Lack of Vitamin D Predicts Impaired Long-term Immune Response to COVID-19 Vaccination

Purpose: Low vitamin D levels were reported to negatively influence the outcome of acute COVID-19, as well as to be linked to Long-COVID. However, few studies have investigated, so far, its effects on humoral-response to anti-SARS-CoV-2 vaccination, reporting conflicting results. We aimed to evaluate the impact of baseline 25(OH)vitamin D (25(OH)D) levels on humoral-response to a two-dose cycle of Pfizer-BioNTech-vaccine up to 9-10 months after immunization.

Methods: We retrospectively included 119 consecutive healthcare-workers (median age 53 years) without a previous history of acute COVID-19 or anti-SARS-CoV-2 immunoglobulins presence immunized with two doses of Comirnaty-vaccine from January to February 2021. 25(OH)D was measured at time of first-immunization. Immune response was evaluated at: time 0 (T0), before the first-dose; T1, time of second-dose (21 days after T0); T2, T3, T4 at 1, 5 and 9 months after T1, respectively.

Results: Median 25(OH)D levels were 25.6 ng/mL, and vitamin D deficiency (25(OH)D <20 ng/mL) was observed in 29 subjects (24.8%). In those with vitamin D deficiency, we found a non-significant trend towards lower antibody-titers at T3, and significantly lower titers at T4 as compared to those not vitamin D-deficient, also observing a more pronounced antibody-titers negative drop from peak-T2 and T4 in those with vitamin D deficiency. A positive correlation between 25(OH)D levels and antibody-titers at T4 (p = 0.043) was found. In multiple linear-regression analysis, 25(OH)D deficiency and older-age resulted as negative independent factors associated with antibody titer at T4 (p = 0.026, p = 0.004; respectively).

Conclusion: In our relatively young cohort presenting low prevalence of hypovitaminosis D, the long-term humoral response to anti-SARS-CoV-2 vaccination was negatively influenced by low baseline 25(OH)D. Vitamin D supplementation could be tested as a strategy to optimize the vaccination campaigns to prevent severe COVID-19.