The impact of vaccination on patients with COVID-19 during the wave of Omicron in Shanghai

BACKGROUND: The global health has been affected by the COVID-19 pandemic persistently, of which Omicron is currently the predominant variant. However, the impact of vaccination on Omicron remained uncertain. OBJECTIVE: This study sought to explore the effect of vaccination on patients infected with Omicron. METHODS: A retrospective observational cohort was conducted in the largest Fangcang shelter hospital in Shanghai from April 1 to May 30, 2022. The demographics, length of hospital stay, clinical symptoms, the comorbidities and vaccination status were recorded. Clinical outcomes of the vaccinated and non-vaccinated groups were compared and analyzed. RESULTS: Of the 3,119 patients who fulfilled the eligibility criteria and were enrolled in the study, 2,226 (71.4%) patients had received nCoV-19 vaccine while 893 (28.6%) patients had not received it before admission. Patients in the vaccinated group had significantly shorter length of hospital stay than those in the unvaccinated group (15.48 ± 2.708 vs. 15.85 ± 3.102, p < 0.001). More asymptomatic patients were observed in the vaccinated group than the non-vaccinated (70.4 vs. 64.5%, p < 0.001). Further subgroup analysis demonstrated that the older the age, the more significant the difference was (p < 0.005). CONCLUSIONS: Vaccination was associated with a significant reduction in the severity of Omicron infection compared with no vaccination. Vaccination appears to make Omicron-infected people with milder symptoms than unvaccinated people. This suggests the potential effectiveness of current vaccines against Omicron.