Severity and Vaccine Effectiveness in Patients With the Omicron Variant of COVID-19 in Suzhou: A Retrospective Single-Center Study.

Background The Omicron variant of the coronavirus disease 2019 (COVID-19) virus has spread rapidly worldwide, even in areas with high vaccination rates. Consequently, it has further exacerbated the current global pandemic. In this study, we aimed to characterize the clinical severity of patients with the COVID-19 variant Omicron and analyze vaccine effectiveness in predicting clinical severity. Methodology A total of 142 patients who contracted the COVID-19 virus in the Omicron era were retrospectively studied, and differences in their clinical severity were analyzed. They were stratified as follows: unvaccinated vs. vaccinated, unvaccinated vs. one to two vaccine doses vs. three vaccine doses, and cycle threshold (CT) values ≤ 28 vs. CT > 28. Results Of the 142 patients, 27 were asymptomatic, 83 had mild disease, and 32 had moderate disease. The median age was 32 years for asymptomatic patients vs. 31 years for those with mild disease vs. 59 years for those with moderate disease (P＜0.05), and the direct medical hospitalization costs were ¥4901 for asymptomatic patients vs. ¥5259 for those with mild disease vs. ¥8378 for those with moderate disease (P＜0.05). Of the 142 patients, 112 (78.8%) were vaccinated, 11 (7.7%) had one vaccine dose, 63 (44.4%) had two vaccine doses, and 38 (26.7%) received three vaccine doses. The median direct medical cost in the vaccinated group was significantly lower than that in the unvaccinated group (¥5470.5 vs. ¥7535.5, P＜0.05). For ORF1ab and N genes, hospital stay length and direct medical cost significantly decreased in the group with CT values > 28 compared with those in the group with CT values ≤ 28 (P＜0.05). Multiple regression analysis showed that being ≥ 60 years old could be a predictor of moderate disease severity in patients, and three vaccine doses could be effective against moderate COVID-19. Conclusion Mild infection is the main clinical manifestation of the Omicron variant. Vaccination can significantly decrease direct Omicron-associated medical costs. Although vaccination cannot provide protection against severe disease caused by this variant, three vaccine doses are highly effective in preventing moderate COVID-19.