Safety and Immunogenicity Study of a SARS-CoV-2 (COVID-19) Variant Vaccine (mRNA-1273.351) in Naïve and Previously Vaccinated Adults

This is a phase 1, open-label, randomized clinical trial in males and non-pregnant females, 18 years of age and older, who are in good health, have no known history of COVID-19 or SARS-CoV-2 infection, and meet all other eligibility criteria. This clinical trial is designed to assess the safety, reactogenicity and immunogenicity of mRNA-1273.351 manufactured by ModernaTX, Inc, given in vaccination schedules alone, sequentially, or coadministered with mRNA-1273. mRNA-1273.351 is a novel lipid nanoparticle (LNP)-encapsulated mRNA-based vaccine that encodes for a full-length, prefusion stabilized S protein of the SARS-CoV-2 B.1.351 variant. Enrollment will occur at approximately five domestic clinical research sites. This study includes two cohorts. Cohort 1 will provide rapid information about the immunogenicity of mRNA-1273.351 in a previously vaccinated group. This cohort can inform near term public health decisions if the variant virus becomes more widespread. Cohort 2 will evaluate different strategies for generation of cross protective immune responses in a naïve population. This cohort will take longer to provide information on the immunogenicity of mRNA-1273.351, but is important to inform future public health strategies. Cohort 1 will include approximately 60 subjects 18 years of age and older who received two vaccinations of mRNA-1273 at dosages of 50 mcg, 100 mcg, or 250 mcg in the Phase 1 clinical trial (DMID 20-0003). Subjects in Cohort 1 will receive a single intramuscular (IM) injection of the designated vaccine and will be followed through 12 months after vaccination. Follow-up visits will occur on Days 8, 15, and 29, as well as 3, 6, and 12 months after the vaccination. Cohort 2 will include approximately 150 participants 18 through 55 years of age who have not received a COVID-19 vaccine, have no known history of COVID-19 or SARS-CoV-2 infection, and do not have underlying conditions that are associated with an increased risk of severe illness from SARS-CoV-2 infection. Enrollment may close before the full 150 participants based on estimates on the timing of immunogenicity results and the need to inform public health decisions. They will be randomly assigned to one of 8 treatment arms and will receive 2 or 3 IM injections of the vaccine and followed through 12 months after the last vaccination. Follow-up visits will occur 7, 14, and 28 days after each vaccination, as well as 3, 6 and 12 months post the last vaccination. The primary objective is to evaluate the safety and reactogenicity of mRNA-1273 and mRNA-1273.351 vaccines, in naïve and previously vaccinated individuals. The secondary objective is to assess humoral immunogenicity of mRNA-1273 and mRNA-1273.351 vaccines, in naïve and previously vaccinated individuals.