Objective: The cytokine interleukin-15 is widely known for helping natural killer cells and CD8 T cells development and maintain homeostasis, but recent research reveals that IL-15 also mediates the antiviral responses of both cell types during an active immune response. Aim of the study: study Interleukin-15 gene expression in vaccinated individuals (Pfizer Sinopharm and AstraZeneca vaccines) and critical cases infected with COVID-19 in Iraqi individuals, for the purpose of investigating the role of IL -15 gene in determining the immune response in vaccinated individuals (Pfizer – AstraZeneca- Sinopharm vaccines) and  COVID-19 patients. Study design: This study was conducted between the period from January and March 2022. A total number of 179 (male and female) blood samples were collected from Ibn AI-Khatib Hospital and health centers (AL-Sindibad health center, AL Rasheed health center and other places). Immunological assay for evaluation of anti-COVID-19 IgG and IgM was accomplished by ELISA technique. Molecular analysis was achieved by real time PCR to confirm our results by detecting of IL-15 genelevels. Results: Showed that the Sinopharm, BioNTech and AstraZeneca vaccines groups exhibited the highest neutralization potential compared to the unvaccinated controls. The results indicated that Sinopharm vaccines generally induced the highest amounts of SARS-CoV-2 reactive IgM and IgG compared to other vaccines (7.31 ± 1.52) IgM and (38.84 ± 26.35) IgG P -value (0.001). The critical patient showed a highly significant difference between males and females of IgM P- value (0.002). The patients had the highest IgM production in males. The Sinopharm vaccine had the highest productivity of IgG in the two groups compared to Pfizer and AstraZeneca vaccine. The critical patient, Sinopharm vaccine and AstraZeneca vaccine showed significant difference between (41-70) (21-40) groups of IgM. The critical patient showed a highly significant difference between males and females of IgG P- value (0.006). The patients had the highest IgG production in males. The critical patient and Pfizer vaccine showed significant difference between (41-70) (21-40) groups of IgG. The IL-15 geneshowed no effect with COVID-19. Conclusion: The study showed that Pfizer, Sinopharm and AstraZeneca vaccines produced IgM and IgG against COVID-19 in terms of age and gender compared to the unvaccinated individuals, with no effect of the booster dose compared to the second dose.