Associations between pre-infection serum vitamin D concentrations and Omicron COVID-19 incidence, severity and reoccurrence in elderly individuals.

Objective: Previous studies suggest a link between vitamin D status and COVID-19 susceptibility in hospitalised patients. This study aimed to investigate whether vitamin D concentrations in elderly individuals were associated with their susceptibility to Omicron COVID-19 incidence, the severity of the disease and the likelihood of reoccurrence during the era of the post-'zero-COVID-19' policies in China.

Design: In this retrospective study, participants were categorised into three groups based on their 25(OH)D concentrations: deficiency (< 20 ng/ml), insufficiency (20 to < 30 ng/ml) and sufficiency (≥ 30 ng/ml). The demographic and clinical characteristics, comorbidities and the incidence rate, reoccurrence rate and severity of Omicron COVID-19 were retrospectively recorded and analysed by using hospital information system data and an online questionnaire survey.

Setting: China.

Participants: 222 participants aged 60 years or older from a health management centre.

Results: Our findings revealed significant differences in the incidence (P = 0·03) and recurrent rate (P = 0·02) of Omicron COVID-19 among the three groups. Participants with lower 25(OH)D concentrations (< 20 ng/ml) exhibited higher rates of initial incidence and reoccurrence and a greater percentage of severe and critical cases. Conversely, individuals with 25(OH)D concentrations ≥ 30 ng/ml had a higher percentage of mild cases (P = 0·003). Binary and ordinal logistic regression models indicated that vitamin D supplementation was not a significant risk factor for COVID-19 outcomes.

Conclusions: In the elderly population, pre-infection vitamin D deficiency was associated with increased susceptibility to incidence, severity of illness and reoccurrence rates of Omicron COVID-19.