost 82,000 Swedish children were immunized for pertussis in a vaccination trial [5]. Data for the main outcome variable (i.e., dispensed prescribed asthma medication for each individual in the cohort during