Safety and Immunogenicity of an Intranasal RSV Vaccine Expressing SARS-CoV-2 Spike Protein (COVID-19 Vaccine) in Adults

Inclusion Criteria: * Healthy adults ≥18 and \<56 years (Cohort A) and ≥56 years and \<70 years (Cohort B) as determined at the day of signing informed consent * SARS-CoV-2 RT-PCR (nasal swab) negative at Day 1 pre-dose * Women of childbearing potential (WOCBP) or male subjects with partners who are WOCBP must agree to practice contraception during their study participation from the signing of informed consent for at least 3 months after the final MV-014-212 administration. * Written informed consent Exclusion Criteria: * Diagnosis of chronic pulmonary disease (e.g. chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, cystic fibrosis). Resolved childhood asthma is not exclusionary. * Immunocompromised state due to comorbidities or other conditions as detailed in the study protocol * Nasal obstruction (including due to anatomic/structural causes, acute or chronic rhinosinusitis, or other causes) * Receipt of any other SARS-CoV-2, other experimental coronavirus, or experimental RSV vaccine at any time prior to the study * Healthcare worker, long-term care or nursing home facility resident or employee, member of an emergency response team, or other occupation with high risk of exposure to SARS-CoV-2, and those working outside the home in customer facing occupations (e.g. waiter, cashier or store clerk, public transportation or taxi driver) * Positive serum pregnancy test during Screening and/or positive urine pregnancy test on Day 1 * Breastfeeding during any period of study participation * Occupational or household exposure to children \<5 years of age or to immunocompromised persons * Receipt of or scheduled to receive any other SARS-CoV-2 vaccine prior to Day 1. Once dosed with MV-014-212, subjects should not receive an authorized or approved COVID-19 vaccine until after the Day 57 visit (single-dose subjects) or the Day 92 visit (two-dose subjects) * Any medical disease or condition that, in the opinion of the PI, precludes study participation. This includes acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial