The investigators will recruit 160 infants who require oxygen therapy (oxygen saturation <92%) during hospitalization due to a viral bronchiolitis. The participants are randomized to receive oxygen therapy either with high flow or ordinary nasal cannula.The infants are closely observed by study physicians for clinical parameters. The primary end point is treatment failure (need for change of respiratory support method). Secondary endpoints are respiratory rate (RR) and oxygen saturation (%) at specific measuring points, time from randomisation to end of oxygen therapy and time from randomisation to discharge.