Vaccination reduces viral load and accelerates viral clearance in SARS-CoV-2 Delta variant-infected patients

Objective The purpose of this study was to investigate vaccine effectiveness in relieving symptoms in patients with the SARS-CoV-2 delta (B.1.617.2) variant. Methods In this retrospective study, 31 patients did not receive any vaccine (non-vaccination, NV), 21 patients received 1-dose of inactivated vaccine (one-dose vaccination, OV), and 60 patients received at least 2-dose inactivated vaccine (two-dose vaccination, TV). The baseline data, clinical outcomes and vaccination information were collected and analyzed. Results Patients in the OV group were younger than those in the other two groups (p = 0.001), but there was no significant difference in any of the other baseline data among the three groups. The TV group showed higher IgG antibody levels and cycle threshold values of SARS-CoV-2 than the NV and OV groups (p < 0.01), and time to peak viral load was shorter in the TV group (3.5 +/- 2.3 d) than in the NV (4.8 +/- 2.8 d) and OV groups (4.8 +/- 2.9 d, p = 0.03). The patients in the TV group (18%) showed a higher recovery rate without drug therapy (p < 0.001). Viral clearance time and hospital stay were significantly shorter in the TV group than in the NV and OV groups (p < 0.01), and there were no significant differences in these parameters between the OV and NV groups, but IgG values were higher in the OV group (p = 0.025). No severe complications occurred in this study. Conclusions Our results suggest that 2-dose vaccination can reduce viral load and accelerate viral clearance in patients with the delta variant and enhance the protection afforded by IgG antibodies in vivo. Key Messages In this study, our results shows that two-dose vaccination can reduce viral loads and accelerate viral clearance, and two-dose vaccination enhance the protection of IgG antibodies in vivo; however, one-dose vaccination did not confer protective effectiveness.