CD4 and HIV infectious disease: Rituximab, which has been shown to effectively prevent attacks in NMOSD, is used for the treatment of HIV-related B cell lymphoma; however, there is an increased risk of infections, especially for patients with low CD4+ T-cell counts.7 In addition, the humoral immune response to vaccinations is reduced in patients receiving rituximab, which is a considerable aspect of therapeutic management in the context of the COVID-19 pandemic.3 Besides B cell depletion, HIV infection and low CD4 cell counts can be considered as additional risk factors that diminish vaccination efficacy.