Inclusion Criteria:  Is male or non-pregnant female adult ≥ 18 and ≤ 55 years of age Has a body mass index (BMI) < 35 kg/m2. Is healthy as determined by medical history, physical examination, 12-lead electrocardiogram, laboratory assessments, and vital signs at screening. For women of childbearing potential or men, agreement to use at least one highly effective form of non-hormonal contraception or one highly effective form and one effective form of non-hormonal contraception through the course of study treatment and for 3 months after the last dose of IGM-6268. Agrees to the collection of blood, urine, saliva, and nasopharyngeal samples, per protocol.  Exclusion Criteria:  Receipt of any COVID-19 vaccine or contemplating receipt of any COVID-19 vaccine (or participating in a COVID-19 vaccine trial) during this study and follow-up periods (approximately 65 days from enrollment). Subjects are permitted to withdraw at any time if they decide to receive the vaccine History of prior positive SARS-CoV-2 diagnostic test (antigen or NAAT), or positive SARS-CoV-2 serology test, at any time before enrollment. Confirmed or suspected pulmonary or systemic bacterial infection. Current or planned participation in any interventional clinical trial during the study and follow-up periods. History of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. Uncontrolled human immunodeficiency virus (HIV) infection. Nasal polyps (history or physical exam) or any structural abnormality of nose that, in the opinion of the investigator, could compromise administration or receipt of study drug (e.g., nasal septal deviation). History of reactive airway disease or hypersensitivity to any component of study drug or placebo. Use of any nasally-administered drug between 5 days prior to study enrollment and 2 days after receipt of last dose administered.