The goal of this observational study is to explore the influence of Covid-19 infection and risk factors of severe outcomes in vulnerable population including patients with chronic liver disease, malignant tumor, autoimmune disease, medical staff.

The main questions it aims to answer are:

1. The clinical characteristics of vulnerable population after Covid-19 infection.
2. Risk factors for severe illness in vulnerable groups after infection with the Covid-19.
3. The impact of Covid-19 infection on the progression of underlying diseases.

Information of participants will be collected such as gender, age, underlying diseases, medication status, vaccination status, clinical and biochemical indicators.

Researchers will compare the mild and severe outcomes after Covid-19 infection to identify the "truly vulnerable" population and explore the potential mechanism and intervention for these population.

Inclusion Criteria:

1. Sign the informed consent form before enrollment, and be able to complete the research according to the requirements of the research protocol.
2. Enrolled patients need to have basic diseases, including chronic liver disease, chronic kidney disease, chronic lung disease, solid tumors, AIDS, rheumatic immune diseases, diabetes, etc.
3. When entering the group, patients with new crowns need to be confirmed by evidence of a positive test for new coronavirus nucleic acid (CT value <35) or a positive test for new coronavirus antigen.

Exclusion Criteria:

1. Participate in clinical trials of other investigational drugs or medical devices within 3 months before screening, and take experimental drugs or use medical devices.
2. Positive pregnancy test during lactation or screening period.
3. Subjects who, in the investigator's opinion, have other factors that are not suitable for participating in this study.

The target population was population with underling disease from single-centre and medical staff from multiple centers in Chongqing.