Efficacy and Safety of Vitamin D Supplementation to Prevent COVID-19 in Frontline Healthcare Workers. A Randomized Clinical Trial
et al., Archives of Medical Research,
RCT 321 healthcare workers in Mexico, showing significantly lower SARS-CoV-2 infection with vitamin D prophylaxis. 4,000IU daily for 30 days.
In comparison to [Jolliffe]
, this study used a higher dose, the participants had much higher exposure to SARS-CoV-2 patients, and the study was prior to vaccination. In [Jolliffe]
, 89% of participants had received a vaccine dose by the end of the study period, and the period overlapped with increasing solar UVB.
For more discussion see 
risk of hospitalization, 66.5% lower, RR 0.33, p = 1.00, treatment 0 of 150 (0.0%), control 1 of 152 (0.7%), NNT 152, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm), ITT.
risk of case, 78.0% lower, RR 0.22, p = 0.001, treatment 7 of 150 (4.7%), control 26 of 152 (17.1%), NNT 8.0, adjusted per study, multivariable, Table 3.
Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
Villasis-Keever et al., 18 Apr 2022, Double Blind Randomized Controlled Trial, placebo-controlled, Mexico, peer-reviewed, 16 authors, study period 15 July, 2020 - 30 December, 2020, dosage 4,000IU daily.