At present, COVID-19 vaccine is considered as the safest, economic and effective measure to prevent and control COVID-19. Adaptive immunity, including humoral immunity and cellular immunity, plays a role in anti-viral responses. Cellular immunity includes virus specific B cells and T cells, which can provide long-term memory immunity. For acute viral infection, neutralizing antibody is of great significance in preventing infection, while memory cell immunity can maintain a good broad-spectrum and persistence in controlling mutant strains, which is a key factor in controlling viral replication after infection and reducing severe disease and death. However, there is no systematic study on the specific immune response and infection risk of novel coronavirus, and there is no definite conclusion on which specific protective immune response induced by vaccine can reduce the risk of infection. Therefore, this study aims to establish a prospective real-world cohort, analyze the correlation between multiple baseline immune protection indicators and infection risk, follow up the population with breakthrough infection, and monitor the dynamic specific immune response to COVID-19 in peripheral blood and respiratory mucosa. This study will provide an important scientific basis for us to scientifically assess the risk of individual infection with COVID-19.

Inclusion Criteria:

1. Age ≥18 years
2. SARS-CoV-2 nucleic acid testing showed negative within 72 hours

Exclusion Criteria:

1.Do not consent to enroll in this study

Healthcare workers in Nanjing Drum Tower Hospital, Nanjing, China