IMMEDIATE RECTIONS
Immediate hypersensitivity reactions to vaccines are rare, with a
frequency that vary between 1 per 50,000 –1,000,000
doses7,8. They typically occur between a few minutes
and up to 4 hours after vaccination, and urticaria is the most frequent
manifestation occurring four times more frequently than
anaphylaxis9. Other skin reactions include erythema,
isolated pruritus and angioedema especially involving the face and lips.
Respiratory symptoms, such as rhinoconjunctivitis, sensation of throat
closure, dyspnoea and wheezing are less commonly
reported10.
Anaphylaxis is defined, according to EAACI11 as a
life-threatening reaction characterized by acute onset of symptoms
involving different organ systems and requiring immediate medical
intervention and, when suspected to be vaccine-related, has to be
evaluated according to the Brighton Collaboration Working Group Criteria
recently reviewed with emphasis on objective symptoms and
signs12. They define anaphylaxis as the involvement of
at least two organs and provide a combination of major and minor
criteria for classifying increasing levels of diagnostic certainty
differing from Sampson et al. anaphylaxis clinical criteria commonly
used in clinical settings.
Overall, being characterised by a broad range of possible symptoms, a
number of immediate adverse events following immunization could be
misdiagnosed as anaphylaxis and differential diagnosis and alternative
potential triggers has always to be considered whenever an episode
appears to coincide with vaccine administration13, see
Tab 1.
Since post-vaccination anaphylaxis is very rare, usually it starts to be
reported to passive pharmacovigilance during post-marketing surveillance
and data are often influenced by under- and over-reporting, incomplete
information and lack of denominators13. Recently,
Miller et al. assessed current VAERS sensitivity for anaphylaxis ranging
from 13% to 76%14, that highlights the need of a
correct diagnostic framework performed by allergists or immunologists
expert in vaccine allergy for a correct vaccination management. Being
rare, the incidence varies among different studies: in a study
population consisted of children and adolescents Bohlke et
al.15 reported 5 cases of anaphylaxis after
administration of 7,644,049 vaccine doses, for a risk of 0.65
cases/million doses; while, McNeil et al.5 identified
18 cases of anaphylaxis after administration of 12,403,201 vaccine doses
to 0-17 age group, for an incidence rate of 1.45 cases per million
vaccine doses.
Treatment of anaphylaxis in the setting of vaccine administration is
reviewed in Castells et al.16.
Although rare, the precise diagnostic management of a suspected
anaphylaxis post-vaccination is of paramount importance due to the risk
of a potential serious reactions after re-exposure and, not secondly,
because of overdiagnosis of severe allergic reactions to vaccines might
lead to an increase in the number of children that interrupt
vaccinations, resulting in an individual and collective risk of loss of
protection against immune preventable diseases.