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Allogeneic transplant recipients (HCT) remain at high risk of adverse outcomes from COVID-19 and emerging variants. The optimal prophylactic vaccine strategy for this cohort is not defined. T-cell mediated immunity is a critical component of graft-versus-tumour effect and in determining vaccine immunogenicity. Using validated anti-spike IgG and spike specific IFNγ ELISpot assays we analysed response to a two-dose vaccination schedule (either BNT162b2 or ChAdOx1) in 33 HCT recipients ≤2 years from transplant, alongside vaccine matched healthy controls (HC). After two vaccines, infection naïve HCT recipients had a significantly lower rate of seroconversion compared to infection naïve healthy controls (25/32 HCT vs 39/39 HC no responders) and had lower spike specific T-cell responses. HCT Patients who received BNT162b2 had a higher rate of seroconversion compared to ChAdOx1 (89% versus 74%) and significantly higher anti-S IgG titres (p = 0.022). Spike specific T cell responses were seen after one vaccine in HC and HCT patients. However, two vaccines enhanced spike specific T-cell responses in HC but not in the majority of HCT patients. These data demonstrate limited immunogenicity of two-dose vaccination strategies in HCT recipients, bolstering evidence of the need for additional boosters and /or alternative prophylactic measures in this group.

Original publication




Journal article


British journal of haematology

Publication Date



Peter Medawar Building for Pathogen Research Nuffield Department of Medicine; University of Oxford; Oxford, OX1 3SY;, United Kingdom.