Surveillance of adverse events following immunization with meningococcal group C conjugate vaccine: Tuscany, 2005-2012

Introduction: Post-licensure vaccine safety studies are essential to identify uncommon events that may be difficult to assess during pre-licensure studies. The aim of our study was to evaluate the safety of serogroup C meningococcal conjugate (MCC) vaccine in Tuscany from 2005 to 2012. Methods. All adverse events (AEs) to MCC vaccine notified from 2005 to 2012 were obtained from the regional health authority. Results: Following 451,570 doses administered, 110 suspected AEs were notified (mean annual reporting rate: 2.8/10,000 doses). The most frequently AE reported was fever (60%), followed by swelling at the injection site (11%) and febrile seizures (10%). Overall, 77.3% of cases were not severe, while 21.8% required hospitalization. Almost four months after the receipt of the vaccine, a one-year-old infant was diagnosed with a pervasive developmental disorder with disturbance of speech, but any link with the vaccinations received was refuted. Most AEs (80.9%) occurred after co-administration with other vaccines, especially with MMR or MMRV vaccines (42.7%) or the DTPa-HBV-IPV/Hib vaccine (33.7%). Discussion: Our study confirmed the high level of safety of MCC vaccine in Tuscany: AEs proved rare and all cases had only temporary and self-resolving consequences. As usually only the most severe suspected AEs are reported, the true proportion of AEs requiring hospitalization was most probably overestimated, and it is plausible that most of these cases were in fact only temporally related.