Hematological and inflammatory changes following Pfizer-BNT162b2 mRNA vaccination in young healthy adults

Introduction COVID-19 infection causes significant changes in certain hematological markers and increases inflammatory severity, such as NLR, LMR, PLR, and Ferritin. In contrast, the Pfizer-BNT162b2 mRNA-based vaccine does not induce high levels of inflammation. Methods A prospective cohort study, conducted at the University of Diyala from January 2022 to January 2023, assessed the immune response to the Pfizer-BNT162b2 mRNA vaccine in 45 healthy, unvaccinated medical students aged 18 to 23. The study evaluated Complete Blood Count, proinflammatory cytokines, ferritin, and anti-IgG antibodies at the time of the second dose of vaccination and 4 weeks after the second dose of the vaccine. Biomarkers were analyzed using CBC instrumentation, ELISA, and Cobas e411 assays, with ethical approval granted for the study. Results Hemoglobin levels remained stable, while red blood cell (RBC) volume and RDW-CV significantly decreased. RBC indices (MCH, MCHC, HCT) increased, and total leukocyte counts slightly declined with a notable granulocyte rise. The platelet count remained stable; however, the plateletcrit decreased, while MPV and PDW increased. NLR and PLR levels increased significantly, whereas LMR levels decreased. No significant change occurred in PHR, SIRI, or AIRI. Inflammatory markers (TNF-α, ferritin, CD256/APRIL) and anti-spike IgG levels significantly increased after 1 month. Anti-spike IgG levels showed no strong correlations with SIRI, AIRI, PLR, PHR, or MLR, though significant intercorrelations were found among hematological ratios (e.g., PLR with PHR, SIRI, AIRI; LMR with AIRI). Conclusion Pfizer-BNT162b2 mRNA vaccine had a significant impact on the organized redistribution of immune cells.