CD4 and Down syndrome: In February 2021, Spanish health authorities recommended prioritizing vaccination for patients at risk of severe disease from SARS-CoV-2 infection: solid organ transplant recipients, hematopoietic stem cell transplant (HSCT) recipients, patients with chronic kidney disease on hemodialysis, patients with combined primary immunodeficiencies, oncology patients undergoing chemo- or radiotherapy, individuals with HIV and CD4 < 200 cells/μL, patients with Down syndrome, and those receiving immunosuppressive or immunomodulatory therapies [1,2,3].