HH-120 Nasal Spray for Post-exposure Prevention of SARS-CoV-2

Inclusion Criteria: * 12 to 85 years old. * Participants with potential exposure to index patients (with known positive result of qRT-PCR or rapid antigen test \[RAT\]). * Participants will be randomized no longer than 48 hours from the onset of the COVID-19 related symptom of the index patients. * Participants with a negative RAT result within 2 hours prior to randomization. * Fertile participants must agree to use a highly effective method of contraception. * Participants being able and willing to provide informed consent prior to any study-specific procedure. Exclusion Criteria: * Those with high risk of cardiac events, or severe abnormal functions of liver, kidney, lung, brain and other organs and are deemed as unsuitable to participate in the study (except for those subjects with kidney failure but received regular dialysis, or those with liver dysfunction but stabilized after treatment evaluated by the evaluation of the investigators). * Those comorbid with asthma. * Those with a history of SARS-CoV-2 infection within 3 months prior to randomization. * Those who has received any nasal spray or aerosol inhalation COVID-19 vaccine within 3 months prior to randomization. * Those who experienced symptom of upper respiratory tract infection within 2 weeks prior to randomization, such as nasal congestion, sore throat, shortness of breath (dyspnea), cough, fatigue, fever, headache, etc. * Known history of allergy or reaction to any component of the study drug formulation. * Those who has received other treatment with anti-COVID-19 indication (within 1 month or 5 half-life period prior to randomization, whichever occurs first). * Participants with nasal disease that is inconvenient or intolerant of nasal spray administration. * Other reasons considered by the investigator to be unsuitable for the study.