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.