A Cluster-Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy of Vitamin D3 Supplementation to Reduce Disease Severity in Persons With Newly Diagnosed COVID-19 Infection and to Prevent Infection in Household Members

Data from laboratory studies, epidemiologic research, and randomized clinical trials conducted in the pre-COVID era strongly suggest that vitamin D is active in pathways relevant to immune function and may reduce the risk of acute respiratory infections. More recently, some observational studies have shown a significant association between low vitamin D status and worse clinical outcomes among COVID-19 patients. Whether vitamin D supplementation can reduce the risk of adverse clinical outcomes in recently diagnosed COVID-19 patients and/or reduce risk of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV- 2) in those likely to have been exposed to the virus (post-exposure prophylaxis) is unknown.

The Vitamin D for COVID-19 Trial (VIVID) is a pragmatic, cluster-randomized clinical trial in 2024 men and women recruited nationwide from the U.S. and Mongolia. The trial is investigating whether taking a daily dietary supplement of vitamin D3 vs. placebo for 4 weeks reduces the rate of seeking healthcare visits (including hospitalizations, emergency room visits, or ambulatory or virtual clinician visits) for symptoms or concerns related to COVID-19 or deaths in people newly diagnosed with COVID-19, and reduces the risk of SARS-CoV-2 infection in household contacts of individuals with newly diagnosed COVID-19.

The trial has enrolled 1747 individuals aged 18 or older who are newly diagnosed with COVID-19 ("index cases") and 277 household contacts aged 18 or older.

Following receipt of informed consent, participants are randomized -- i.e., assigned by chance (like a coin toss) -- to one of two groups: (1) daily vitamin D3 (9600 IU/day on days 1-2; 3200 IU/day on days 3-28) or (2) daily vitamin D placebo. Index cases and household contacts of an index case (limited to at most one contact per household), if any, are assigned to the same group (cluster randomization). Participants take three oral softgel capsules on day 1, three capsules on day 2, and one capsule each day on days 3 through 28. Participants receive a 4-week supply of study capsules via overnight courier service.

Participants fill out a short (15-20 minute) questionnaire each week during the 4-week pill-taking period, as well as a follow-up questionnaire at 8 weeks after randomization. These questionnaires ask about symptoms, general health, and use of medications and dietary supplements. Questionnaires are completed online using a secure Internet-based system known as the Research Electronic Data Capture (REDCap) system. Participants must have an e-mail address to enroll in the study. Occasionally, participants (or their delegates) may receive a telephone call from study staff to collect information or to clarify answers on the questionnaire. Participants may contact investigators or staff using a toll-free number, if they have any questions or need assistance.