Heterologous ChAdOx1 and Bnt162b2 vaccination induces strong neutralizing antibody responses against SARS-CoV-2 including delta variant with tolerable reactogenicity

Neutralizing Activity Against SARS-CoV-2 Delta and Omicron Variants Following a Third BNT162b2 Booster Dose According to Three Homologous or Heterologous COVID-19 Vaccination Schedules

“…For the evaluation of neutralizing activities against the Omicron and Delta variants, we selected 170 sera from 75 participants of a nationwide multicenter prospective cohort (50 samples from 35 ChAd-ChAd-BNT participants, 60 samples from 20 ChAd-BNT-BNT participants, and 60 samples from 20 BNT-BNT-BNT participants) ( Bae et al., 2022 ). Details are presented in Supplementary Table S1 .…”

“…Similar to the Delta (B.1.617.2) variant that sparked the global COVID-19 outbreak in late 2021, Omicron escapes vaccine-induced immunity further via multiple mutations in key epitopes for neutralizing antibodies ( Andrews et al., 2022 ; Buchan et al., 2022 ; Gruell et al., 2022 ). In the Republic of Korea, nationwide COVID-19 vaccination using the BNT162b2 (BNT; Comirnaty, Pfizer/BioNTech, Mainz, Germany) or the ChAdOx1 (ChAd; Vaxzevria, to AstraZeneca, Oxford, UK) vaccines was implemented in early 2021 with three major homologous or heterologous two-dose vaccination schedules, including ChAd-ChAd, ChAd-BNT, and BNT-BNT, according to the vaccine-induced adverse events (especially severe reactogenicity and vaccine-induced immune thrombotic thrombocytopenia after ChAd) and vaccine supply ( Bae et al., 2021 ; Kim et al., 2021 ; Yang et al., 2021 ; Bae et al., 2022 ). From late 2021, individuals were encouraged to receive a 3rd dose of BNT to overcome the immune escape of Delta and Omicron.…”

Kinetics of vaccine-induced neutralizing antibody titers and estimated protective immunity against wild-type SARS-CoV-2 and the Delta variant: A prospective nationwide cohort study comparing three COVID-19 vaccination protocols in South Korea

“…This nationwide, multicenter, prospective cohort study was initiated under the leadership of the Korean Disease Control and Prevention Agency (KDCA) to evaluate the safety and efficacy of the national COVID-19 vaccination program. An earlier analysis of data from this study was published previously, which compared adverse effect and peak antibody response between the vaccination protocols (8). In the present analysis, we conducted a six-month follow-up analysis of the cohort.…”

“…Among them, BNT162b2, an mRNA vaccine developed by Pfizer and BioNTech (BNT), and AZD1222 ChAdOx1, an adenovirus-vectored vaccine developed by Oxford University and AstraZeneca (ChAd), were widely administered to the public (1,2). Both vaccines were initially designed for administration in two doses at three-(BNT) or four-(ChAd) week intervals (3,4), but vaccination strategies in South Korea have been amended several times because of serious vaccine-induced adverse effects and vaccine supplements (5)(6)(7)(8). Meanwhile, breakthrough infections were observed earlier than expected, mostly due to the rapid spread of the Delta variant (B.1.617.2) (9), which reduces vaccine-induced neutralizing activity by three-to four-fold (9)(10)(11)(12)(13)(14)(15)(16)(17).…”

“…In particular, an ability to accurately estimate protective immunity based on the kinetics of neutralizing antibody titers is essential for predicting the persistence of the protective effect after a third vaccine dose (19)(20)(21)(22). For this purpose, we investigated changes in the serologic response following vaccination using three major strategies implemented in South Korea: two doses of the BNT vaccine at a three-week interval (BNT group), two doses of the ChAd vaccine at a 12-week interval (ChAd group), and a single dose of ChAd followed by heterogeneous boosting with BNT at a 12-week interval (ChAd-BNT group) (8). For the estimation of protective immunity, we utilized the 20.2% of the mean PRNT titer of convalescent sera for 50% protective value as suggested by Khoury DS et al (23).…”