Introduction: In March 2020, less than three months after China reported a cluster of pneumonia cases in Wuhan, the United States (US) government budgeted money to support development of Covid-19 vaccines. By mid-December 2020, two had been developed, tested, and received the US government’s experimental use authorization. Given evidence that vitamin D supplements and live vaccines for tuberculosis, polio, and measles reduce risks for acute respiratory infection, many experts hypothesized they might reduce risks for Covid-19 infection. Expedited randomized controlled trials, as done for Covid-19 vaccines, could have assessed their protection against C19 no later than end-July 2020. Methods: On 21 April 2021, I searched trial registries maintained by the US National Institutes of Medicine and the World Health Organization for trials with ≥400 participants to assess vitamin D or live vaccines to prevent Covid-19 infections (all or symptomatic). On 10-13 November 2021, I searched PubMed and medRxiv for results reported from these trials.Results: In April 2021, I found 32 trials (9 for vitamin D and 23 for live vaccines) proposing to assess the impact of these interventions on rates of new Covid-19 infections (all or symptomatic). Only 10 trials proposed to begin by June 2020, and only one to end in 2020. My search on 10-13 November 2021, almost 11 months after the US approved the first two Covid-19 vaccines, found results reported from only one of the 32 trials (live measles vaccine significantly reduced new symptomatic infections). Conclusions: If health experts had demonstrated similar urgency in assessing vitamin D supplements and live vaccines for tuberculosis, polio, and measles as in developing Covid-19 vaccines, trials could have reported by end-July 2020. Depending on what trials reported, these interventions could have prevented a large percentage of more than 600,000 Covid-19 deaths reported in the US from August 2020 through November 2021. Delay in assessing vitamin D has racial implications as well, since vitamin D deficiency and Covid-19 deaths in the US have been far more common among Blacks and Hispanics compared to Whites. Going forward, depending on what trials report, these interventions could help people live with Covid-19 as an endemic virus.