Coronavirus disease 2019 (COVID-19), an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was responsible for the pandemic decreed on March 11, 2020. Here, we investigated the mRNA expression of interleukin (IL)-1β, IL-8, and IL-1RN in samples collected from patients with and without SARS-CoV-2 infection, who were vaccinated or unvaccinated. This investigation was designed as a qualitative, cross-sectional, comparative, and randomized observational study. Samples were collected through nasal/oral swabs from patients symptomatic for influenza syndrome or SARS. Patients were categorized into three groups: DVAC (patients with SARS-CoV-2 infection and vaccinated), DNVAC (patients with SARS-CoV-2 infection and not vaccinated), and ND (patients without SARS-CoV-2 infection). SARS-CoV-2 was detected through reverse transcription polymerase chain reaction (RT-PCR). Gene expressions of IL-1β, IL-8, and IL-1RN were also evaluated using RT-PCR. Statistically significant differences in IL-8 expression were observed among the study groups (P = 0.033); moreover, clinical signs and symptoms, frequency of hospitalizations, and need for intensive care units showed significant differences. These differences were noted in the DVAC group compared with those in the DNVAC and ND groups. Patients with COVID-19 showed reduced IL-8 expression compared with those with other diseases that also cause influenza syndrome or SARS. These results suggested that the severity of clinical manifestations of patients with COVID-19 reduced after the initial two doses of the CoronaVac/Sinovac vaccine. Moreover, this vaccine reduced mortality and lethality in patients with SARS-CoV-2 infection.