SARS-CoV-2 Variant Vaccine Boosters Trial: Preliminary Analyses (preprint)

Background: Protection from SARS-CoV-2 vaccines wanes over time and is compounded by emerging variants including Omicron subvariants. This study evaluated safety and immunogenicity of SARS-CoV-2 variant vaccines. Methods: This phase 2 open-label, randomized trial enrolled healthy adults previously vaccinated with a SARS-CoV-2 primary series and a single boost. Eligible participants were randomized to one of six Moderna COVID19 mRNA vaccine arms (50 mcg dose): Prototype (mRNA-1273), Omicron BA.1+Beta (1 or 2 doses), Omicron BA.1+Delta, Omicron BA.1 monovalent, and Omicron BA.1+Prototype. Neutralization antibody titers (ID50) were assessed for D614G, Delta, Beta and Omicron BA.1 variants and Omicron BA.2.12.1 and BA.4/BA.5 subvariants 15 days after vaccination. Results: From March 30 to May 6, 2022, 597 participants were randomized and vaccinated. Median age was 53 years, and 20% had a prior SARS-CoV-2 infection. All vaccines were safe and well-tolerated. Day 15 geometric mean titers (GMT) against D614G were similar across arms and ages, and higher with prior infection. For uninfected participants, Day 15 Omicron BA.1 GMTs were similar across Omicron-containing vaccine arms (3724-4561) and higher than Prototype (1,997 [95%CI:1,482-2,692]). The Omicron BA.1 monovalent and Omicron BA.1+Prototype vaccines induced a geometric mean ratio (GMR) to Prototype for Omicron BA.1 of 2.03 (97.5%CI:1.37-3.00) and 1.56 (97.5%CI:1.06-2.31), respectively. A subset of samples from uninfected participants in four arms were also tested in a different laboratory at Day 15 for neutralizing antibody titers to D614G and Omicron subvariants BA.1, BA.2.12.2 and BA.4/BA.5. Omicron BA.4/BA.5 GMTs were approximately one third BA.1 GMTs (Prototype 517 [95%CI:324-826] vs. 1503 [95%CI:949-2381]; Omicron BA.1+Beta 628 [95%CI:367-1,074] vs. 2125 [95%CI:1139-3965]; Omicron BA.1+Delta 765 [95%CI:443-1,322] vs. 2242 [95%CI:1218-4128] and Omicron BA.1+Prototype 635 [95%CI:447-903] vs. 1972 [95%CI:1337-2907). Conclusions: Higher Omicron BA.1 titers were observed with Omicron-containing vaccines compared to Prototype vaccine and titers against Omicron BA.4/BA.5 were lower than against BA.1 for all candidate vaccines. Clinicaltrials.gov: NCT05289037

Reactogenicity, Safety, and Serological and Cellular Immunogenicity of a Booster Dose of SARS-CoV-2 mRNA Prototype, Variant, and Bivalent Vaccines (preprint)

Waning immunity after two SARS-CoV-2 mRNA vaccinations and the emergence of variants precipitated the need for booster doses. We evaluated safety and serological and cellular immunogenicity through 6 months after a third mRNA vaccination in adults who received the mRNA-1273 primary series in the Phase 1 trial approximately 9 to 10 months earlier. The booster vaccine formulations included 100 mcg of mRNA-1273, 50 mcg of mRNA-1273.351 that encodes Beta variant spike protein, and bivalent vaccine of 25 mcg each of mRNA-1273 and mRNA-1273.351. A third dose of mRNA vaccine appeared safe with acceptable reactogenicity. Vaccination induced rapid increases in binding and neutralizing antibody titers to D614G, Beta, Delta and Omicron variants that persisted through 6 months post-boost, particularly after administration of Beta-containing vaccines. Spike-specific CD4 + and CD8 + T cells increased to levels similar to those following the second dose. Boost vaccination induced broad and durable humoral and T cell responses. ClinicalTrials.gov numbers NCT04283461 (mRNA-1273 Phase 1) and NCT04785144 (mRNA-1273.351 Phase 1)