Evaluation of COVID-19 Immune Barrier and Reinfection Risk

Study Overview
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Brief Summary
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The goal of this observational study is to evaluate the protective effect of immune barrier on secondary infection after COVID-19 (coronavirus disease 2019) vaccination or COVID-19 virus Omicron B A. 5.2 strain infection by dynamically monitoring the COVID-19 antibody titer, cellular immune function and the occurrence of secondary infection of healthy participants, mainly medical staff in our hospital, to understand the cross protective effect of COVID-19 antibody on different variants of Omicron, and explore the best time to use COVID-19 vaccine to strengthen immunity after Omicron mutant infection.

Detailed Description
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This study is a single center, prospective, non-intervention study. It is planned to recruit 300 medical and nursing participants, administrative and logistics participants or other participants who can cooperate with the follow-up for 48 weeks to voluntarily join the group. Participants will be investigated about the vaccination history of COVID-19 vaccine, whether they have ever been infected with COVID-19, the time of initial infection with COVID-19, and following clinical symptoms.The COVID-19 antibody titer of peripheral blood will be used for baseline. The participants will be divided into positive group and negative group according to the COVID-19 antibody titer results,then they wii be followed up for 48 weeks.If the participants have no symptoms related to COVID-19 infection, COVID-19 antibody and COVID-19 nucleic acid will be tested every 4-8 weeks according to the epidemic situation (the specific visit time is initially set as 0 week, 6 ± 2 weeks, 12 ± 4 weeks, 20 ± 4 weeks, 28 ± 4 weeks, 36 ± 4 weeks, 48 ± 4 weeks). There will be about 7 visits in total, according to the epidemic situation and the time of secondary infection of the participants). If the nucleic acid turns to be positive, we will consider it as the asymptomatic infection, then we will collect nasal/pharyngeal swabs for gene sequencing of virus strains, and terminate the study. If the participants get fever, fatigue, sore throat, cough, nasal congestion, runny nose, muscle soreness or headache and other symptoms related to COVID-19 infection during the study period, they need to test the COVID-19 antigen or COVID-19 nucleic acid within 48 hours. If it is positive, we will collect nasal/pharyngeal swabs for gene sequencing of virus strains, and terminate the study in advance.

Official Title
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Evaluation of COVID-19 Immune Barrier and Reinfection Risk

Conditions
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COVID-19 Infection, Immunization; Infection

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: No age limit, no gender limit; Medical staff, administrative and logistics staff who work in the Third Affiliated Hospital of Sun Yat-Sen University or other participants who can cooperate with the follow-up for 48 weeks; The participants need to be sure whether they have ever been infected with COVID-19, and need to be clearly remember the time when they first infected with COVID-19. Exclusion Criteria: Have the following serious respiratory diseases: such as asthma, bronchiectasis, chronic obstructive pulmonary disease, pulmonary interstitial disease, tuberculosis and other respiratory diseases that may interfere with symptom observation; Those with other serious diseases or disease history that affect immune function, including but not limited to uncontrolled and unresectable malignant tumors,hematological diseases, cachexia, active bleeding, severe malnutrition, mental diseases, autoimmune diseases, HIV, etc. Those who have long-term assignment plans and cannot return to the hospital regularly for follow-up.
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| COVID-19 Antibody Group 1<br>Participants will be divided into positive group and negative group according to the baseline of COVID-19 antibody titer.Group 1 is for those COVID-19 antibody are positive. | |
| COVID-19 Antibody Group 2<br>Participants will be divided into positive group and negative group according to the baseline of COVID-19 antibody titer.Group 1 is for those COVID-19 antibody are negative. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The incidence of COVID-19 reinfection in COVID-19 antibody positive and negative groups. | This study is an observational study. The incidence of COVID-19 reinfection is mainly based on the participants with positive COVID-19 nucleic acid test. The proportion of participants with positive COVID-19 nucleic acid test in the total number during the observation period after 48 weeks observation will be counted. | 48weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Dynamic changes of COVID-19 antibody titer in 48 weeks after COVID-19 infection. | We will test COVID-19 antibody every 4-8 weeks and record the data to observe the dynamic change of titer. | 48weeks | 
| Dynamic changes of cellular immune function in 48 weeks after COVID-19 infection. | Flow cytometry will be used to detect the cellular immune function of participants every 4-8 weeks, and record data to analyze its dynamic changes. | 48weeks | 
| Antibody titer of COVID-19 in uninfected persons. | The uninfected person refers to the participant who is still uninfected with COVID-19 at the end of our study. We will record and analyze the dynamic change of COVID-19 antibody titer within 48 weeks. | 48weeks | 
| The cellular immune function of COVID-19 in uninfected persons. | We will record and analyze the dynamic change of the cellular immune function by flow-cytometry within 48 weeks. | 48weeks | 
| The change of antibody titer in uninfected people after COVID-19 vaccine. | We will test and analyze the changes of COVID-19 antibody titer of uninfected people within 48 weeks after the booster immunization with COVID-19 vaccine. | 48weeks |