Effectiveness of COVID-19 Vaccines Against the SARS-COV-2 Delta (B.1.617.2)

Up to now, Corona Virus Disease 2019 (COVID-19) continues to spread rapidly around the world. From the beginning of the epidemic to the present, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has continuously evolved and mutated, producing transmissible and virulent variants. At present, the infection rate of Delta variant strains is still increasing globally. The epidemic strain of novel coronavirus infection in Xi 'an city is δ (B.1.617.2). SARS-CoV-2 Delta has more infectious, higher viral load and shorter incubation period than other SARS-COV-2 delta strains. Several studies have shown that the protective efficacy of vaccines against different SARS-COV-2 virus variants is different, and SARS-COV-2 viral load is closely related to transmission, clinical phenotype and prognosis of infected patients. According to the notice of Xi'an Municipal Health Commission, a total of 2,139 local confirmed cases were reported in Xi 'an on January 10,2022, and the proportion of severe cases was 2.36%, which was significantly lower than the 7% of nation since the second half of 2020. According to the preliminary investigation by the applicant's team, the severe illness rate in Xi'an has decreased significantly, which benefits from the active promotion of domestic vaccination, early intervention, and use of neutralizing antibodies. The purpose of this study is to analyze the effects of vaccination on nucleic acid turning negative, clinical characteristics and prognosis of patients infected with SARS-COV-2 delta, and to clarify the protective effects of vaccination, which is of great significance for the prevention and control of the SARS-COV-2 delta (B.1.617.2) in Xi' an.