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The prevalence and mortality of COVID-19 are higher in patients with haematological malignancies (HM) compared to the general population (Vijenthira et al. 2020). Two SARS-CoV-2 messenger RNA (mRNA) vaccines have been approved by Swissmedic, both are highly efficient in preventing COVID-19 in the general population. The efficacy of these vaccines in patients with haematological malignancies remains unknown as immunocompromised patients have been excluded from the vaccine studies.
Initial reports on immunocompromised patients, such as solid organ transplant recipients, indicate a lower immunogenicity in immunocompromised hosts with only 11% to 17% having detectable anti-spike antibody 20-28 days after one vaccine dose (Boyarsky et al. 2021).

With regard to patients treated at the Cantonal Hospital St. Gallen, 7 of 66 myeloma-patients vaccinated against COVID-19 since January 2021 suffered from a COVID-19 infection despite having received one or two vaccinations against COVID-19. Two patients died. This indicates a clinically relevant suboptimal response to the current vaccines in at least a subgroup of patients with haematological malignancies. However, it is largely unknown, which kind of diseases and treatments are associated with a less effective vaccination response.

In general, in patients with haematological malignancies, the potential benefit of applying available anti-viral vaccines is considered to outweigh the risk (Cheuk 2011). However, there is clear evidence for an insufficiency of the respective vaccines in a variety of conditions. Especially B-cell depleting therapies and probably B-cell malignancies itself seem to weaken the humoral vaccination response (Sun et al. 2021). The anti-CD20 antibody Rituximab, widely used in the treatment of B-cell malignancies, has been shown to render vaccinations against Influenza A widely ineffective (Berglund et al. 2014). Hence, some medical societies recommend against influence-vaccinations during treatment with Rituximab (Rieger et al. 2018). However, B cell depletion may not preclude a cellular vaccination response totally: in a study regarding the efficacy of a recombinant varicella zoster (VZV) vaccine, 50% of patients who did not seroconvert showed a T-cell response against VZV (Zent et al. 2020). Anti-CD38-antibodies like Dara-tumumab are now widely used in the treatment of myeloma patients. Treatment with Daratumumab is known to alter the T-cell compartment in myeloma patients (Krejcik et al. 2016). Hence, T-cell responses after COVID-19-vaccination may be impaired as well during Daratumumab treatment. Of note, five of the seven of our patients with a COVID-19 infection after vaccination were treated with Daratumumab.