Effectiveness of COVID-19 vaccination in people with blood cancer

Problem

Blood cancer patients are at high risk of severe COVID-19 outcomes and were prioritised for COVID-19 vaccination in the UK. However, compared with the general population, people with haematological malignancies are known to have poorer response to COVID-19 vaccination, indicated by antibody and cellular responses. The aim of this study was to assess the effectiveness of COVID-19 vaccination against severe COVID-19 outcomes in people with blood cancer.

Approach

We analysed individuals with blood cancer aged ≥12 years on 1st December 2020 in the QResearch UK primary care database. The outcomes were COVID-19-related hospitalisation, ICU admission and mortality. We used a matched case-control design, matching on age, sex and calendar time, to estimate odds ratios (ORs) for outcomes in vaccinated versus unvaccinated blood cancer patients using conditional logistic regression models, adjusted for body mass index, ethnicity, deprivation, comorbidities and previous SARS-CoV-2 infection. We incorporated dose number and time since vaccination to investigate the level of protection afforded by booster doses and vaccine waning, and conducted stratified analysis across time periods when Alpha, Delta and Omicron BA.1 SARS-CoV-2 variants were dominant. We also compared vaccine effectiveness in blood cancer patients who received chemotherapy during the study period to those who did not.

Findings

The analysis included 81,793 people with blood cancer. During the study period, 1740 blood cancer patients experienced COVID-19-related hospitalisation, of whom 97 were admitted to the ICU, and 1119 died from COVID-19. For the primary course of vaccination, blood cancer patients were most protected against COVID-19 hospitalisation 2-6 weeks after the second dose (OR 0.43 [95% confidence interval (CI) 0.24-0.76] compared to unvaccinated) but after 26 weeks, vaccine effectiveness had waned (OR 1.01 [95%CI 0.74-1.39] 182-272 days after second dose compared to unvaccinated). Across all doses, vaccine effectiveness against COVID-19 hospitalisation was highest 2-6 weeks after the third dose, and remained high up to 14 weeks after the third dose (OR 0.35 [0.24-0.50] 14-41 days and OR 0.37 [95%CI 0.28-0.49] 42-97 days after third dose compared to unvaccinated). The likelihood of COVID-19 hospital admission 2-6 weeks after the fourth dose was lower than in unvaccinated individuals (OR 0.70 [95%CI 0.47-1.04]), but effectiveness was not as high as after the second or third doses. Preliminary results suggest there is heterogeneity in vaccine effectiveness across time periods when different SARS-CoV-2 variants were dominant, and that COVID-19 vaccines were less effective in those who received chemotherapy during the study period compared to those who didn’t.

Consequences

The preliminary results of this analysis suggest that COVID-19 vaccines are effective in blood cancer patients, but protection against COVID-19 hospitalisation starts to decline after approximately six weeks. Analyses of COVID-19 ICU admission and mortality outcomes, in different blood cancer types and comparisons against the general population are ongoing.