The most common adverse events of vaccines are fever, local pain or irritation, and local redness or swelling, which are not signs of allergy
With live vaccines, adverse effects can be delayed until 7 to 21 days after immunization; this includes vaccine-induced delayed-onset urticaria, which is commonly mistaken for allergy.
Assessment and allergy-focused clinical history
- Testing appropriate for all, whether anaphylaxis, mild symptoms, unknown history or family history.
- Gold standard is an oral challenge with a therapeutic dose of amoxicillin, 1hr observation, then 5 day course at home to ensure no delayed reaction.
- Low risk individuals, where IgE mediated reaction unlikely, can go direct to challenge without testing.
- Puncture and intradermal skin testing is recommended where reaction was within last 12 months, or there were respiratory symptoms.
- Skin testing using only penicilloyl-polylysine, with at least 5 mm of wheal and flare greater than wheal as the criteria for a positive test result, is now sufficient to rule out a high risk of having anaphylaxis during a confirmatory oral amoxicillin challenge
Egg is used in the manufacture of a number of vaccines. Whether this is clinically significant or not depends on the vaccine and the severity of the allergy:
- MMR – only contraindication is anaphylaxis to MMR or other constituent of MMR vaccine
- Influenza – (live nasal or inactivated injectable) patients with “severe anaphylaxis” (ie requiring intensive care) should be vaccinated in hospital.
- Varicella, Rabies – no contraindication for egg allergy
- Yellow fever – discuss with specialist if egg allergy
Gelatine (derived from pork or beef) can be a cause of allergic reactions esp MMR, Varicella, Japanese encephalitis. Allergy would usually be established from history of food reactions eg gummy/jelly sweets, marshmallows.
Latex – can be present in syringe or bung. See Latex allergy.
Despite these potential causes of allergy, immunisation can often be achieved through graded administration.
Some reports of persistent itchy nodules at injection site due to aluminium delayed hypersensitivity.