Immune Response After One Dose of Intramuscular Vaccination With the BNT162b2 mRNA (Pfizer-BioNTech) COVID-19 Vaccine in Healthcare Workers: The Effect of Age and Vitamin D

Background: Controlling the spread of the COVID-19 pandemic relies heavily on worldwide immunization programs. Most of the current approved vaccines utilise a two-dose strategy to prime-boost the immune system. To enable larger groups of patients to receive the first dose, the UK government increased the gap between the two doses from three to 12 weeks. Here we report on the immunogenicity of the first dose.Methods: Anti SARS-CoV-2 IgG production (quantitative Abbott immunoassays) and vitamin D (25-hydroxyvitamin D (25(OH)D; LCMS) and 1-α,25-dihydroxyvitamin D (1,25(OH) 2 D, LCMS)) were measured in a group of 105 HCW, post immunization with the Pfizer/BioNTech vaccine.Findings: The anti-Spike IgG Ab response showed minimal change within the first week, rapidly peaked 3·2 weeks post immunization, subsequently decreasing to the nadir at 8 weeks prior to the scheduled second dose being administered. All subjects who responded with positive anti-Spike IgG Abs, retained significant levels at 8 weeks. Response to immunization was significantly modified by age and replete vitamin D status (25(OH)D>50 nmol/L).Interpretation: The results indicate that in this cohort 1) Ab levels are greatest 3-4 weeks post the first dose of the Pfizer/BioNTech vaccine 2) Abs are still circulating eight weeks post first dose 3) age significantly modifies the initial Ab response, the youngest decile having a greater peak and faster decline, resulting in 4) no significant difference in Ab concentration with age at W8 and 5) baseline vitamin D affected the peak of response, with vitamin D replete individuals showing the strongest Ab response.Funding Information: Abbott Diagnostics Ltd supplied the kits used to quantify the anti-SARS -CoV-2 Spike IgG and technical support as well as provided financial support for sample collections.Declaration of Interests: Abbott Diagnostics Ltd provided the necessary immunoassay for analysis of the samples for SARS-CoV-2 IgG and financial support for collection of samples. SR and MB work at Abbott Diagnostics Ltd. All other authors have no conflict of interest. Ethics Approval Statement: All participants provided written informed consent. The study was approved by the Health Research Authority Health and Care Research Wales ethical committee (IRAS#292799).