Abstract Objective: To evaluate immunological response to Covid-19 vaccines in immunocompromised haematology patients and compare with immunocompetent healthy controls Design: We compared total Anti SARS CoV 2 spike antibody and T cell response in 45 immunocompromised haematology patients with 30 healthy adults following 2 doses of Covid 19 vaccine for 3 to 5 months at 30 day intervals Setting: University Hospital, United Kingdom, Single Centre, March 2021 to December 2021 Main Outcome measures: Peak quantitative spike-specific antibody and cellular responses Results: We found 1. Non significant difference in T cell and total Anti SARS CoV 2 S antibody response between study and control group patients 2. Six (13%) study group participants did not have detectable Total Anti SARS Cov 2 S antibodies at any time point throughout the study monitoring period. 3. Three (7%) of the study group participants had no response, even after additional booster doses of Covid-19 vaccine. 4. All (100%) of the control group had detectable Anti SARS Cov 2 S antibodies after 2 doses of Covid 19 vaccine. 5. No participant died or was hospitalised due to severe Covid-19 infection during the study period. This included study group participants who had no antibody response at any time point. Conclusions: Though there was a non significant difference in T cell and total Anti SARS CoV 2 S antibody response between immunocompromised patients and healthy controls this did not result in any severe infection or Covid 19 related mortality in our study cohort. We did not identify any patient-specific factor (age, gender), specific haematological condition or treatment as determinant of response. Covid-19 vaccination was well tolerated without major side effects in both groups. What was already known about this topic: prior to starting this study there were no studies to confirm immunological response following Covid 19 vaccination in immunocompromised haematology patients. During the conduct of our study there have been publications from researchers confirming blunted serological response in 62-66% of immunocompromised haematology patients compared to 74 to 95% in healthy controls. What this study adds: Our study did not identify a significant difference in serological or T cell response between immunocompromised and healthy groups. Though 13% of immunocompromised patients had no response to Covid-19 vaccination none of them suffered from severe Covid-19 infection. We believe T cell response to Covid-19 vaccination has an important role in providing protective efficacy against Covid 19.

The authors have declared no competing interest.

This study is funded by the University Hospitals of North Midlands Research Charitable Fund. The study was sponsored by the Research and Innovation Directorate at University Hospitals of North Midlands.

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London Bridge Research Ethics Committee, reference 21/HRA/0304

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