Profiling antibody epitopes induced by mRNA-1273 vaccination and boosters (preprint)

Characterizing the antibody epitope profiles of messenger RNA (mRNA)-based vaccines against SARS-CoV-2 can aid in elucidating the mechanisms underlying the antibody-mediated immune responses elicited by these vaccines. This study investigated the distinct antibody epitopes toward the SARS-CoV-2 spike (S) protein targeted after a 2-dose primary series of mRNA-1273 followed by a booster dose of mRNA-1273 or a variant-updated vaccine among serum samples from clinical trial adult participants. Multiple S-specific epitopes were targeted after primary vaccination; while signal decreased over time, a booster dose after >6 months largely revived waning antibody signals. Epitope identity also changed after booster vaccination in some subjects, with 4 new S-specific epitopes detected with stronger signals after boosting than with primary vaccination. Notably, the strength of antibody responses after booster vaccination differed by the exact vaccine formulation, with variant-updated mRNA-1273.211 and mRNA-1273.617.2 booster formulations inducing significantly stronger S-specific signals than a mRNA-1273 booster.

Quantifying the vaccine-induced humoral immune response to spike-receptor binding domain as a surrogate for neutralization testing following mRNA-1273 (Spikevax) vaccination against COVID-19 (preprint)

Background: There is a need for automated, high throughput assays to quantify immune response after vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study assessed the combined utility of the Roche assays, Elecsys(R) Anti-SARS-CoV-2 S (ACOV2S) and Elecsys Anti-SARS-CoV-2 (ACOV2N) using samples from the 2019-nCoV vaccine (mRNA-1273, Spikevax) phase 2 trial (NCT04405076). Methods: Samples from 593 healthy participants in two age cohorts (18-54 years and [≥]55 years), who received two injections with either placebo (n=198) or mRNA-1273 at a dose of either 50 [≥]g (n=197) or 100 [≥]g (n=198), were collected at Days 1 (first vaccination), 15, 29 (second vaccination), 43 and 57. ACOV2S results were used to assess the humoral response to vaccination in different clinical trial subgroups and were compared to a live virus microneutralization assay. Sample panels from patients with evidence of previous or concomitant infection (as identified using ACOV2N) or with an inconsistent antibody response pattern were analyzed separately. Results: Receptor-binding domain (RBD)-specific antibodies were readily detectable by ACOV2S for the vast majority of participants (174/189 [50 [≥]g dose group] and 178/192 [100 [≥]g]) at the first time point of assessment, with non-converters predominantly older in age. Complete seroconversion for all participants was observed at the subsequent timepoint (Day 29) and before administration of the second dose of vaccine. Two weeks after the first vaccine dose (Day 15), geometric mean concentration (GMC) of antibody levels were 1.37-fold higher in the 100 [≥]g compared with the 50 [≥]g dose group; this difference reduced to 1.09-fold two weeks after the second dose (Day 43). In both the 50 [≥]g and 100 [≥]g dose groups, a more pronounced response was observed in the younger versus the older age group on Day 15 (2.49-fold and 3.94-fold higher GMC, respectively) and Day 43 (1.35-fold and 1.50-fold higher GMC). Few subjects had a previous or concomitant natural SARS-CoV-2-infection (n=8). Vaccination of pre-infected individuals boosted the immune response to very high ACOV2S results compared to infection-naive vaccine recipients. ACOV2S measurements were strongly correlated with those from the live microneutralization assay (Pearson's r=0.779; p<0.0001) and good qualitative agreement was achieved (100% positive and 91.8% negative percentage agreement; 90.0% positive and 100% negative predictive value). Conclusion: The results from this study confirmed that ACOV2S is a highly valuable assay for the tracking of vaccine-related immune responses. Combined application with ACOV2N enables serologic monitoring for breakthrough infection or stratification of previous natively-infected individuals. The adaptive measuring range and high resolution of ACOV2S allows for the early identification of seroconversion as well as for resolution of very high titers and detection of longitudinal differences between age and dose groups. Additionally, good correlation of ACOV2S with live virus microneutralization indicates the utility of ACOV2S as a reliable estimate of neutralization capacity in routine diagnostic settings.

mRNA-1273 Vaccine-elicited Neutralization of SARS-CoV-2 Omicron in Adolescents and Children (preprint)

Background The highly transmissible severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) Omicron variant is a global concern. This study assessed the neutralization activity of two-dose regimens of mRNA-1273 vaccination against Omicron in adults, adolescents and children. Methods Neutralizing activity against the Omicron variant was evaluated in serum samples from adults ([≥]18 years) in the phase 3, Coronavirus Efficacy (COVE) and from adolescents (12-17 years) in the TeenCOVE trials following a two-dose regimen of 100 Background The highly transmissible severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) Omicron variant is a global concern. This study assessed the neutralization activity of two-dose regimens of mRNA-1273 vaccination against Omicron in adults, adolescents and children. Methods Neutralizing activity against the Omicron variant was evaluated in serum samples from adults ([≥]18 years) in the phase 3, Coronavirus Efficacy (COVE) and from adolescents (12-17 years) in the TeenCOVE trials following a two-dose regimen of 100 g mRNA-1273 and from children (6-<12 years) in the KidCOVE trial administered two doses of 50 g mRNA-1273. Neutralizing antibody geometric mean ID50 titers (GMT) were measured using a lentivirus-based pseudovirus neutralizing assay at day 1 and 4 weeks (day 57) following the second mRNA-1273 dose, compared with wild-type (D614G). Results At 4 weeks following a second dose of mRNA-1273 (100 g), the GMT was reduced 28.8-fold compared with D614G in adults ([≥]18 years). In adolescents (12-17 years), the GMT was 11.8-fold lower than D614G, 4 weeks after a second dose of mRNA-1273 (100 g), and compared with adults, were 1.5- and 3.8-fold higher for D614G and the Omicron variant, respectively. In children (6-<12 years), 4 weeks post-second dose of 50 g mRNA-1273, Omicron GMTs were reduced 22.1-fold versus D614G and were 2.0-fold higher for D614G and 2.5-fold higher for Omicron compared with adults. Conclusions A two-dose regimen of 100 g mRNA-1273 in adolescents and of 50 g in children elicited neutralization responses against the Omicron variant that were reduced compared with the wild-type D614G, and numerically higher than those in adults.

Booster of mRNA-1273 Vaccine Reduces SARS-CoV-2 Omicron Escape from Neutralizing Antibodies (preprint)

Data obtained on SARS-CoV-2 variant Omicron suggest that Omicron poses an increased risk of symptomatic breakthrough infections in people who receive only 2 doses of mRNA-1273. Administration of a booster mRNA vaccine may substantially reduce this risk.