Study Comparing Safety and Immunogenicity of Intranasal COVID-19 Vaccine and mRNA Booster in Healthy Adults

This is a randomized, comparative, multicenter, open-label, phase I/II trial in France evaluating the safety and immunogenicity of a booster dose of an intranasal COVID-19 vaccine (LVt-001) versus a booster dose of a COVID-19 mRNA vaccine (Pfizer-BioNTech) in healthy adult volunteers. Phase I dose escalating - Primary Objective: To evaluate the safety of three escalating doses of a boost of an intranasal COVID-19 vaccine (LVT-001) expressing SARS-CoV-2 N/S recombinant protein in healthy volunteers. Phase II superiority trial - Primary Objective: To evaluate, using nasal swabs, the superiority of a booster dose of the selected intranasal COVID-19 vaccine (LVT-001) expressing SARS-COV-2 N/S recombinant protein versus a booster dose of the intramuscular COVID-19 mRNA vaccine (Pfizer-BioNTech) in healthy adult volunteers in term of mucosal humoral immune response at Day 28. Trial population: A total of 36 and 202 healthy volunteers will be enrolled in Phase I and Phase II, respectively. Interventions: Phase I: The investigational medicinal product is the intranasal recombinant protein vaccine LVT-001 administered at Day 0 in each nostril: * Cohort A (12 participants): 20 µg * Cohort B (12 participants): 60 µg * Cohort C (12 participants): 120 µg Phase II: Two investigational medicinal products will be compared: * The selected dose of the intranasal recombinant protein vaccine LVT-001, administered at Day 0 in each nostril. * The intramuscular COVID-19 mRNA vaccine (Pfizer-BioNTech), administered as the standard of care booster. Expected Outcomes and Safety Considerations: In Phase I, healthy participants are not expected to benefit directly from the trial aside from the potential theoretical benefit of a mucosal immune response against SARS-CoV-2. Currently, no clinical trial data exist for a nasal protein vaccine in humans. The anticipated risks primarily include local nasal reactions and systemic reactions similar to those observed with other vaccines. Any adverse events following vaccination are expected to be manageable with routine care, as determined by investigators. Given that this is the first human trial of a nasal protein vaccine, the dose-escalation design ensures a safety margin, allowing for careful monitoring before progressing to the next cohort.