inclusion criteria: 1、18-65 years old at the signing of informed consent. 2、household contacts of individual with symptomatic covid-19. symptomatic covid-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or rt-pcr) positive for sars-cov-2 and must fulfill the following criteria 1) collection of the first positive sars-cov-2 test sample less than 24 hours before randomization, 2) have at least one symptom attributable to covid-19. 3、rt-pcr test negative (with nasopharyngeal \[np\] swab samples) or rapid antigen test negative at the time of screening and without any suspicious covid-19 symptoms within 2 weeks before randomization. 4、subject expects to be living in the same household with the symptomatic covid-19 cases during the whole study period.

inclusion criteria: 1、18-65 years old at the signing of informed consent. 2、household contacts of individual with symptomatic covid-19. symptomatic covid-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or rt-pcr) positive for sars-cov-2 and must fulfill the following criteria 1) collection of the first positive sars-cov-2 test sample less than 24 hours before randomization, 2) have at least one symptom attributable to covid-19. 3、rt-pcr test negative (with nasopharyngeal \[np\] swab samples) or rapid antigen test negative at the time of screening and without any suspicious covid-19 symptoms within 2 weeks before randomization. 4、subject expects to be living in the same household with the symptomatic covid-19 cases during the whole study period.

inclusion criteria: 1、18-65 years old at the signing of informed consent. 2、household contacts of individual with symptomatic covid-19. symptomatic covid-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or rt-pcr) positive for sars-cov-2 and must fulfill the following criteria 1) collection of the first positive sars-cov-2 test sample less than 24 hours before randomization, 2) have at least one symptom attributable to covid-19. 3、rt-pcr test negative (with nasopharyngeal [np] swab samples) or rapid antigen test negative at the time of screening and without any suspicious covid-19 symptoms within 2 weeks before randomization. 4、subject expects to be living in the same household with the symptomatic covid-19 cases during the whole study period.

inclusion criteria: 1、18-65 years old at the signing of informed consent. 2、household contacts of individual with symptomatic covid-19. symptomatic covid-19 cases (index case) to be identified as those symptomatic and recently tested (rapid antigen test or rt-pcr) positive for sars-cov-2 and must fulfill the following criteria 1) collection of the first positive sars-cov-2 test sample less than 24 hours before randomization, 2) have at least one symptom attributable to covid-19. 3、rt-pcr test negative (with nasopharyngeal [np] swab samples) or rapid antigen test negative at the time of screening and without any suspicious covid-19 symptoms within 2 weeks before randomization. 4、subject expects to be living in the same household with the symptomatic covid-19 cases during the whole study period.