Switzerland, which had also suspended use of the vaccines last week, followed suit. And it was reported that even Italy, which was the first in a chain of countries to halt use of the Novartis vaccines, is now reviewing its decision.
In fact, a senior official of Health Canada admitted the regulatory body might never have put a hold on the products if it had had details last week about why its Italian counterpart had blocked delivery of Novartis vaccines in that country.
Health Canada was finally able to get that information from Italy on Tuesday, and also used other sources of data to conduct a risk assessment on the products, sold in Canada under the brand names Fluad and Agriflu.
It turned out that Italy had taken the action based solely on a report from the company that it had found one batch of vaccine made at its Siena, Italy, plant that contained a higher-than-normal level of protein aggregates.
Novartis pulled that batch from the distribution pipeline. Protein aggregates — which are tiny pieces of the killed viruses used to make flu vaccine — were not seen in other lots of the vaccines made at Siena, the company has said.
"Once we confirmed that the information that the Italian regulator had made its decision on was the same as that which we got from Novartis and the same that the Swiss had got, then we felt comfortable with the decision," Dr. Paul Gully, Health Canada's senior medical adviser, said in an interview.
"If we had reassured ourselves very quickly that we were all working from the same information, then yes, it is likely that we would never have been in this situation."
Switzerland's drug safety agency Swissmedic said in a release Wednesday that it had placed a hold on use of Novartis flu vaccines after Italian health authorities reported there might have been contaminants found in the products.
But the agency said it was persuaded the visible particles were not external contaminants, but rather bits of viral proteins.
The proteins are a critical component of the vaccine. They provoke the immune system to create antibodies that should protect the recipient from catching the flu. Normally the proteins in flu vaccine are in a suspension and are not visible to the naked eye. But from time to time they fall out of suspension and can be seen.
It is not uncommon, nor is it a sign that there is something wrong with the vaccine, Dr. Vas Narasimhan, the global head of vaccines development for Novartis Vaccines and Diagnostics, told The Canadian Press earlier this week.
The company welcomed Health Canada's decision that the vaccines are safe for use.
"We were convinced, of course, even during the assessment because we had our internal quality controls. And this external assessment from Health Canada just confirmed what we believed already," said Dr. Riad Sherif, president of Novartis Canada.
Sherif said Novartis had already shipped about three-quarters of the vaccines it was contracted to supply to provinces and territories, and the remainder will go out in the next few days.
Novartis is providing vaccine to all provinces as well as the Northwest Territories, though some jurisdictions are slated to get more of the Novartis product than others.
Saskatchewan is getting much of its product from Novartis this year and its flu shot delivery efforts were badly disrupted by the halt-use order. The province's chief medical officer of health said it may take a little time to get those efforts back into gear.
"Some of the larger clinics, of course, will need a day or two to ramp up," said Dr. Saqib Shahab. "Because while the clinics were suspended, staff were busy doing other things and were allocated to do other routine public health work as well."
Even provinces that don't rely as heavily on the Novartis vaccines may see an impact from the incident. Infectious diseases specialists are worried the suspension of use of the Novartis vaccines, even though it was temporary, may further shake public confidence in flu shots.
"On the one hand it shouldn't be a big deal, but it may very well be a big deal," said Dr. Michael Gardam, head of infection control at Toronto's University Health Network.
Gardam suggested the timing was bad for flu shot campaigns, coming at a time when public health is trying to get people to roll up their sleeves and hospitals in a number of parts of the country are exploring the idea of making flu shots mandatory for health-care workers.
"There's a pretty strong anti-vaccination sentiment out there, both inside and outside of health care," Gardam said. "And it doesn't take much to get people upset and worried that the vaccine isn't safe.
"So something like this, no matter how many times you try to explain that this is a pretty common phenomenon and it doesn't really mean anything, people go 'Yeah, but they recalled it.'"
The Novartis vaccines make up a total of 20 per cent of Canada's combined flu vaccine purchase this year. GlaxoSmithKline has the lion's share of the national purchase, 57 per cent. Sanofi Pasteur and AstraZeneca make up the rest, with 20 per cent and three per cent respectively.
Health Canada's statement announcing the lifting of the suspension said the department and the Public Health Agency of Canada will work with Novartis to monitor the safety and effectiveness of the vaccines.
"Should a safety concern be identified, immediate and appropriate action will be taken," it said.
The Public Health Agency of Canada is advising people who administer flu shots to allow the vaccine to come to room temperature before use. They also say the products should be shaken and checked for any white floating material before they are injected, though they added that material is not uncommon and doesn't pose a health risk.