Adverse events following immunization in patients with primary immunodeficiencies.

Background: Adverse events following immunization (AEFI) requires special consideration in patients with primary immunodeficiency diseases (PID) because they may represent a "red flag" for the initial diagnosis and may cause disease complications. Therefore, the definition of appropriate vaccination schemes is a major issue in PID. The aim of this study is to describe the AEFI in a cohort of PID patients.

Methods: Medical records from 379 PID patients were included. AEFI severity was classified according to the WHO 1999 guidelines. Causality was assessed using the Clinical Immunization Safety Assessment (CISA) 2009 criteria.

Results: Evidence of AEFI was found in 26 medical records and represented a total of 29 reactions. Most of the AEFI were observed in patients with idiopathic hypogammaglobulinemia (IHG), chronic granulomatous disease (CGD) and severe combined immunodeficiency (SCID), representing 10, 4 and 4 cases, respectively. A total of 21 reactions were associated with replicative vaccines, 7 of which were serious cases related to Bacille Calmette-Guérin (BCG). BCG was also the vaccine more often associated with definitive AEFI in PID. In addition to BCG-related complications, seizures were the most serious AEFI among PID patients.

Conclusions: Our study included a large cohort of PID patients and confirmed an increased risk of serious AEFI in these populations. The design and implementation of neonatal screening strategies for the early detection of congenital lymphopenias and other PID are urgently needed to avoid serious complications of the BCG vaccine usually applied immediately after birth. Our findings also support the use of the acellular pertussis vaccine to minimize the appearance of seizures in PID patients vaccinated with diphtheria, pertussis and tetanus (DPT).