Study assesses the risk of adverse events after revaccination in patients with suspected vaccine allergy

Study assesses the risk of adverse events after revaccination in patients with suspected vaccine allergy

Patients who experience a post-immunization adverse event (APV) may lose confidence in the safety of the vaccine, which ultimately reduces the acceptance of subsequent vaccinations. When a patient develops more serious conditions, such as anaphylaxis or seizures, it is difficult, in fact, both for the patient himself and for the health professionals, in receive and indicate, respectively, a next vaccine. Although AEFIs are generally specific to a particular immunizer, safety concerns can extend to different types.

The occurrence of allergic events such as immediate or delayed-type hypersensitivity symptoms (such as rash, urticaria, angioedema, and serum sickness-like reactions) after vaccination often raises specific concerns among clinicians and patients regarding the potential for a serious event. with subsequent exposure to the vaccine. Allergy skin testing is an important tool in diagnosing immediate hypersensitivity. However, it is not standardized for most vaccines and false positive and negative results can occur.

Given this difficulty, researchers from Canada conducted a study whose objective was precisely to estimate the risk of AEFI recurrence after revaccination and to determine, among patients with suspected vaccine allergy, whether a positive skin test was associated with the recurrence of these events. The study was published in Journal of Pediatrics.

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The study performed was prospective and observational, including patients evaluated in the Canadian Special Immunization Clinic Network (SIC) from June 2013 to September 2019 with AEFI who required revaccination with the vaccine temporally associated with their event.

After consent, patients were referred to the SIC Network due to at least one of the following AEFI:

  • Fever (temperature equal to or greater than 40.5° Ç;
  • Local reaction equal to or greater than 10 cm in diameter;
  • Cellulitis, abscess, nodule, or Arthus reaction at the injection site;

According to the Brazilian Society of Immunizations (SBIM), the Arthus reaction (or grade III hypersensitivity reaction)) is characterized by aIntense local inflammatory action on the skin, mediated by complexes formed by the binding of antigens with antibodies.

  • Allergic-type event within 24 hours after vaccination or delayed-type hypersensitivity symptoms;
  • Persistent crying lasting three hours;
  • seizure or other neurological event;
  • Hypotonic-hyporesponsive episode;
  • arthralgia or arthritis;
  • Thrombocytopenia;
  • Other unexpected or exceptionally serious and worrisome AEFIs.

Clinicians used guidelines to inform their recommendations. Participants underwent standardized assessment and data collection and were followed up after revaccination to capture recurrences. Finally, the data were transferred to a central bank for descriptive analysis.


In total, 588 participants were evaluated for 627 AEFIs. Of these, 570 (91%) occurred in pediatric patients under 18 years of age.

AEFIs included:

  • Immediate hypersensitivity (130/627; 21%);
  • Extensive local reactions (110/627; 18%);
  • Non-urticarial rash (51/627; 8%);
  • Seizures (26/627; 4%);

There were 61 neurological events, including 13 (21%) febrile seizures, 13 (21%) afebrile seizures, 5 (8%) Guillain-Barré syndrome/Miller-Fisher syndrome, and 30 (49%) other neurological AEFIs (myelitis, encephalitis, paresthesia, developmental regression, stroke, optic neuritis, Bell’s palsy, cerebelitis). Twenty-two neurological events (36%) were serious.

  • Thrombocytopenia (11/627; 2%).

Revaccination was recommended for 513 of 588 (87%) participants. Among participants recommended for revaccination during the study period, 63% (299/477) were revaccinated.

The recurrence of AEFI was:

  • 10% (31/299) overall;
  • 31% (15/49) for extensive local reactions;
  • 7% (5/66) for immediate hypersensitivity;
  • There was no recurrence of other neurological events among eight revaccinates.

No recurrence was serious. Among 92 participants with suspected vaccine allergy who had a skin test and were revaccinated, the negative predictive value (NPV) of the skin test for AEFI recurrence was 96%.


The researchers noted that the majority of patients with prior AEFI can be successfully recommended revaccination as the risk of recurrence of severe AEFI is low, particularly for patients with low to moderate impact AEFI such as extensive local reactions, immediate hypersensitivity and seizure. .

Allergy skin test NPV for recurrence of these events is high, although most patients with positive skin tests can also be safely revaccinated in controlled settings.

The results of this study can enrich discussions about the safety of revaccination after an AEFI and support the harmonization of approaches to ensure that patients can be optimally protected against vaccine-preventable diseases.

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