Trial of Vitamin D Supplementation for the Prevention of Influenza and Other Respiratory Infections (ViDiFlu)

Inclusion Criteria:

• Permanent resident or member of staff at sheltered accommodation unit
• If a woman of child-bearing potential, is sexually abstinent or has negative pregnancy test within 7 days of recruitment and agrees to use reliable form of contraception until she has completed the study
• Able to give written informed consent to participate
• Age ≥ 16 years on day of first dose of IMP

Exclusion Criteria:

• Current diagnosis of asthma or chronic obstructive pulmonary disease
• Chronic upper or lower respiratory infection or other condition causing chronic cough
• Condition requiring treatment with vitamin D at a dose of > 10 micrograms vitamin D/day
• Episode of upper or lower respiratory tract infection up to 28 days before first dose of IMP
• Known sarcoidosis, hyperparathyroidism, nephrolithiasis, active tuberculosis, vitamin D intolerance, liver failure, renal failure, terminal illness, lymphoma or other malignancy not in remission at time of recruitment
• Taking benzothiadiazine derivative, cardiac glycoside, carbamazepine, phenobarbital, phenytoin, primidone or long-term immunosuppressant therapy
• Taking oral preparation containing > 10 micrograms vitamin D/day up to 2 months before first dose of IMP
• Using topical vitamin D analogue
• Treatment with any investigational medical product or device up to 4 months before first dose of IMP
• Breastfeeding, pregnant or planning a pregnancy
• Baseline corrected serum calcium > 2.65 mmol/L
• Baseline serum creatinine > 125 micromol/L
• Inability to complete symptom diary with / without assistance
• Cognitive impairment or communication problem precluding informed consent or successful completion of study evaluations