Background: Humoral and cellular immune responses to SARS-CoV-2 vaccines wane with time. In the COV‑ADAPT cohort, we recently studied both immunological components and their interdependencies following different vaccine combinations before (T1) and up to three months after second immunization (T2). This follow-up investigated the stability of long-term immune responses and aimed to identify predictive markers. Methods: We assessed humoral (anti-spike-RBD-IgG, neutralization capacity, avidity) and cellular (spike-induced T-cell interferon‑γ release) immune responses three-seven months after secondary vaccination (T3) in blood samples of 318 healthcare workers with previous homologous ChAdOx1 nCoV-19 (ChAdOx1), homologous BNT162b2 or heterologous ChAdOx1/BNT162b2 vaccinations. Results: At T3, homologous ChAdOx1 vaccination resulted in significantly lower anti-spike-RBD-IgG (152±151 BAU/ml) as compared to heterologous ChAdOx1/BNT162b2 (388±300 BAU/ml) and homologous BNT162b2 (435±327 BAU/ml). In all groups, anti-spike-RBD-IgG (T3) exceeded antibody levels before second vaccination (T1). T-cell interferon-γ release following heterologous ChAdOx1/BNT162b2 vaccination was significantly higher at T3 (1062±2083 mIU/ml) vs. T1 (680±1691 mIU/ml), yet did not differ significantly between the three groups at T3. Associations between humoral and cellular responses were found at T3 (all groups combined). Additionally, the early cellular response (at T1) was significantly associated with late (T3) humoral (ChAdOx1/BNT162b2, BNT162b2/BNT162b2) and cellular responses (all groups). In contrast to T2, neutralization capacity at T3 was significantly higher for ChAdOx1/BNT162b2 and BNT162b2/BNT162b2 vs. ChAdOx1/ChAdOx1. Conclusions: We identified (i) long-term interdependencies between the humoral and the cellular immune system, (ii) observed distinct waning dynamics following different vaccination regimes, and (iii) uncovered early T-cell responses as a useful predictor of long-term immune responses.
Background: Homologous and heterologous SARS-CoV-2 vaccinations yield different spike protein-directed humoral and cellular immune responses. This study aimed to explore their currently unknown interdependencies. Methods: COV-ADAPT is a prospective, observational cohort study of 417 healthcare workers who received vaccination with homologous ChAdOx1 nCoV-19, homologous BNT162b2 or with heterologous ChAdOx1 nCoV-19/BNT162b2. We assessed humoral (anti-spike-RBD-IgG, neutralizing antibodies, avidity) and cellular (spike-induced T cell interferon‑γ release) immune responses in blood samples up to 2 weeks before (T1) and 2 to 12 weeks following secondary immunization (T2). Results: Initial vaccination with ChAdOx1 nCoV-19 resulted in lower anti-spike-RBD-IgG compared to BNT162b2 (70±114 vs. 226±279 BAU/ml, p<0.01) at T1. Booster vaccination with BNT162b2 proved superior to ChAdOx1 nCoV-19 at T2 (anti-spike-RBD-IgG: ChAdOx1 nCoV-19/BNT162b2 2387±1627 and homologous BNT162b2 3202±2184 vs. homologous ChAdOx1 nCoV-19 413±461 BAU/ml, both p<0.001; spike-induced T cell interferon-γ release: ChAdOx1 nCoV-19/BNT162b2 5069±6733 and homologous BNT162b2 4880±7570 vs. homologous ChAdOx1 nCoV-19 1152±2243 mIU/ml, both p<0.001). No significant differences were detected between BNT162b2-boostered groups at T2. For ChAdOx1 nCoV-19, no booster effect on T cell activation could be observed. We found associations between anti-spike-RBD-IgG levels (ChAdOx1 nCoV-19/BNT162b2 and homologous BNT162b2) and T cell responses (homologous ChAdOx1 nCoV-19 and ChAdOx1 nCoV-19/BNT162b2) from T1 to T2. Additionally, anti-spike-RBD-IgG and T cell response were linked at both time points (all groups combined). All regimes yielded neutralizing antibodies and increased antibody avidity at T2. Conclusions: Interdependencies between humoral and cellular immune responses differ between common SARS-CoV-2 vaccination regimes. T cell activation is unlikely to compensate for poor humoral responses.