- Delayed diagnosis; Atopic dermatitis does not become apparent until the child has scratched the affected skin. Furthermore, it may take weeks to months before the parents become aware that this is not something which is passing, and bring the child to a doctor. Therefore, it is very likely that actual onset of AD is weeks/months prior to date of diagnosis by the healthcare professionals or receipt of disease specific prescriptions. Due to this delay, there is a risk of differential misclassification, whereby cases of AD may be falsely ascribed to the vaccinated exposure group. A sensitivity analysis will account for this delay by setting the date for onset of AD prior to onset according to the AD algorithm. Primary health care facilities will be contacted in order to gain expert insight on approximate delay from onset of symptoms to receipt of prescription medicines or referral to a hospital.