Six-month safety follow-up of an adjuvanted SARS-CoV-2 trimeric S-protein subunit vaccine (SCB-2019) in adults: A phase 2/3, double-blind, randomized study

BACKGROUND: We evaluated the safety of SCB-2019, a protein subunit vaccine candidate containing a recombinant SARS-CoV-2 spike (S) trimer fusion protein, combined with CpG-1018/alum adjuvants. METHODS: This ongoing phase 2/3, double-blind, placebo-controlled, randomized trial is being conducted in Belgium, Brazil, Colombia, the Philippines, and South Africa in participants ≥ 12 years of age. Participants were randomly assigned to receive 2 doses of SCB-2019 or placebo administered intramuscularly 21 days apart. Here, we present the safety results of SCB-2019 over the 6-month period following 2-dose primary vaccination series in all adult participants (≥18 years of age). RESULTS: A total of 30,137 adult participants received at least one dose of study vaccine (n = 15,070) or placebo (n = 15,067) between 24 March 2021 and 01 December 2021. Unsolicited adverse events, medically-attended adverse events, adverse events of special interest, and serious adverse events were reported in similar frequencies in both study arms over the 6-month follow-up period. Vaccine-related SAEs were reported by 4 of 15,070 SCB-2019 recipients (hypersensitivity reactions in two participants, Bell’s palsy, and spontaneous abortion) and 2 of 15,067 placebo recipients (COVID-19, pneumonia, and acute respiratory distress syndrome in one participant and spontaneous abortion in the other one). No signs of vaccine-associated enhanced disease were observed. CONCLUSIONS: SCB-2019 administered as a 2-dose series has an acceptable safety profile. No safety concerns were identified during the 6-month follow-up after the primary vaccination. Clinical Trials Registration: NCT04672395; EudraCT: 2020–004272-17.