The effects of vaccination on the disease severity and factors for viral clearance and hospitalization in Omicron-infected patients: A retrospective observational cohort study from recent regional outbreaks in China

Abstract

Object: This study attempted to explore the effects of vaccination on disease severity and the factors for viral clearance and hospitalization in omicron-infected patients.

Methods: The clinical manifestations of 3,265 Omicron-infected patients (BA.2 lineage variant; the Omicron group) were compared with those of 226 Delta-infected patients (the Delta group). A Multi-class logistic regression model was employed to analyze the impacts of vaccination doses and intervals on disease severity; a logistic regression model to evaluate the risk factors for hospitalization; R 4.1.2 data analysis to investigate the factors for time for nucleic acid negativization (NAN).

Results: Compared with the Delta group, the Omicron group reported a fast transmission, mild symptoms, and lower severity incidence, and a significant inverse correlation of vaccination dose with clinical severity (OR: 0.803, 95%CI: 0.742-0.868, p<0.001). Of the 7 or 5 categories of vaccination status, the risk of severity significantly decreased only at ≥21 days after three doses (OR: 0.618, 95% CI: 0.475-0.803, p<0.001; OR: 0.627, 95% CI: 0.482-0.815, p<0.001, respectively). The Omicron group also reported underlying illness as an independent factor for hospitalization, sore throat as a protective factor, and much shorter time for NAN [15 (12,19) vs. 16 (12,22), p<0.05]. NAN was associated positively with age, female gender, fever, cough, and disease severity, but negatively with vaccination doses.

Conclusion: Booster vaccination should be advocated for COVID-19 pandemic-related control and prevention policies and adequate precautions should be taken for patients with underlying conditions.

Keywords: COVID-19; hospitalization; public health policy; vaccination; viral clearance.

Figure 1

The effects of different vaccination doses and intervals on disease severity in Omicron infection (A) 7 different vaccination doses and intervals, (B) 5 different vaccination doses and intervals. OR: odds ratio. Error bars represent 95% CI. Unvaccinated individuals infected with Omicron served as the reference category. A multivariate ordered logistic regression model was used to analyze the effects of vaccination doses and intervals on disease severity of the patients. Doses of vaccines were treated as independent variable and three clinical symptom categories, “asymptomatic”, “mild” and “moderate”, were treated as dependent variables and designated to indicate the increasing disease severity, with 3 severe and critical patients excluded from analyses. The analyses showed that regardless of the 7 (A) or 5 categories (B) of vaccination status, the disease severity was significantly reduced only at ≥ 21 days after 3 doses (OR: 0.618; 95% CI: 0.475-0.803, p < 0.001; OR: 0.627, 95% CI: 0.482-0.815, p < 0.001 respectively), with no significant difference found for the other categories.