RÉSUMÉ
@#Abstract: Objective To investigate the impacts of vaccination with inactivated SARS-COV-2 vaccine on the clinical manifestations and serological responses of COVID-19 patients infected by Delta and Alpha variants. Methods Clinical and experimental data of 341 confirmed SARS-COV-2 patients were collected from The Eighth Affiliated Hospital of Guangzhou Medical University May 1- September 30, 2021. The subjects were divided into Delta and Alpha variant group according to virus variants, and were divided into vaccinated group and unvaccinated group according to whether they had received inactivated COVID-19 vaccine or not. The clinical manifestations and serological responses of patients with Delta and Alpha variant, and vaccinated and unvaccinated patients with Delta and Alpha variants were compared. Results Totally 253 patients were infected with Delta variant (103 vaccinated and 150 unvaccinated patients), and 88 patients were infected with Alpha variant (21 vaccinated and 67 unvaccinated patients). The proportion of asymptomatic infection in Delta variants group was significantly lower than that in Alpha variants group (P<0.01). Delta variant group of vaccination rates and vaccine breakthrough infection rate was 40.7% (103/253) and 22.9% (58/253), were higher than Alpha variant group was 23.9% (21/88) and 8.0% (7/88), difference was statistically significant (χ2= 8.009, 9.484, P<0.01). The proportion of cough and fever in Delta variant group was higher than that in Alpha variant group (both P<0.01), the peak viral load was higher than that of Alpha variant group (P<0.01), the virus duration was longer than that of Alpha variant group (P<0.01), the levels of SAA, CRP and IFN were higher than those of Alpha variant group (all P<0.05), CD4+T cell count was lower than that of Alpha variant group (P<0.05), IgG and IgM levels were lower than those of Alpha variant group (both P<0.01). The proportion of moderate COVID-19 in the vaccinated group was lower than that in the unvaccinated group (P<0.01). In these two variants, the peak viral load of vaccinated group was lower than that of the unvaccinated group (both P<0.01), the duration of virus was shorter than that of unvaccinated group (both P<0.01). The levels of SAA, CRP and IL-6 in the vaccinated group were lower than those in the unvaccinated group (all P<0.05), CD4+T cell level was higher than that of unvaccinated group (both P<0.05), IgG and IgM level were higher than those in unvaccinated group (both P<0.05). Conclusions Delta variant can lead to higher viral load and more severe disease course, which is associated with vaccine breakthrough infection. Inactivated vaccines for COVID-19 can reduce severe illness and death by reducing viral load, disease duration and inflammatory response through humoral and cellular immune mechanisms.