Federal authorities have not seen a huge number of adverse side-effects to a single shipment of H1N1 vaccine, since an early November batch that resulted in a higher-than-usual number of Canadians experiencing severe allergic reactions.
Health Canada reviews all batches of vaccine before it's shipped by the manufacturer to provinces and territories. Side-effects to vaccines are not uncommon and can range from severe allergic reactions to nausea, dizziness and headaches.
There were reports that one batch of vaccine, distributed over the week of November 2, caused more allergic reactions than normal. Six people had suffered from a severe allergic reaction in a batch that contained 172,000 doses, said Tim Vail, spokesman for the health minister. Anaphylaxis is a severe allergic reaction that can be characterized by respiratory distress, swelling of the lips, eyelids, throat or tongue, and low blood pressure, among other symptoms. All six Canadians have fully recovered.
The majority of the doses in batch 7A have been administered, federal officials say.
"People who have received the vaccine and have not had an allergic reaction have no reason to be concerned," a spokeswoman for the Public Health Agency of Canada said in a statement Tuesday. "The H1N1 flu virus vaccine has proven to be both safe and highly effective."
"The fact that we have identified a potential safety issue underscores that our monitoring system works."
As a precautionary step, Health Canada asked GlaxoSmithKline on Nov. 18 to instruct provinces who received the vaccine not to use any remaining doses, so they can investigate the higher-than-normal allergic reactions in Lot 7A. British Columbia, Alberta, Saskatchewan, New Brunswick, Ontario and Prince Edward Island received vaccine from that batch.
"Placing vaccine lots on hold is not an unusual occurrence. Over the past few years, Health Canada has placed specific lots of other vaccine on hold pending further investigation," the agency said yesterday.
Usually, there's one adverse reaction per 100,000 doses. In several lots, there have no reported adverse reactions to the vaccine.
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.
As of Nov. 7, 36 Canadians suffered serious side effects, including one death, out of 6.6 million doses. The death of an elderly person after receiving the H1N1 shot has not been conclusively linked to the vaccine and is currently being investigated.
More than 12 million doses of the vaccine have been distributed to provinces and territories, and another 3 million is flowing to jurisdictions this week as they open up flu clinics to healthy people.