Vaccination in PADs.

Primary antibody deficiencies (PADs) are the most common primary immunodeficiencies (PIDs). They can be divided into the following groups, depending on their immunological features: agammaglobulinemia; common variable immunodeficiency (CVID) isotype; hyper IgM isotype; light chain or functional deficiencies with normal B cell count; specific antibody deficiency with normal Ig concentrations and normal numbers of B cells and transient hypogammaglobulinemia of infancy. The role of vaccination in PADs is recognized as therapeutic, diagnostic and prognostic and may be used in patients with residual B-cell function to provide humoral immunity to specific infective agents. According to their content and mechanisms, vaccines are grouped as live attenuated, inactivated (conjugated, polysaccharide), mRNA or replication-deficient vector vaccines. Vaccination may be unsafe or less effective when using certain vaccines and in specific types of immunodeficiency. Inactivated vaccines can be administered in PAD patients even if they could not generate a protective response; live attenuated vaccines are not recommended in major antibody deficiencies. From December 2020, European Medicines Agency (EMA) approved vaccines against COVID-19 infection: according to ESID advises, those vaccinations are recommended in patients with PADs. No specific data are available on safety and efficacy in PAD patients.