A deep dive into the immunological and hematological responses to COVID-19 vaccines; implications for clinical practice

Introduction: The COVID-19 pandemic has shown the importance of vaccines in controlling the spread and severity of diseases. The immune responses elicited by different vaccines are important for the assessment of their effectiveness and safety. This study compares immunological and hematological responses to Pfizer, AstraZeneca, and Sinopharm vaccines with unvaccinated subjects to identify patterns and predictors of vaccine-induced immunity. Objectives: This study aimed; 1) to assess the immune and hematological responses induced by Pfizer, AstraZeneca, and Sinopharm vaccines, 2) to compare cytokine levels, IgG production, and leukocyte profiles among vaccine recipients and unvaccinated individuals and 3) to determine the predictors of immune marker activation and finally to characterize response categories through statistical analyses. Patients and Methods: This comparative study analyzed demographic data, leukocyte counts, cytokine levels, and IgG levels from a population vaccinated with Pfizer, AstraZeneca, or Sinopharm vaccines and also included unvaccinated controls. Moreover, multivariate and latent class analysis were conducted to bring out any important predictors and trends of the response. The time comparison until IgG peak levels by groups was established by conducting a survival analysis. Results: Pfizer vaccine recipients had the highest IgG levels (10,489 ± 1167 U/mL) and elevated cytokine levels, including IL-2 (76.73±14.64 pg/mL) and TNF-α (61.96 ± 1.71 pg/mL). AstraZeneca recipients showed increased eosinophil and basophil counts, suggesting mild inflammatory responses. Vaccination was a strong predictor of immune activation (P < 0.001), with distinct responder groups identified through latent class analysis, dominated by Pfizer recipients. Survival analysis showed earlier IgG peak times in vaccinated than in unvaccinated. Conclusion: This is a landmark study defining the differential immunogenicity and safety profiles of Pfizer, AstraZeneca, and Sinopharm vaccines. Pfizer showed the strongest immune activation, while AstraZeneca revealed mild subclinical inflammation. These results provide key insights into vaccine-induced immunity, which support their safe and effective administration in fighting against COVID-19.