Changes in serum-neutralizing antibody potency and breadth post-SARS-CoV-2 mRNA vaccine boost

Three immunizations with Novavax's protein vaccines increase antibody breadth and provide durable protection from SARS-CoV-2

The immune responses to Novavax's licensed NVX-CoV2373 nanoparticle Spike protein vaccine against SARS-CoV-2 remain incompletely understood. Here, we show in rhesus macaques that immunization with Matrix-MTM adjuvanted vaccines predominantly elicits immune events in local tissues with little spillover to the periphery. A third dose of an updated vaccine based on the Gamma (P.1) variant 7 months after two immunizations with licensed NVX-CoV2373 resulted in significant enhancement of anti-spike antibody titers and antibody breadth including neutralization of forward drift Omicron variants. The third immunization expanded the Spike-specific memory B cell pool, induced significant somatic hypermutation, and increased serum antibody avidity, indicating considerable affinity maturation. Seven months after immunization, vaccinated animals controlled infection by either WA-1 or P.1 strain, mediated by rapid anamnestic antibody and T cell responses in the lungs. In conclusion, a third immunization with an adjuvanted, low-dose recombinant protein vaccine significantly improved the quality of B cell responses, enhanced antibody breadth, and provided durable protection against SARS-CoV-2 challenge.

Systematic review and meta-analysis of the factors affecting waning of post-vaccination neutralizing antibody responses against SARS-CoV-2

Mass COVID-19 vaccination and continued introduction of new SARS-CoV-2 variants increased prevalence of hybrid immunity at various stages of waning protection. We systematically reviewed waning of post-vaccination neutralizing antibody titers in different immunological settings to investigate differences. We searched published and pre-print studies providing post-vaccination neutralizing antibody responses against the Index strain or Omicron BA.1. We used random effects meta-regression to estimate fold-reduction from months 1 to 6 post last dose by primary vs booster regimen and infection-naïve vs hybrid-immune cohorts. Among 26 eligible studies, 65 cohorts (range 3-21 per stratum) were identified. Month-1 titers varied widely across studies within each cohort and by vaccine platform, number of doses and number of prior infections. In infection-naïve cohorts, the Index strain waned 5.1-fold (95%CI: 3.4-7.8; n = 19 cohorts) post-primary regimen and 3.8-fold (95%CI: 2.4-5.9; n = 21) post-booster from months 1 to 6, and against Omicron BA.1 waned 5.9-fold (95%CI: 3.8-9.0; n = 16) post-booster; Omicron BA.1 titers post-primary were too low to assess. In hybrid-immune, post-primary cohorts, titers waned 3.7-fold (95%CI: 1.7-7.9; n = 8) against the Index strain and 5.0-fold (95%CI: 1.1-21.8; n = 6) against Omicron BA.1; post-booster studies of hybrid-immune cohorts were too few (n = 3 cohorts each strain) to assess. Waning was similar across vaccination regimen and prior-infection status strata but was faster for Omicron BA.1 than Index strains, therefore, more recent sub-variants should be monitored. Wide differences in peak titers by vaccine platform and prior infection status mean titers drop to non-protective levels sooner in some instances, which may affect policy.