Objective The current study aimed to compare the differences in clinical characteristics and prognosis of elderly patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection between patients who were vaccinated and those not and to explore the clinical significance of vaccination for the elderly.Methods A total of 92 elderly patients (≥60 years old) with SARS-CoV-2 infection who were admitted to Chengdu Public Health Clinical Center from December 10, 2020, to May 2, 2022, were included, and they were grouped according to whether vaccinated. The differences in clinical manifestations, laboratory examinations, imaging, treatment, prognosis, hospitalization time, and nucleic acid conversion time between the two groups were compared in this study. Results A total of 92 elderly patients were included, with a male-to-female ratio of 1.3:1, and a median age of 66 (62, 71) years old. There were 79 patients in the vaccinated group and 13 in the unvaccinated group. The positive rate of total SARS-CoV-2 antibody in 92 patients was 91.3%, and those of IgG and IgM of SARS-CoV-2 antibody were 89.1% and 37%, respectively. The positive rates of total SARS-CoV-2 antibody and IgG of SARS-CoV-2 antibody in the vaccinated group were higher than those in the unvaccinated group (97.5% vs. 53.8%, 96.2% vs. 46.2%) (P<0.01), and COI values of total antibody, IgM and IgG were higher than those of unvaccinated group (P<0.01). The proportions of the initial symptoms of sputum, ground-glass opacity or patchy opacity involving both lungs in chest CT in the unvaccinated group were higher than those in the vaccinated group (P<0.05). The white blood cell counts and platelet counts in the vaccinated group were higher than those in the unvaccinated group, whereas the prothrombin time and D-dimer were lower than those in the unvaccinated group (P<0.05). COI values of total antibody in the 3-doses group were higher than those in the 2-doses group, and the white blood cell counts in the 3-doses group were higher than those in the 2-doses group (all P<0.05). During hospitalization, asymptomatic infection (58.2%) and general type (53.8%) was the most common in the vaccinated and unvaccinated group, respectively. Patients in the unvaccinated group were more likely to progress to severe status than the vaccinated group during hospitalization (15.4% vs. 0%, P=0.019). The unvaccinated group received more treatments of intravenous immune globulin, non-invasive and invasive mechanical ventilation, plasma after immunization of vaccine and convalescent plasma of SARS-CoV-2 infected patients than those of the vaccinated group (P<0.05). Patients in the unvaccinated group developed a higher proportion of respiratory failure, secondary infection, acute respiratory distress syndrome, and heart failure than in the vaccinated group (P< 0.05). The median lengths of hospitalization and nucleic acid conversion in the unvaccinated group were 22 (7, 32) days and 13 (2, 20) days, which were longer than those in the vaccinated group [8 (7, 12) days, 2 (2, 7) days] (all P<0.05). Conclusions Vaccination of SARS-CoV-2 can improve the positive rate of total SARS-CoV-2 antibody and IgG of SARS-CoV-2 antibody in elderly patients with SARS-CoV-2 infection, milder disease status, and can shorten the time of hospitalization and nucleic acid conversion. These results suggest that the COVID-19 vaccine can reduce the disease and improve the prognosis in the elderly.