A Phase I Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of Single and Multiple Ascending Doses of Inhaled MBS-COV (SNS812) in Healthy Participants

Inclusion Criteria: * Body mass index (BMI) between 18.0 and 32.0 kg/m2 (inclusive). * No serious or chronic underlying disease which would adversely affect the study conduct and data interpretation per the investigator. * Female participants should have negative results in serum pregnancy test at screening and negative urine pregnancy test at admission * Participants with normal spirometry (FEV1: 90% or greater) results at screening or day -1. * Both male and female participants and their partners of childbearing potential must agree to use two medically accepted methods of contraception. * Participants should have normal (or abnormal but not clinically significant) laboratory results per the PI's judgement including the hematology, biochemistry, coagulation indices, and urinalysis. * Participants should have a normal (or abnormal but not clinically significant) 12-lead ECG at screening and day -1 and chest X-ray at screening * Participants should be willing to cooperate and able to participate in this study, comply with all protocol requirements, and sign an informed consent. * Current non-smokers and those who have not smoked within the last 3 months. This includes the use of cigarettes, e-cigarettes, and nicotine replacement products. * Nasopharyngeal or nasal swab sample of Participants collected for COVID-19 antigen rapid test at screening and qRT-PCR test on Day -1 should be negative. Exclusion Criteria: * The participant has a known history of, or a positive test result for, hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV), or human immunodeficiency virus (HIV) at screening. * As reported by the participant has severe cardiovascular disease, neurological disease, hematological disease, infectious disease, mental disorder, liver disease, gastrointestinal disease, lung disease, endocrine disease, immune disease or kidney disease, or has a history of the above diseases, or other symptoms known to interfere with the absorption, distribution, metabolism, or excretion of the medicine, or other conditions that the investigator believes will increase the risk of the participant and might interfere with the study conduct and results interpretation. * The participant has history or presence of active lung disease (i.e., asthma, chronic obstructive pulmonary disease \[COPD\], pulmonary fibrosis, hemoptysis, bronchiectasis) or prior intubation. * The participant has upper respiratory infection within the 3 months prior to the first dose of study drug. * Consumed more than 14 units of alcohol per week in the 6 months before screening (1 unit of alcohol = 360 mL of beer or 45 mL of spirits with 40% alcohol content or 150 mL of wine) or have taken alcohol products in the 48 hours prior to administration, or those who have a positive alcohol breath test result at screening and day -1. * Unwillingness to abstain from the consumption of any caffeine or alcohol-containing food or drinks that may influence the drug metabolism from 48 hours before administration. * History of drug abuse or a positive drug abuse (barbiturates, methamphetamine, benzodiazepines, morphine/opiates, phencyclidine (PCP), amphetamines, tetrahydrocannabinol (THC), methylenedioxymethamphetamine (MDMA), cocaine, methadone, and cotinine) test result at screening and day -1. * Female participants who are lactating. * Use of prescription or non-prescription drugs, including vaccine within 14 days or 5 half-lives (whichever is longer) prior to the first dose of study drug. * The subject has received an experimental agent (vaccine, drug, biologic, device, blood product or medication) within 1 month prior to the first dose of study drug and will receive another experimental agent during the duration of this study. * The participant has a history of frequent nose bleeding. * Participants with known allergic reactions to the study drug or its excipients. * The participant has an acute sinusitis or history of chronic sinusitis, a history of active allergic rhinitis (AR), history of perennial allergic rhinitis (PAR), or current seasonal allergic rhinitis (SAR), or recent viral rhinitis within 2 weeks prior to administration. * The participant has Any nasopharyngeal abnormality that may have interfered with nasal absorption, distribution, or study-related evaluations of signs or symptoms (e.g., polyps, septal deviation). * Blood donation of more than 400 mL within 3 months before screening or more than 200 mL within 4 weeks before screening or plan to donate blood during study period. * Any other clinical condition that, in the Investigator's judgment, would potentially compromise study compliance or the ability to evaluate safety/efficacy.