Patients with hemato-oncological malignancies are among those at greater risk of a severe course if infected with COVID-19. Furthermore, immunization reduces response rates in hematological malignancies and lowers antibody levels in solid cancer patients. The effectiveness and safety of a heterologous booster immunization with Ad26.COV2.S DNA vector vaccine in hemato-oncological patients who had no antibody response following a double-dose BNT162b2 messenger (m-)RNA COVID-19 vaccine was examined by the researchers for a study. A total of 32 hemato-oncological non-responders to double-dose BNT162b2 were vaccinated with Ad26.COV2.S by heterologous booster immunization. Blood samples were collected both before (T0) and 4 weeks after immunization (T1). A predefined questionnaire was used to do the safety evaluation.

With a mean (SD) antibody titer of 693.79 (1 096.99) binding activity units (BAU)/ml, the total response rate was 31%. Patients with chronic lymphocytic leukemia or lymphoma had a decreased response rate (P = 0.048). Adverse effects were documented in 29.6% of patients, with 71% of them classified as serious, including grade III and IV occurrences according to the Common Terminology Criteria for Adverse Events (CTCAE). In 9 of the 29 patients who did not respond to double-dose BNT162b2, the heterologous booster immunization with Ad26.COV2.S resulted in a serological reaction. Furthermore, in the sample, the vaccine was safe, resulting in mostly minor local and systemic responses. Overall, the vaccine regimen should be studied further in order to improve response rates in the extremely sensitive population of hemato-oncological patients.