A Phase 1 Study to Assess the Safety and Immunogenicity of JCXH-221, an MRNA-based Broadly Protective COVID-19 Vaccine

Main Inclusion Criteria * Sex: Male or female; female subjects may be of childbearing potential, of nonchildbearing potential, or postmenopausal. * Age: 18 years of age or older, at screening. * Status: Healthy subjects. * Subjects must have completed the full doses for primary vaccination with an approved SARS-CoV-2 vaccine and may have received booster dose(s), with the last vaccination (can be 2nd dose of primary vaccination or booster dose) having occurred at least 4 months prior to enrollment. Main Exclusion Criteria * Current or prior symptomatic or asymptomatic SARS-CoV-2 infection confirmed by an approved or authorized rapid antigen test on Day 1 or within 4 months prior to Day 1. * Subjects with significant exposure (as defined by current CDC guidance) to someone with laboratory confirmed SARS-CoV-2 infection or COVID-19 with the past 14 days prior to the Screening visit. * Subjects with fever or signs of acute infection at the time of enrollment and vaccination. * Subjects who are taking medications that may prevent or treat COVID-19. * Subjects who received convalescent serum or prior therapeutic antibodies against SARS-CoV-2 within 4 months before Day 1. * Subjects with history of myocarditis or pericarditis, or with AEs after mRNA vaccination that are in nature and severity beyond the common AEs expected and necessitating medical intervention. * Subjects with active or suspected immunosuppression, immunodeficiency, or autoimmune disease.