Risk of extended viral shedding of Omicron BA.2 in Shanghai: Implications for vaccination strategy optimization

In late March 2022, an outbreak of coronavirus disease 2019 (COVID-19) caused by the Omicron BA.2 strain occurred in Shanghai, China. This retrospective study aimed to investigate the clinical characteristics, laboratory parameters, and vaccine protectiveness related to this disease in China.

We conducted a single-center retrospective study on 735 patients with COVID-19 hospitalized from March 17 to May 14, 2022. Clinical characteristics were analyzed based on vaccination status and viral shedding time (VST). The least absolute shrinkage and selection operator (LASSO) regression and 5-fold cross-validation were applied to screen factors linked to the rate of the VST. Generalized linear models were further applied to estimate the odds ratios for factors influencing the VST.

The median VST of unvaccinated patients was 13 (11-16) days, which was longer than that of patients vaccinated with one or two doses (11 [9-13] days) and with completed booster doses (11 [8-12] days). A LASSO regression model and 5-fold cross-validation showed that age of ≥60 years (β = 0.01), pneumonia (β = 0.53), and higher number of comorbidities (β = 0.69) were positively associated with the VST, whereas the platelet count (β = -8.0×10^-5) was inversely associated with the VST. Subgroup analysis revealed that the number of vaccinations was significantly associated with a decreased VST among patients with renal dysfunction (odds ratio [OR], 0.65; 95% confidence interval [CI], 0.44-0.97; P = 0.034) and patients with two or more comorbidities (OR, 0.09; 95% CI, 0.03-0.28; P < 0.001). The lymphocyte count was significantly associated with a decreased VST among patients aged <60 years (OR, 0.51; 95% CI, 0.30-0.85; P = 0.011), patients with normal renal function (OR, 0.41; 95% CI, 0.21-0.80; P = 0.009), and patients with fewer than two comorbidities (OR, 0.49; 95% CI, 0.30-0.80; P = 0.005).

Our preliminary results suggest that the complete and booster vaccination contributes to the viral clearance of Omicron BA.2 variants, while the protectiveness of vaccination is most imperative in patients with impaired renal function and more comorbidities.