This is an open-label, prospective observational study in people 18 years of age and older designed to track changes in the dynamics of the respiratory and peripheral blood immune response in people infected with influenza virus and new coronaviruses, and to resolve the characteristics of the virus-induced natural immune response.

The clinical trial enrolls 130 subjects aged 18 years and older with ≥3 months between their last COVID-19/influenza vaccination or respiratory virus infection. Mucosal and peripheral blood samples will be collected from COVID-19-infected and influenza-infected patients during the preinfection, infection, and recovery periods, and cytokines, immune cell typing, immune cell transcription, and specific antibody levels will be examined in these patients. Levels of cytokines, immune cell typing, immune cell gene transcription, specific antibodies, etc.

Inclusion Criteria:

1. volunteers aged 18 years and above at the time of screening;
2. informed consent obtained from volunteers and volunteers/witnesses able to sign the informed consent form;
3. an interval of ≥3 months from the last COVID-19 or influenza vaccination;
4. an interval of ≥ 3 months from the last respiratory viral infection such as COVID-19 or Influenza virus occurs; 5.1 cohort 1：novel coronavirus virus antigen-positive and within 48 hours of onset of symptoms of infection; 5.2 cohort 2：influenza virus antigen-positive and within 48 hours of onset of symptoms of infection; 5.3 cohort 3：novel coronavirus and influenza virus antigen-negative, no febrile symptoms, and no symptoms of viral or bacterial respiratory infections.

Exclusion Criteria:

1. known or suspected concomitant more serious and medically unstable disease in the judgment of the investigator, including: respiratory disease, tuberculosis, acute infections or active chronic disease, hepatic or renal disease, cardiovascular disease (cardiorespiratory failure), hypertension (systolic blood pressure ≥160 mmHg, diastolic blood pressure ≥100 mmHg), malignant tumors, infectious or allergic skin diseases, and the presence of HIV infection;
2. Absence of spleen or functional absence of spleen;
3. immunosuppressive therapy, anti-allergy therapy, cytotoxic therapy, inhaled corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis, and superficial corticosteroid therapy for acute uncomplicated dermatitis) within the past 6 months;
4. Received blood products within the past 3 months;
5. has received other vaccines or investigational drugs within the past 1 month;
6. is receiving anti-tuberculosis treatment;
7. In the judgment of the investigator, due to a variety of medical, psychological, social, or other conditions that are contrary to the trial protocol or that affect the signing of informed consent by the volunteer.

This study is planned to include 50 patients infected with novel coronavirus, 50 patients infected with influenza virus and 30 healthy volunteers.