BACKGROUND: An Australian study including 4433 children found that delayed Diphtheria-Tetanus-acellular Pertussis containing vaccination was associated with reduced risk of developing atopic dermatitis (AD) before 1 year of age. OBJECTI: ve We assessed if delayed vaccination against diphtheria, tetanus, acellular pertussis, polio, and Haemophilus Influenzae type b (DTaP) was associated with a reduced risk of new cases of AD before 1 year of age in Denmark.

METHOD: s We used nationwide registers to follow 883,160 children born in Denmark from 1997 to 2012. Binary regression models adjusting for potential confounding factors were applied to estimate relative risks (aRR) of developing AD among children with delayed DTaP vaccination (defined as given 1 month or more after the recommended age) compared with timely vaccinated children.

RESULTS: Among 143,429 children with a delayed first dose of DTaP, 4847 (3.4%) developed AD between 4 months and 1 year of age, compared with 27,628 (3.7%) among 739,731 children not having delayed DTaP (aRR 0.94 (95% confidence interval (CI): 0.91-0.97)). The aRR was 0.94 (95% CI: 0.90-0.99) for children with a delayed second dose, and aRR=0.88 (95% CI: 0.2-0.93) comparing children with delayed first and second dose with all timely vaccinated children.

CONCLUSION: The results support the hypothesis that delayed vaccination with DTaP is associated with reduced risk of developing new cases of AD after 4 months of age. The dose-dependent relationship strengthens the evidence of a causal relationship. Some countries are introducing maternal pertussis vaccination and delaying the first dose of DTaP, providing a possibility for further testing the hypothesis.