The relationship between serum vitamin D and antibody response following two doses of inactivated COVID-19 vaccine

Objectives Low vitamin D levels are associated with the severity and mortality of COVID-19 infection. Nevertheless, the relationship between the 25-hydroxyvitamin D [25(OH)D] levels and the antibody response following COVID-19 vaccination is not fully elucidated. Herein, we explored the relationship between SARS-CoV-2 IgG (sCOVG) and 25(OH)D. Methods In this prospective observational case-control study, we used an automated chemiluminescent immunoassay method to measure sCOVG and 25(OH)D levels in 96 patients 28 days following the second dose of inactivated vaccine. We considered the positivity for sCOVG at three different index values: 1, 2.42, and 7. We classified 25(OH)D levels between 0 and 20 ng/mL as vitamin D deficiency, 21-29 ng/mL as insufficiency and 30 ng/mL as sufficiency. Results Median sCOVG index was 6.02 (interquartile ranges 3.41-11.63) and median 25(OH)D level was 11.5 ng/mL (interquartile ranges 10-17). We could not find a significant correlation between 25(OH)D and sCOVG levels (Spearman's rho, r=0.175, p=0.12). When considering the variables categorically, we did also not conclude significant relationships between adequate or inadequate antibody responses in patients with deficient, insufficient, and sufficient 25(OH)D by three sCOVG cut-off index values (1, 2.42, and 7) (Chi-square test, p=0.8, 0.29, and 0.08, respectively). Conclusions The relevant literature is limited on the association between the antibody response to COVID-19 vaccines and vitamin D levels. Although the previous research suggested conflicting findings of the response to mRNA vaccines, we could not conclude a significant relationship between sCOVG and 25(OH)D levels 28 days after two doses of inactivated COVID-19 vaccine.