ABSTRACT
The progression of the COVID-19 pandemic leads to the emergence of variants of concern (VOC), which may compromise the efficacy of the currently administered vaccines. Antigenic drift can potentially bring about a reduced protective T cell immunity and consequently to more severe disease manifestations. To assess this possibility, the T cell responses to the wild-type, Wuhan-1 SARS-CoV-2 ancestral spike protein and Omicron B.1.1.529 spike protein were compared. Accordingly, peripheral blood mononuclear cells (PBMC) were collected from 8 healthy volunteers 4-5 months following a third vaccination with BNT162b2, and stimulated with overlapping peptide libraries representing the spike of either the ancestral or Omicron SARS-CoV- 2 virus variants. Quantification of the specific T cells was carried out by a fluorescent ELISPOT assay, monitoring interferon-gamma (IFNg), interleukin-10 (IL-10) and interleukin-4 (IL-4) secreting cells. For all the examined individuals, comparable level of reactivity to both forms of spike protein were determined. In addition, a dominant Th1 response was observed, manifested mainly by IFNg secreting cells and only limited numbers of IL-10 and IL-4 secreting cells. The data demonstrates a stable T cell activity to the emerging Omicron variant in the tested individuals, therefore the protective immunity to the variant following BNT162b2 vaccination is not significantly affected.
ABSTRACT
rVSV-{Delta}G-SARS-CoV-2-S is a clinical stage (Phase 2) replication competent recombinant vaccine against SARS-CoV-2. Nonclinical safety, immunogenicity and efficacy studies were conducted in 4 animal species, using multiple dose levels (up to 108 PFU/animal) and various dosing regimens. There were no treatment related mortalities in any study, or any noticeable clinical signs. Compared to unvaccinated controls, hematology and biochemistry parameters were unremarkable and no adverse histopathological findings gave cause for safety concern in any of the studies. There was no viral shedding in urine, nor viral RNA detected in whole blood or serum samples 7 days post vaccination. The rVSV-{Delta}G-SARS-CoV-2-S vaccine immune response gave rise to neutralizing antibodies, cellular immune response, and increased lymphocytic cellularity in the spleen germinal centers and regional lymph node. No evidence for neurovirulence was found in C57BL/6 immune competent mice or in highly sensitive IFNAR KO mice. Vaccine virus replication and distribution in K18 hACE2 transgenic mice showed a gradual clearance from the vaccination site with no vaccine virus recovered from the lungs. The rVSV-{Delta}G-SARS-CoV-2-S vaccine was well tolerated locally and systemically and elicited an effective immunogenic response up to the highest dose tested, supporting further clinical development.