INTRODUCTION
Although approved vaccines have been rigorously tested for safety, anaphylactic reactions, albeit very rare, can occur1and potentially, any vaccine can cause an allergic reaction. According to the Institute of Medicine, epidemiologic and mechanistic evidence support a causal relationship between anaphylaxis and several vaccines, including those for measles, mumps and rubella (MMR), varicella, influenza, hepatitis B, meningococcus, human papillomavirus, and the combined diphtheria, tetanus, pertussis vaccine2. Of note, most cases of suspected allergy to a vaccine are not effectively confirmed in up to 85% of the patients referred for an allergy evaluation, and patients can continue vaccination with the same formulation and tolerance of the booster doses3.
An analysis of reported anaphylaxis to the Vaccine Adverse Event Reporting System (VAERS) in the United States over a 26-year period found that out of the almost 500,000 reports, only 828 were classified as anaphylaxis based either on physician’s diagnosis or in according to the Brighton Collaboration case definition4. Similarly, a 2016 study used health data from the Vaccine Safety Datalink and found altogether 33 confirmed cases of anaphylaxis after 25,173,965 vaccine doses and an anaphylaxis rate of 1.31 per million vaccine doses5. In children, Gold et al.6, demonstrated that only 10% of reported generalized allergic reactions developed a reaction on re-exposure and that most of these reactions were not suggestive for a hypersensitivity reaction.
Allergic reactions after vaccination can be due to any of the vaccine components such as microbial antigens, adjuvants, stabilizers, preservatives, emulsifiers, leached packaging components, residual antibiotics, cell culture materials and inactivating ingredients. Consequently, knowing all vaccine components is the starting point in evaluating the suspected adverse reaction.
In clinical practice we face two distinct situations which pose specific related challenges: I) children with a suspected allergic reaction to a vaccine: it is necessary to evaluate whether the reaction is allergic or not and how to manage the need to complete the immunization schedule; II) children with history of allergy to a vaccine component: it is necessary to assess the safety of administering that specific vaccine.
A correct management of suspected allergic reactions is crucial in terms of overall health care, both for the individual and for the community, constituting a potential risk of increased vaccine hesitancy, especially in light of that most of these patients are falsely labelled as allergic.
Aim of this review is to provide the means for a practical approach in the everyday clinical setting in regards to vaccines and allergy.