B-145 Longitudinal Post-Immunization Serological Study of COVID-19. Potential influence of Vitamin D on antibody response

Abstract

Serological testing plays a critical role in identifying SARS CoV 2 infection and monitoring immune responses to vaccination. COVID 19 mRNA vaccines, including BNT162b2, reliably elicit antibodies targeting the receptor-binding domain of the viral spike protein. However, the durability and magnitude of antibody responses following the first vaccine dose, particularly beyond four weeks, is not well defined. Understanding early and long term antibody responses post vaccination is especially important in the context of delayed second dose strategies aimed at optimizing vaccine distribution. In parallel, vitamin D has been implicated in immune modulation, but the relationship between vitamin D status and vaccine induced immunity remains unclear. The CALM (COVID Antibody Longitudinal Monitoring) study was undertaken to characterize long term antibody response and assess the relationship with vitamin D levels. A total of 110 healthcare workers at a large university hospital in Norwich, UK were enrolled in a prospective cohort study and followed for 68 weeks from January 2021 to July 2022. Participants received two doses of BNT162b2 followed by a booster dose. Blood samples were collected from baseline through 18 months, including post dose 1 (week 1), post dose 2 (week 12), and post booster time points. SARS CoV 2 anti spike IgG (quantitative IgG II) levels were measured using the Abbott Alinity i instrument. Vitamin D metabolites (25OHD) were quantified using LC MS/MS. Participants were categorized as vitamin D deficient, insufficient, or replete at baseline, and changes in levels following supplementation were documented. Distinct multiphasic IgG peaks were observed after the first dose, second dose, and booster, reflecting expected priming dynamics. Most participants exhibited a high antibody response (“normal responders”), whereas three participants demonstrated consistently minimal or delayed responses throughout the 18 month period. After the second dose, the gap between normal and poor responders narrowed but did not fully resolve. A high baseline IgG level did not predict enhanced responsiveness to subsequent vaccine doses. At baseline, 24.3% of participants were vitamin D deficient and 39.6% were replete. Vitamin D deficiency was associated with reduced early IgG responses following the initial- vaccine dose. After approximately four weeks of self-supplementation of vitamin D initiated during the study, mean 25OHD levels increased by 30.9 nmol/L. By week 12, only 2.9% of participants remained deficient and 83.5% were replete. Antibody responses converged by week 12, consistent with both the correction of a deficiency and the robust secondary immune response elicited by the priming dose. Vitamin D status had a stronger influence on the initial vaccine dose response than on the later 2nd or boosted response. The Abbott Alinity i IgG II Quant assay provides an effective tool for population level monitoring of post vaccination immunity. This longitudinal study demonstrates that adequate vitamin D status is associated with stronger early humoral responses to the first COVID 19 vaccine dose. Although antibody levels converged following the second dose, these findings may support a potential role for vitamin D in modulating early immune responsiveness and possibly influencing disease susceptibility.