Up to 50% of children suffer from acute wheezing before school-age. The prevalence of childhood asthma is 5-7%. Although pediatric asthma is mainly allergic, the exacerbations are associated with respiratory viral infections in 95% of cases. The means to predict asthma from environmental factors have been limited mainly to sensitization to aeroallergens (3-fold risk), which start to develop usually at 2-3 years of age. VINKU 1-study (orig. VINKU-study) discovered simultaneously with two other groups, that early wheezing associated with rhinovirus, the "common cold" virus, is the strongest predictor of recurrent wheezing/asthma (up to 10-fold risky). Noteworthily, viral infections work as risk markers already during infancy, a lot earlier than the sensitization to aeroallergens. The investigators also found retrospectively that early wheezers affected by rhinovirus responded to 3 day course of oral prednisolone (inexpensive and widely available treatment): recurrent wheezing decreased by 50% during following 12 months and the difference appeared to continue. VINKU 5V-study is currently investigating the clinical history, prevalence of asthma and airway hyperreactivity of these same children at school-age. The mechanism of rhinovirus associated risk or why they respond to prednisolone are largely unknown. However, the susceptibility to rhinovirus infections is associated with atopy and therefore it is possible these children may have impaired anti-inflammatory (Treg) responses and more likely to wheeze with any pro-inflammatory response (Th1 or Th2). Moreover, they may not effectively clear viruses, because they can not limit rhinovirus to nose and it spreads to lower airways and causes wheezing. VINKU 2-study will prospectively investigate the immunological events in young first-time wheezers affected by rhinovirus, and prospectively study the clinical efficacy of systemic corticosteroid in them. Most likely these children will benefit from the drug in terms of less recurrent wheezing, the investigators will also explore immunological effects of the drug and their link to clinical efficacy. The results are expected to give basis for the prevention of asthma and for the development of new treatment strategies and they can be directly applied to clinical medicine.