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faq

FAQ

About Allergy >
Pre-vaccination Screening Service >


About Allergy
1. Q: What is Allergy and how does it differ from intolerance?
  A: Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances. Intolerances can mimic allergies (sometimes referred to as pseudo-allergy) but it does not involve the immune system.
     
2. Q: What is mechanism for allergies?
  A: Allergies are caused by the presence of specific IgE antibody in the body directed to allergens. These antibodies bind to mast cells that are present in the lining of the lung, gastrointestinal tract and skin. When the cell bound IgE meets with an allergen the mast cell releases a series of very powerful chemicals, including but not limited to histamine, that cause the allergic symptoms.
     
3. Q: How to diagnose food allergy?
  A: Food allergy can be diagnosed by skin prick test or blood test together with a history of reaction shortly after eating the food. The gold standard for diagnosis is a food challenge.
     
4. Q: How to diagnose food intolerances?
  A: Food intolerance is usually diagnosed from a history of developing symptoms after eating – sometimes hours later. The recording of detailed food diaries can help, followed by dietary elimination and food re-introduction with/without food challenges.
     
5. Q: What is food challenge?
  A: Food challenge involves giving suspect foods to patients in a carefully graded and supervised manner every 15-30 minutes until symptoms appear or a predefined dose is reached.
     
6. Q: What is anaphylaxis?
  A: Anaphylaxis is a severe form of allergic reaction and results in a drop in blood pressure, asthma, throat swelling with difficulty in breathing, abdominal pains, skin rashes and collapse. It is an emergency and requires immediate administration of adrenaline. The common causes of anaphylaxis are foods and drugs.
     
7. Q: Is allergy inherited?
  A: The risk for developing allergies is greater if there is a family history of allergies. However there is no certainty that if parents have allergies then their child will definitely also have the problems.
     
8. Q: What are differences between skin prick tests, intradermal tests and patch tests?
  A: Skin prick tests are used for diagnosis of inhaled and ingested food allergies (e.g. pollens, cat, house dust mite, milk, egg, nuts). Intradermal tests are used mainly for drug allergies and bee/wasp venom allergies. Patch tests are used to diagnose causes of contact dermatitis. Skin prick and intradermal tests generally take a few minutes to perform, while patch testing requires a few days for a full assessment.
     
9. Q: What is FENO and the mannitol test?
  A: FENO stands for fractional expired nitric oxide and its concentration is measured in the air you breathe out. It reflects the degree of eosinophilic inflammation in the airways. The higher is the level the more severe the inflammation. It is a non-specific test for conditions such as asthma. The FENO is very sensitive to inhaled steroid therapy so when the drug improves the degree of airways inflammation the FENO level will come down.

Mannitol test is a specific inhalation test for asthma and the more sensitive you are to the test, the more airways inflammation you have and the more severe is your asthma. Similar to FENO mannitol test results will improve as your asthma improves.

Thus by monitoring your symptoms; lung function tests; FENO; and mannitol, the doctor can manage and treat your asthma very well.
     
10. Q: What is desensitisation?
  A: Desensitisation is a technique to allow a sufferer to be less allergic to specific substances, e.g. pollens, house dust mite or foods. There are two major approaches: by subcutaneous injection or by the oral route of the allergen. Oral route involves either sublingual administration or by ingesting the food (if it is food allergy). The general principle is to have an induction phase when the allergen is given slowly and regularly over several months to reach a maintenance dose. The maintenance dose is then administered on a regular basis for 3 years.
     
11. Q: Is desensitisation safe?
  A: Yes it is safe but side effects can occur, so the treatment has to be supervised by experienced specialists and conducted in an environment which can treat any allergic problems immediately if they arise.
     
12. Q: Are steroids safe?
  A: Long term use of steroid ointments and pills will cause side effects but most patients use too little rather than too much for fear of possible problems. This behaviour often results in poor resolution of the inflammation and may mean using more steroids in the medium term than would have been the case if the problem had been treated properly at the start. Your doctor will advise.



Pre-vaccination Screening Service
1. Q: What is the purpose of the COVID-19 pre-vaccination service?
  A: The Pre-vaccination Screening Service aims to help enhance vaccine safety for those are at high risk for severe allergic reaction associated with injection of a COVID-19 vaccine, especially with a history of drug or vaccine allergy.
     
2. Q: What is vaccine allergy?
  A: Similar to foods or drugs, people can be allergic to vaccines, but it is very rare. Allergic symptoms to vaccines range from hives to anaphylaxis.
     
3. Q: What are the likely causes for allergic reactions related to COVID-19 vaccines?
  A: The cause of the severe allergy following COVID-19 vaccination is unknown and there is no precedent as these mRNA vaccines are new. Historically, reactions to other vaccines are seldom caused by the active ingredients. Instead, inactive ingredients, such as the excipients polyethylene glycol (PEG) and polysorbates added to improve solubility, are the commonest causes of reactions. Over recent years, excipients have been recognised as hidden allergens that may be causing repeated reactions in patients with hitherto undiagnosed severe allergic reactions to multiple classes of drugs.
     
4. Q: What do I need to do for COVID-19 pre-vaccination screening?
  A: You will be required to complete a questionnaire to evaluate your history of drug/ vaccine allergy. Depending on your level of risk you will undergo a series of tests, including skin prick and/or intradermal injections of diluted and safe doses of substances containing excipients commonly used in vaccines.
     
5. Q: How long does this COVID-19 Pre-vaccination screening service take?
  A: Since you will need to be assessed by our allergist before and to be observed after the testing, please allow 2 to 3 hours for this service.
     
6. Q: Will I know which vaccine is more suitable for me after pre-vaccination screening?
  A: The service will advise patients under what circumstances they can have their first injection containing a particular excipient, and/or their second injection if they had experienced a reaction after their first dose.
     
7. Q: Can I get the COVID-19 vaccine injection on the same day of the Pre-vaccination screening service?
  A: The Pre-vaccination Screening Service aims to help enhance vaccine safety for those are at high risk for severe allergic reaction associated with injection of a COVID-19 vaccine, especially with a history of drug or vaccine allergy. It is advisable to receive the pre-vaccination screening days ahead.

Separate bookings for Pre-vaccination Screening Service and the Government’s COVID-19 Vaccination Programme have to be done separately by you. For details of the territory-wide COVID-19 Vaccination Programme, please visit: (https://www.covidvaccine.gov.hk/en/programme)