Anaphylaxis is a serious systemic allergic reaction that is potentially life-threatening. Anaphylaxis has a rapid onset and requires immediate adrenaline administration. Guidance for anaphylaxis management post-vaccination can be found in the Australian Immunisation Handbook.

Diagnosis of anaphylaxis is based on clinical symptoms* and history of a recent exposure of a probable trigger (most commonly foods or drugs, but very occasionally, vaccination).

*Symptoms of anaphylaxis are:

  • difficulty or noisy breathing
  • swelling of the tongue
  • swelling or tightness in the throat
  • difficulty talking or a hoarse voice
  • wheeze or persistent cough
  • persistent dizziness or collapse
  • s young child becoming pale or floppy.

There are some laboratory investigations that may support a diagnosis of anaphylaxis. In the case of death, laboratory investigations may provide evidence towards a cause of death, including anaphylaxis.

Cells involved in anaphylaxis include mast cells and basophils, although though mast cells predominate. Upon activation of these cells, degranulation causes release of a range of mediators from inside the cell to the extracellular environment. The most well-studied mediators that are released from the cell are tryptase and histamine. In practice, histamine has limited value for investigation purposes.

Clinical presentations that can mimic anaphylaxis, but that do not usually result in raised tryptase levels include vasovagal reactions, septic shock or seizures.

Serum tryptase (also known as mast-cell tryptase) may be useful for ruling in anaphylaxis and so should be collected for all suspected cases, however it is much less useful in ruling it out.

Under what circumstances should a serum tryptase be collected?

The diagnosis of anaphylaxis is made based on clinical grounds. The majority of anaphylaxis secondary to the Pfizer – BioNTech (Comirnaty) COVID-19 vaccination occurs within 15 minutes of administration. Vaccine recipients who have a history of severe allergy will be observed for at least 30 minutes following vaccination.

Serum tryptase should be collected where anaphylaxis is clinically suspected.

Mediator: Tryptase

Timeframe and collection notes

  1. Collect an initial serum sample as soon as feasible, but do not delay initiating treatment. Collect in plain blood tube (= serum) without gel.
  2. Collect a second sample at 1-2 hours (but no later than 4 hours) from onset of symptoms.
  3. If possible, take an extra 5-10 mL for storage to facilitate further investigations.
  4. If there is likely to be a delay in analysis due to transport, then the sample should be frozen at -20⁰C. If the sample is to be processed on site, then freezing is not required.
  5. Post-mortem blood is also suitable, if the death did not occur within 30 minutes of the onset of symptoms. The interpretation of post-mortem tryptase levels can be more difficult than the interpretation of antemortem samples. Sample collection should occur from a peripheral site with the femoral artery clamped and collection should occur as soon as possible.

If further advice is required to support investigations following suspected anaphylaxis, the NSW Immunisation Specialist Service may be contacted for urgent advice on 1800 679 477.


Serious adverse events following immunisation (AEFI) are notifiable conditions in NSW. Healthcare providers are required to report any serious AEFI to NSW Health and the Therapeutic Goods Administration. More information is available on Adverse events following immunisation (AEFI).


NSW Public Health Unit (PHU)

*Make a mandatory AEFI report, or for advice on whether an event is notifiable.
1300 066 055 – key in the postcode of residence for the relevant public health unit
Operating hours: Monday to Friday 8:30am – 5pm

NSW Immunisation Specialist Service (NSWISS)

Advice on the investigation or clinical management of a serious AEFI
1800 679 477
Operating hours: Monday to Friday 9:00am – 5pm

After hours support NSWISS

*urgent advice on the clinical management of serious AEFI

Through the Children's Hospital Westmead switchboard: 02 9845 0000.

Current as at: Thursday 25 August 2022
Contact page owner: Immunisation