In children aged 1–24 months hospitalised with bronchiolitis at Teaching Hospital Jaffna, does high-dose oral vitamin D supplementation, compared with placebo, improve clinical severity as measured by the Modified Tal Score at 24, 48, and 72 hours after recruitment?”

Study setting - Teaching Hospital Jaffna

Randomization Participants. will be allocated by simple randomization. Participants will be randomly assigned in a 1:1 ratio to either the intervention group or the control group using a computer-generated randomization sequence.

Following informed consent, a sealed opaque envelope containing the allocation code (either (A or B) will be opened, and the assigned study medication will be administered.

Intervention arm The infants in the interventional arm will receive the oral vitamin D Supplementation (infant drop form) 100 IU/Kg/Day or 1000 IU / day – whichever is minimal once daily from day 1 of admission for 7 days (Vitamin D drops with the strength of 400 IU per drop will be used and the volume of the vitamin D will be calculated according to the bodyweight of the infants. 1ml oral syringe will be used to administer the vitamin D).

Control arm Infants in the control arm will receive oral normal saline drop (0.9% NaCl) as placebo liquid in the amount like the vitamin D once daily from day 1 of admission till for 7 days. Volume of saline will be calculated as same as vitamin according to the body weight and administered using 1 ml oral syringe.

If the babies are discharged earlier, they will be requested to follow up daily till day 7 in the ward and the intervention will be continued and the travel costs will be reimbursed. This information will be incorporated in the information sheet.

Standard care will be provided to both arms in accordance with National Guideline on Bronchiolitis issued by the Sri Lanka College of Paediatricians. The standard care includes - Oxygen therapy if saturation is <92% either through nasal prong or heated humidified high flow nasal cannula - fluid and nutrition – small frequent feeds if tolerated or Ng feeds or IV fluids - nasal suctioning/saline if upper airway obstruction is present.

Blinding: Double blinded Both the vitamin D and normal saline placebo preparations will be provided as identical oral drop formulations in indistinguishable containers. The normal saline placebo will be packaged in a container identical to that used for the vitamin D preparation. The outer surfaces of both containers will be completely masked with identical coverings and labelled only as "A" or "B", without revealing their contents.

Packaging and labelling of the study preparations will be carried out by an investigator who is not involved in participant recruitment, clinical management, outcome assessment, or data analysis. The allocation code linking the labels ("A" and "B") to the respective study preparations will be securely maintained in a sealed envelope and will remain concealed until completion of data analysis, thereby ensuring maintenance of blinding throughout the study.

A designated member of the research team, who is not involved in outcome assessment, will administer the assigned study preparation (oral vitamin D or placebo) to the infants once daily in the morning under the supervision of the nursing officers. The formulation of vitamin D used is clear and colourless, although oily in appearance. Both the interventional product and the placebo will be administered using a 1ml syringe with clear 0.1ml markings. The study preparations will be administered throughout the infant's hospital stay or until the seventh day of hospital admission, whichever is longer. This procedure will ensure that the study preparation is not accessible to parents or other ward staff, thereby maintaining blinding. Direct administration by the research team will ensure that the correct study preparation is given to each participant and will facilitate monitoring of treatment compliance.

1. Male and female infants aged 4 weeks to 24 months hospitalized with symptoms of bronchiolitis, defined as signs and symptoms of respiratory distress associated with symptoms of a viral respiratory tract infection.
2. Infants who are stable on room air or on nasal prong oxygen < 2 L/minute
3. Pulse rate <180beats/min
4. Respiratory rate <80 breaths/min

1. Infants admitted directly to ICU
2. Infants needing heated humidified high flow oxygen
3. Infants with other co-morbidities like congenital heart disease, neuromuscular anomalies, immune deficiency, chronic lung disease.
4. Extreme prematurity
5. Infants receiving vitamin D within 4 weeks preceding the study period.