ABSTRACT
Patients undergoing treatment for haematological malignancies have been shown to have reduced antibody responses to vaccination against SARS-COV2. This is particularly important in patients who have undergone allogeneic haemopoietic stem cell transplantation (HSCT), in whom there is limited data about vaccine efficacy. In this retrospective single-centre analysis, we present data on serologic responses following one, two, three or four doses of either Pfizer-BioNTech (PB), AstraZeneca (AZ) or Moderna (MU) SARS-CoV- 2 vaccines from a series of 75 patients who have undergone allogeneic HSCT within 2 years from the time they were revaccinated. The seroconversion rates following post-HSCT vaccination were found to be 50.7%, 78%, 79% and 83% following the first, second, third and fourth primary post -HSCT vaccine doses, respectively. The median time from allograft to first revaccination was 145 days (range 79-700). Our findings suggest that failure to respond to the first SARS-CoV- 2 vaccine post-HSCT was associated with the presence of acute GVHD (p = 0.042) and treatment with rituximab within 12 months of vaccination (p = 0.019). A statistical trend was observed with the presence of chronic GVHD and failure to seroconvert following the second (p = 0.07) and third (p = 0.09) post-HSCT vaccine doses. Patients who had received one or more SARS-CoV- 2 vaccines prior to having an allogeneic stem cell transplant were more likely to demonstrate a positive antibody response following the first dose of revaccination against Sars-CoV- 2 (p = 0.019) and retained this seropositivity following subsequent doses. The incidence of confirmed COVID-19 diagnosis among this cohort at the time of analysis was 16%. 17% of these were hospitalised and there was one recorded death (8%) secondary to COVID-19 in a patient who was 15.7 months post allogeneic transplant. In summary, this study suggests that despite the initial low seroconversion rates observed postallogeneic transplant, increasing levels of antibody response are seen post the second primary vaccine dose. In addition, there seems to be lower risk of mortality secondary to COVID-19 in this vaccinated population, compared to what was reported in the earlier phases of the pandemic prior to use of SARS-COV2 vaccination. This adds support to the widely adopted policy of early full revaccination with repeat of primary vaccine doses and boosters post-HSCT to reduce mortality in this population. Finally, we have identified rituximab use and active GVHD as potential risk factors influencing serological responses to SARS-COV2 vaccination and further work should focus on further characterising this risk and optimum dosing schedule both pre-and post-transplant.