Adverse events following immunization: real causality and myths

ABSTRACT

Introduction: To assure the highest safety of immunization programs, detect adverse events following immunization (AEFIs), eliminate concerns, and reduce the risk of low vaccination coverage, authorities in industrialized countries have collected years of reports of suspected AEFIs and have systematically assessed their clinical importance.

Areas covered: In this paper, the methods used to assess vaccine safety and the results obtained by the analysis of reports, studies, and meta-analyses are discussed.

Expert opinion: Severe AEFIs are rare, and all evaluations of safety of vaccines recommended for both children and adults have demonstrated that the advantages of vaccines are always significantly higher than the problems that they cause, and there is no need to modify recommendations. However, the definition of AEFI is dependent on the vaccines themselves, complicating the definition of an AEFI and explaining why doubts and concerns have been raised. Presently, disease epidemiology data collected in healthy people and in subjects with underlying disease, general vaccine coverage, and the vaccination status of subjects with AEFIs are managed by many independent institutions. Only strict co-operation between these institutions will lead to the successful identification of AEFIs and to a reduction of the weight of anti-vaccine arguments.

KEYWORDS:

• adverse event
• AEFI
• immunization
• prevention
• reactogenicity
• tolerability
• vaccine

Article Highlights

• Vaccines are widely recognized as one of the most successful and cost-effective public health interventions, significantly reducing the morbidity and mortality of a variety of infectious diseases.

• Severe adverse events after vaccination occur more frequently in subjects with underlying clinical conditions, although in some cases they can occur in otherwise healthy children.

• For several years, in most industrialized countries, official authorities have collected reports of suspected AEFIs and have systematically assessed their real clinical importance.

• Although the assessment of vaccine safety extends to all phases of the development of individual vaccine preparations, post-licensure surveillance is an essential adjunct to pre-licensure activities.

• Four categories of AEFIs are considered: the first includes those for which evidence convincingly supports a causal relationship; the second includes those for which data favor acceptance of a causal relationship; the third includes those for which evidence favors the rejection of a causal relationship; and the fourth includes those for which data are inadequate to accept or reject a causal relationship.

• Severe AEFIs are rare, and all the evaluations of the safety of immunization schedules recommended for both children and adults have found that the advantages of vaccines are always significantly higher than the problems they can cause and that there are no true problems that justify the modification of recommendations.

• All health-care workers must highlight the incredible advantages of vaccines.

This box summarizes key points contained in the article.

Declaration of interest

This paper was supported by Italian Ministry of Health (Bando Giovani Ricercatori 2009 GR-2009-1596786). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed