Influenza-like illness and covid-19 were added to this summary because the protocol uses respiratory tract infections and influenza-like illness interchangeably. Influenza-like illness is more accurate.~Protocol amendments:~Protocol title was amended to include covid-19. Minimum age was changed from 52 to 18, expanding the sample size. Exclusion criteria re vitamin D intake was changed from >5000 to >=5000 IU.
The Cooper vitamin D3 study is a randomized study investigating whether daily vitamin D3 supplementation can prevent respiratory tract infections, influenza-like illness and covid-19 in hospital workers.