TORONTO - The investigation into whether a batch of H1N1 vaccine may have triggered a higher-than-normal rate of allergic reactions hasn't yet come up with answers, vaccine manufacturer GlaxoSmithKline said Tuesday.
And health officials in Quebec said they are still trying to determine if the death of an elderly man who died of anaphylaxis after receiving a pandemic flu shot was triggered or hastened by the vaccination.
"Investigations being undertaken by GSK, Health Canada and the Public Health Agency of Canada (PHAC) have not yet been completed," GSK spokesperson Megan Spoore said in an email about the pulled batch of vaccine.
The lot, No. A80CA007A, comprised 172,000 doses of vaccine that were shipped last month to British Columbia, Alberta, Saskatchewan, Manitoba, Ontario and Prince Edward Island.
Quebec did not receive vaccine from the batch under investigation.
After discussions with Health Canada, which regulates vaccines, GSK told provinces last week not to use any more doses from this lot after it came to light that six cases of anaphylaxis had been reported in people who had H1N1 shots from the batch.
The event is raising a lot of questions. Here are some answers:
Q: What is anaphylaxis?
A: Anaphylaxis is a severe allergic reaction that in extreme cases can lead to death. Marked by sudden onset, the reaction can produce hives, cardiovascular problems and swelling of the tissues in the mouth and airways that can compromise breathing.
True anaphylaxis has to meet an internationally accepted diagnostic criterion called the Brighton collaboration case definition. It must involve at least two organ symptoms - in other words, some combination of reactions involving the skin, heart and respiratory systems.
Q: What causes anaphylaxis?
A: Anaphylaxis is an allergic response to exposure to an allergen, a non-pathogenic (i.e. not a germ or a fungus) substance that's capable of triggering a response from the immune system. For some people, pollen is an allergen. For others, peanut protein is.
Why some people are allergic to some things and others are not isn't clear. But when a person with an allergy encounters the specific allergen, his or her immune system generates a type of antibodies that trigger the release of histamines into their system, says Dr. Scott Halperin, a vaccine expert at Dalhousie University. Histamines induce the response.
Q: How is anaphylaxis treated?
A: True anaphylaxis is treated with epinephrine (adrenaline). That's the stuff in EpiPens carried by people with life-threatening allergies.
Q: Are there any doses of this suspect batch of vaccine left?
A: By the time GSK issued the halt-use order last week, all but about 20,000 doses of the batch had been used, a spokesperson for the Public Health Agency of Canada says.
Q: So that's about six cases of anaphylaxis out of about 152,000 shots given. Is that unduly high?
A: GSK said in a statement Tuesday that the expected rate of anaphylactic reactions to flu shots is in about one in 100,000.
Q: Is anaphylaxis a reaction seen with other vaccines or just flu shots.
A: "Any time you immunize somebody with something, there's always a chance of an allergic reaction," says Dr. John Treanor, an influenza vaccine expert at the University of Rochester in New York.
And if you vaccinate millions? "Some people are going to have anaphylaxis, absolutely," Treanor says.
Halperin says the 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. Australia saw higher than expected rates of anaphylaxis when it rolled out its HPV vaccine campaign - about 2.6 cases per 100,000 shots, according to one study. But those elevated rates weren't seen in North America.
Q: Why do some people have allergic reactions to vaccines?
A: "For most times people have anaphylaxis, you don't know exactly what it is. And vaccine is a complex mixture," Halperin says.
Most flu vaccine - and all the flu vaccine used in Canada - is produced in eggs. If there was residual egg protein in the vaccine it could trigger an allergic response in people with egg allergies, he says.
With the combined measles, mumps and rubella vaccine, reactions have occurred that are believed to be due to an antibiotic that is used in the production process, Halperin says.
Q: Why would one batch of vaccine produce more reactions than others?
A: Treanor says that's 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," he says.
"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."
