Myocarditis and pericarditis after immunization: Gaining insights through the Vaccine Adverse Event Reporting System

Aim: To characterize cases of myocarditis (MC) and pericarditis (PC) recorded in the Vaccine Adverse Event Reporting System (VAERS). Methods: Cases were extracted from VAERS (2011–2015) and assessed for causality using standardized WHO algorithm. Disproportionality analysis was performed through reporting odds ratio (ROR) with 95%CI. MEDLINE was also searched. Results: In VAERS, 199 cases of MC or PC were collected, among which 149 reported smallpox vaccine. The remaining were: 15 cases in ‘YOUNGER GROUP’ (YG; <18 years old) and 35 in ‘OLDER GROUP’ (OG; >18 years old). Main reported vaccines were against Human Papilloma Virus (n = 6) in YG and influenza (n = 16) in OG. Causality always resulted “undeterminate” for YG, whereas either “undetermined” (30 cases) and “correlated” (3 cases) for OG. Statistically significant ROR was found in YG for meningococcal vaccine (ROR = 3.55; 95%CI = 1.23–10.24) and in OG for thyphoid vaccine (11.13; 7.73–16.03), Japanese encephalitis vaccine (8.54; 2.7–27.01), anthrax (25.5; 18.8–34.5), and, as expected, smallpox (71.88; 49.25–104.89). In MEDLINE, 91 articles were found: positive/possible causality was frequently reported. Conclusions: MC and PC after immunization appear extremely rare; only in very few cases can a role of vaccine be actually identified. Signals for vaccines against typhus, Japanese encephalitis, anthrax and meningococcus warrant monitoring.