This study is a multisite ,grouped test-negative case-control , phase Ⅳ clinical trial of an inactivated SARS-CoV-2 vaccine (CoronaVac) manufactured by Sinovac Research and Development Co., Ltd.The purpose of this study is to estimate the protective effectiveness of complete vaccination (measured ≥14 days after the second dose) of CoronaVac against symptomatic SARS-COV-2 infections ,COVID-19 hospitalizations and severe cases.

This study is a multisite,grouped test-negative case-control , phase Ⅳ clinical trial in population aged 18 years and older. The experimental vaccine will be manufactured by Sinovac Research and Development Co.,Ltd.The study is planned to be carried out in ten (10) selected hospitals and their catchment communities in five provinces of the Dominican Republic (DR): National District, La Altagracia, Puerto Plata, Santiago, and Santo Domingo from July 1, 2021 to April 30, 2022 . A total of 1400 subjects will be enrolled with 700 estimated clinic cases who are diagnosed as SARS-CoV-2 infection by real-time polymerase chain reaction (RT-PCR); and 700 estimated clinic controls who have a negative RT-PCR test.And subjects will receive two doses of vaccine for primary immunization .

Inclusion Criteria:

• Aged ≥18 years;
• Permanent residents of study provinces;
• Able and willing to provide informed consent to participate in the study;
• Able and willing to provide nasopharyngeal swab and venous blood sample;
• Able and willing to complete a questionnaire survey for collecting information on histories of COVID-19 vaccination and disease;
• Considered as suspected cases of SARS-CoV-2 infections by the physicians in the study clinics according to DR national protocol.

Exclusion Criteria:

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The participants will be recruited from clinic patients in 10 study hospitals in five provinces. Patients who visit the emergency room (ER), fever or respiratory disease clinics to seek diagnosis or health care for severe acute respiratory infection symptoms or signs and are considered as suspected cases of SARS-CoV-2 based in DR national COVID-19 clinical guideline will be invited to participate in the study, and 1400 clinic participants will be enrolled, 140 from each hospital.