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.