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All along, allergic reaction symptoms have been mentioned as posible flu vaccine side effects, usually in the context of flu vaccines being "safe". For example, government authorities might say that flu vaccines cause only mild side effects... including allergic reactions.
To the man in the street, an allergic reaction to flu shot might bring to mind symptoms such as rashes, or some slight swelling at the injection spot, which seem harmless enough. But call the reaction "anaphylaxis" and it starts to sound alarming.
It is alarming. At end-November 2009, reports came from Canada about an abnormally high rate of anaphylaxis following H1N1 vaccination. On 26 November, the Public Health Agency of Canada (PHAC) confirmed 24 cases of anaphylaxis, including one death.
GlaxoSmithKline, the vaccine manufacturer, has withdrawn a batch of its vaccine and the vaccination programme is continuing as investigations are underway. The withdrawn lot of vaccines, comprising 170,000 doses, was shipped to several Canadian provinces. However, it was not used in Quebec, where a man in his 80s died from the severe allergic reaction symptoms.
The "normal" rate of such allergic reaction symptoms is said to be 0.32 in 100,000. Initial reports in Canada put the rate at 4 in 100,000. But this was based on initial reports that only six people suffered anaphylaxis, out of over 150,000 vaccine doses given out from the affected batch. With 24 confirmed cases now, the true incidence of anaphylaxis in Canada is actually alarmingly higher - about 16 in 100,000!|
Anaphylaxis symptoms
Anaphalaxis may be triggered by various substances including foods, insect stings, drugs and vaccines. Severe allergic reaction symptoms usually develop quickly, within minutes of exposure to the allergen. If not treated immediately, the affected person may lose consciousness and die. Severe allergic reaction symptoms would be medically classified as anaphylaxis if they affect at least two of these organ systems - skin, heart and stomach. Common symptoms include: Breathing: wheezing, shortness of breath, swollen tongue or throat that causes breathing difficulties, chest pain / tightness, nasal congestion, etc. The person may also have cough, hoarse voice, or itchy mouth / throat. Heart / Blood Circulation: weak pulse, rapid heartbeat, poor blood circulation causing the skin to turn pale / blue, low blood pressure resulting in dizziness, light-headedness, fainting and loss of consciousness. Skin: rashes, hives, swelling, itch, redness and feelings of warmth. Digestion: nausea, vomiting, diarrhea and abdomen pain / cramps. Others: anxiety, feelings of “impending doom,” itchy / red / watery eyes, headache and uterus cramps. |
It is still not known what caused the higher rates of severe allergic reaction symptoms in Canada. But not surprisingly, Canada's head of PHAC, Dr. David Butler-Jones, was quick not to blame the death case on the flu vaccine, but to point out that the person had other medical conditions. This has been the typical response whenever an adverse event follows a flu shot.
“It's important to remember that just because a medical event follows vaccination, it may not have been caused by the vaccination; it may have been caused by other factors, as unfortunate events continue to occur with or without vaccine," Dr Butler-Jones told a news conference.
He added that the severe allergic reactions symptoms were not related to the adjuvant that is added to boost the vaccine’s potency. Immune adjuants in flu vaccines are banned in the US due to safety concerns, but not in Canada, Europe and elsewhere.
Dr Bulter-Jones also warned that a large proportion of the population is still susceptible to the virus, estimating that half the population of Canada are at risk of falling ill with the virus.
Vaccine manufacturer GlaxoSmithKilne would only say that investigations being undertaken by itself, Health Canada and the PHAC "have not been completed."
Allergic reaction symptoms can always be expected from drugs and vaccines. In an interview with the Canadian press, Dr John Treanor, a flu vaccine expert at the University of Rochester, New York said:
"Any time you immunize somebody with something, there's always a chance of an allergic reaction. Some people are going to have anaphylaxis, absolutely."
Dr Treanor added that he rate of anaphylactic reactions will vary depending on the type of vaccine used and the age of the people the vaccine is being given to.
It can even vary by location. One study showed that Australia saw higher than expected rates of anaphylaxis when it rolled out its HPV vaccine campaign (against cervical cancer) - about 2.6 cases per 100,000 shots.
Anaphylaxis can be triggered by a wide variety of substances (see box story). And as vaccines are complex drugs made from many different ingredients, it can be hard to pinpoint the cause.
Most flu vaccines are produced in eggs and if there was residual egg protein, this can trigger allergic reaction symptoms in people with egg allergies. Most vaccines also contain antibiotics, which are another possible cause of allergic reactions.
But as to why one batch of vaccine might produce more allergic reaction symptoms than others, which was what happened in Canada, Dr Treanor says that is a difficult question to answer: "It's hard for me to think of what the mechanism would be for a lot-specific increase in anaphylactic reactions. The only thing that would make sense if it was really true that you were seeing with a specific batch that there were more anaphylactic reactions that there's something in that batch that's not in the other batches . . . that people tend to be allergic to."