Study to Evaluate the Efficacy of IN STI-9199 in Treating Symptomatic COVID-19 in Outpatient Adults and Adolescents

Inclusion Criteria: * Otherwise healthy, positive for COVID-19 by an EUA-approved rapid antigen or PCR test, has ongoing "mild to moderate illness or symptoms" with symptom onset starting \< 5 days prior to screening visits * Must provide written informed consent/assent if a minor which includes signing the institutional review board/independent ethics committee approved consent form prior to participating in any study related activity * Willing and able to comply with study procedures and follow-up visits * Willing to follow all contraception guidelines Exclusion Criteria: * In the Investigator's opinion, has progressive symptoms with likely imminent (24-48 hours) hospitalization or severe COVID-19 illness/symptoms * Any medical condition that, in the Investigator's or designee's opinion, could adversely impact participant safety or key objectives of the study * Has a prior history of long COVID * Has a clinically documents acute infection other than COVID-19 * Known or suspected pregnancy, planned pregnancy, a positive pregnancy test at screening or are breastfeeding * Has participated, or is participating in a clinical reserach study evaluating COVID-19 convalescent plasma, mAbs against SARS-CoV-2, or IV immunoglobulin within 2 months or less than 5 half-lives of the investigational product (whichever is longer) prior to the screening visit