Association between vitamin D deficiency and clinical outcome in patients with COVID-19 in the post-Omicron phase.

Background: Vitamin D deficiency (VDD) has been associated with adverse outcomes in COVID-19 patients during the early pandemic phases, but whether this association persists in the post-Omicron era remains uncertain. This study aimed to investigate the evolving relationship between VDD and COVID-19 outcomes across pandemic phases using a large healthcare database. Methods: We conducted a retrospective cohort study using the TriNetX Analytics Network, analyzing propensity-matched cohorts comprising 24,236 pairs from the post-Omicron phase (June 2022-December 2023) and 22,638 pairs from the pre-Omicron phase (January 2020-December 2021). VDD was defined as a serum 25-hydroxyvitamin D level < 20 ng/ml, with vitamin D-sufficient patients (≥30 ng/ml) serving as controls. The primary outcome was 30-day all-cause mortality, with secondary outcomes including acute kidney injury, respiratory failure, pneumonia, sepsis, and ICU admission. Results: The 30-day mortality in VDD vs. vitamin D-sufficient patients decreased from 1.43% vs. 0.39% [odds ratio (OR), 3.67; 95% CI, 2.90-4.64; Conclusion: VDD continues to be associated with adverse COVID-19 outcomes in the post-Omicron phase, albeit with a reduced magnitude. These findings support the importance of vitamin D screening in high-risk COVID-19 patients, while emphasizing the need for adaptive risk assessment strategies that incorporate both established and emerging risk factors in the current pandemic landscape.