The phase I study will be conducted on a pool of participants in the U.S. who will be offered the opportunity to receive a 30-µg booster of the current vaccine six to 12 months after receiving their initial two-dose regimen. The study will evaluate up to 144 phase I participants in two age cohorts, 18-55 and 65-85 years of age. Participants will be assessed at the time they receive the third dose, then one week and one month after.

The companies are also in discussions with global regulatory authorities, including the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA), regarding the clinical study of a variant-specific vaccine with a modified messenger RNA sequence. This new construct would be based on the B.1.351 lineage that was first identified in South Africa. This is in alignment with the FDA's updated guidance regarding emergency use of COVID-19 vaccines to address SARS-CoV-2 variants.