Canada has identified an additional half-million flu shots it could purchase to try to meet a soaring late-season demand for the product.

However the deputy head of the Public Health Agency of Canada admits the country may still run out of vaccine, if people in Central and Eastern Canada follow the lead of Western Canadians and rush to get flu shots.

The unexpected surge has caught health officials across the country off guard, coming at a time when vaccine clinics would normally be winding down. With manufacturers now busy producing flu shots for the upcoming Southern Hemisphere winter, there is limited additional supply to buy.

The original Canadian order, placed in early 2013, was for 10.4 million doses. In many years, a purchase of that size would have left tens and even hundreds of thousands of doses unused. Last year, for instance, doctors and clinics in British Columbia returned 90,000 unused doses to the province at the end of the season.

Perplexingly, last year's flu season was harsher than this year's — or at least from what can be seen to date. But the main strain this year, H1N1, can hit young and middle-aged adults very hard. Reports of people in that demographic being hospitalized, placed in intensive care and occasionally even dying have received heavy media coverage.

That has spiked the public's perception of risk, experts suggest. Add to that word of potential vaccine shortages, and Canada is seeing the flu shot equivalent of a run on the bank.

"The key here is that this is a normal flu season," Dr. Gregory Taylor, Canada's deputy chief public health officer, stressed in an interview Friday.

"This issue is not because of increased disease. This issue is because of increased demand."

Taylor said he and his provincial and territorial counterparts met via a teleconference earlier in the day to bring each other up to speed. "We went through jurisdiction by jurisdiction. Other than some tiny variabilities, this is a normal flu season."

The level of flu activity may be normal, but the demand for flu vaccine is off the charts, at least in some parts of the country.

Alberta, Saskatchewan and the Northwest Territories are nearing the end of their supplies. The latter two jurisdictions said Friday they will reserve the remaining vaccine for people most likely to get seriously ill if they catch the flu.

Saskatchewan is restricting flu vaccinations to children under five, pregnant women and women who have just given birth while the Northwest Territories will give priority to pregnant women and children under five.

Quarter million doses on the way

Taylor said Canada's vaccine supply working group — a federal, provincial and territorial committee — is working hard to try to match vaccine need with remaining supply — a task that sounds about as complex as like running air traffic control at a busy international airport after a winter storm.

An extra 245,800 doses of vaccine are being purchased from the suppliers who contract with the federal government to provide it each season, Taylor said.

GlaxoSmithKline, Sanofi Pasteur and Novartis supply vaccine for the federal, provincial and territorial flu vaccine programs. Their contracts stipulate they must hold aside an additional five per cent on top of their total order in case Canada needs to buy more vaccine — an option being exercised this year. As well, AstraZeneca — the maker of FluMist, a vaccine puffed into a nostril — is providing 157,000 doses, Taylor said, adding that figure is part of the 245,800 total.

Some of the additional stock is available now, and more will be delivered in the next few weeks, he said. The provinces and territories agreed Friday to a plan for divvying up the extra product, and Ontario and Quebec have offered to loan vaccine to Saskatchewan until the new purchases can be delivered, he added.

Canada is also exploring the possibility of purchasing another 360,000 doses that were made for other customers but not purchased by them. But Taylor said a decision on whether it will be bought — or needed — hasn't been made yet.

The potential mismatch between demand and supply underscores the difficulty public health officials face trying to figure out how much flu vaccine to purchase each year.

While the federal government bulk buys Canada's supplies of flu vaccine to get a better price, provinces and territories are responsible for determining how much they need, and for paying for their portion of the total purchase.

(The federal government buys a small amount of vaccine — around 60,000 doses — for the Canadian Armed Forces, the RCMP, and for First Nations people on reserves in Alberta. In all other jurisdictions First Nations people receive flu vaccine through the provincial or territorial programs.)

Vaccine order 'complicated'

Provinces and territories must submit orders months in advance. For this flu season orders were placed in February 2013, said Dr. Perry Kendall, B.C.'s chief medical officer of health. That far ahead of time health ministries had no way of knowing if the flu season would be mild, severe or somewhere in between.

The amount of vaccine administered in previous years is used to help gauge the need for a coming year. The goal is to have enough vaccine for everyone who wants it, but not to waste taxpayers' money by throwing away large quantities of unclaimed flu shots.

"It is really very complicated and very prone to factors that you really have no control over," said Kendall.

Last year between seven to nine per cent of B.C.'s purchase went unused "which is higher than we'd like to see," he said.

"Obviously you'd like to be more accurate, but you're running a fine line. Because you don't want to under-order but neither do you want to over-order. Because 90,000 doses is about half a million dollars' worth of vaccine."

Luckily for B.C. residents, the province didn't trim its order for the 2013-14 season. In fact, it increased its buy to 1.4 million from 1.3 million doses in 2012-13. Even at that, while the province still has vaccine, some pharmacies and clinics are out, Kendall said.