As Canadian health officials assured the public that the pandemic H1N1 vaccine is as safe as the seasonal flu shot, at least one province is reporting almost double the rate of severe allergic reactions.
British Columbia Centre for Disease Control said it is probing why residents suffered anaphylaxis at a higher rate compared with the previous five seasonal-flu-vaccination programs, suggesting it could be because some people received H1N1 and the seasonal flu shot simultaneously.
It will be several more weeks before B.C. officials can definitively attribute the spike in the rate – 2.2 per 100,000 doses distributed, compared to 1.2 per 100,000 doses. None of the 18 anaphylaxis reactions in B.C. resulted in death.
“It would be fair to say that as more people are vaccinated in the weeks and months ahead, and more data are collected, the rates of adverse events per 100,000 may change both in B.C. and nationally,” said Roy Wadia, spokesman for the British Columbia Centre for Disease Control.
So far, no other province has reported higher rates of anaphylaxis – a severe, whole-body allergic reaction that can be characterized by respiratory distress, swelling of the lips, eyelids, throat or tongue, and low blood pressure, among other symptoms.
New Brunswick said it had one case of anaphylaxis in the 150,000 doses administered, while Manitoba, Alberta and Saskatchewan all reported rates of serious side effects that are comparable to previous years of providing seasonal flu shots. The Ontario health ministry said the province has had nine serious reactions but could not say how many of those were due to severe allergic reactions.
Canada's top public health doctor stressed Tuesday that the H1N1 shot is safe – only 36 Canadians have suffered serious side effects, including one death, out of 6.6-million doses as of Nov. 7.
The death of an elderly person after receiving the H1N1 shot has not been conclusively linked to the vaccine and is currently being investigated, said David Butler-Jones, the country's chief public health officer. It's possible, he said, that the person had an underlying medical condition.
“Canadians can be assured that, to date, the frequency of serious reactions is less than 1 per 100,000 doses distributed, which is what we've seen with other vaccines,” said Dr. Butler-Jones. “The benefit of immunization, the prevention of serious illness and death far outweigh any theoretical risk associated with being immunized.”
Overall, the rate of serious adverse events from the H1N1 vaccine has been trivial: 0.54 per 100,000 doses. The main side effects include allergic reaction, fever and convulsions. Allergic reactions have been reported at immunization clinics, although not as serious as anaphylaxis. Other more common mild effects, such as nausea, dizziness and headaches have also been reported.
The news of the vaccine's safety was revealed as many cities across the country looked to expand vaccinations to the general public in their fight against a virus that has killed about 200 Canadians.
“It's important to remember that just because a medical event follows vaccination, it may not have been caused by the vaccine,” Dr. Butler-Jones said. “It may have been caused by other factors, as unfortunate events continue to occur with or without vaccine.”
Andrew Simor, head of microbiology and infectious diseases at Sunnybrook Health Sciences Centre in Toronto, said the serious reactions to the H1N1 vaccine are comparable to the safety profile of many vaccines commonly used today.
“Of all the millions of doses of the H1N1 vaccine administered worldwide,” Dr. Simor said, “there have been very few side effects, demonstrating an excellent safety profile.”
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