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.

Exclusion Criteria:

1. Subject with a history of SARS-CoV-2 vaccinations within 1 months before
randomization.

2. Subject with a history of SARS-CoV-2 infection within 6 months before randomization.

3. With any serious infection requiring systemic anti-infective therapy within 14 days
before randomization.

4. Allergic to the investigational agent or any components of the formulation. Pregnant
or breast-feeding women.

5. Women of childbearing potential who are unwilling to practice highly effective
contraception during the study, and for at least 6 months after the study; Sexually
active men who are unwilling to use medically acceptable birth control during the
study period.

6. Have other conditions not suitable for inclusion as judged by the investigator.