Vaccine use in primary immunodeficiency disorders.

Primary immunodeficiency disorders (PIDs) are a heterogeneous group of rare, congenital and genetically determined conditions caused by one or more defects of innate and/or adaptive immunity. In subjects suffering from PIDs, an unusually increased susceptibility to infections is demonstrated. As infections condition the final prognosis of most PIDs, clearly defined prophylactic practices are essential. In most cases, intravenously or subcutaneously administered immunoglobulin remains the mainstay of treatment, although antibiotics and antifungals can be added under some conditions, particularly when the infections are highly recurrent despite immunoglobulin replacement. Vaccines could also play a role, but their administration leads to different results depending on the type of PID: in some cases, immune response is not impaired, and vaccines can evoke the same protection as that usually induced in healthy subjects; in others, the immunodeficiency significantly interferes with antigen stimulation of the immune system and, depending on the type and degree of impairment, little or no protection is evoked. Moreover, particularly when live vaccines are given, significant vaccine-related adverse events can occur, including the emergence of disease from vaccine strains. The main aim of this paper is to discuss what is currently known about how and when vaccines can be used in patients with PIDs in order to facilitate physician choices and assure the best possible patient protection.