Syringes filled with flu vaccine. (Jack Dempsey/Associated Press)

The world's first flu pandemic in a generation didn't quite develop the way health experts feared it might. The swine flu outbreak of 2009-2010 was fairly mild as major flu outbreaks go. Still, it raised a lot of awareness about getting flu shots.

A year later, it turned out that seasonal flu would be a force to be reckoned with. In early January, Health Canada was reporting a surge of cases in Quebec, Ontario and Manitoba. Ontario health officials said hospitals were running short on beds because a lot more patients were being admitted with complications from the flu.

Over the course of a normal flu season, one in 10 adults and one in three children will come down with the flu.

Health Canada says between 4,000 and 8,000 Canadians — mostly seniors — will die from pneumonia related to flu and many others may die from other serious complications of flu.

Still, flu awareness campaigns are helping Canadians stay healthier. Flu drugs such as Tamiflu and Relenza are easily available, although they can have their own dangers: 10 Canadians have died after taking Tamiflu, while at least 84 more have reported adverse reactions to the drug. On Nov. 29, 2006, Health Canada issued an advisory about reports of hallucinations and abnormal behaviour — including reports of self-harm — in patients taking Tamiflu.

Influenza is a highly contagious respiratory disease that strikes as many as eight million people in flu season, between October and April.

While flu and cold symptoms can be similar, influenza is much more serious because it drastically reduces the body's ability to fight off other infections.

There are two main kinds of flu viruses: influenza A, which can make you really sick, and B, which is usually milder.

Because flu viruses are unstable, an immune system exposed by infection or vaccine one year wouldn't recognize it was the same virus the following year.

That's why there's a new vaccine every year.

Flu shot safe, successful

While the flu shot is becoming increasingly important, critics note that it doesn't work all the time. It's 70 to 90 per cent effective in healthy adults. The success rate is somewhat lower in children and seniors. The shot is very safe, with certain specific exceptions. Those allergic to eggs shouldn't take it (the vaccine is produced in eggs), there may be short-lived side effects like a mild case of the flu, and one in a million people will develop Guillain-Barré Syndrome (GBS), a nervous system disease.

But most GBS patients recover, and the risk is small, compared with the havoc the flu wreaks, Health Canada's National Advisory Committee on Immunization says.

Some individuals who get the shot still get the virus, but it's usually a milder case than it would have been without the inoculation.

"Vaccination of people at high risk each year before the influenza season is currently the most effective measure for reducing the impact of influenza," the National Advisory Committee said in a 2003 report. And compared with sending someone to hospital, it's cheap, the Canadian Institute of Health Information (CIHI) says. "Having one senior hospitalized with influenza costs about the same amount (excluding physician costs) as giving 260 people flu shots."

The vaccine can reduce the proportion of elderly people who need to be hospitalized with pneumonia by 60 per cent, the Ontario Health Insurance Plan (OHIP) says.

Provincial priority

The provinces, which are responsible for delivering health-care initiatives, have made the flu shot a priority. For almost a decade, Ontario has made the flu shot available to everyone over the age of six months, at no charge. It was the first universal flu shot program in North America.

In 2008, 42 per cent of the population took advantage of the program. That's the highest immunization rate in Canada.

Ontario, the Yukon and the Northwest Territories are the only jurisdictions in Canada that make the shot freely available to all residents, while other jurisdictions provide the vaccine to the highest-risk groups.

Those include:

• Anyone over 65.
• Residents of long-term care facilities or nursing homes.
• People with serious chronic illnesses, such as cardiac or pulmonary disorders, asthma, diabetes, cancer and immunodeficiency conditions (including HIV); health-care workers.
• People with other chronic medical conditions that have lasted over six months.
• People on long-term aspirin therapy.
• Those traveling to destinations where influenza is prevalent.
• Anyone with household or work contacts with people in those categories.
• Children between the ages of six and 23 months.

Exceptions: anyone under six months of age or with severe egg allergies should not be vaccinated. Individual provinces are expanding the list of groups eligible for free shots, so some now include essential service workers, such as police officers and firefighters, while others have added people who share accommodations with high risk individuals.

The flu vaccine is made from inactivated viruses, grown in fertilized hens' eggs. After the shot, the immune system produces antibodies that attack the flu virus when it enters the body.

The flu shot:

• Should be taken every year, because the vaccine is updated to fight the latest strains of the virus.
• Should be taken between October and December, to give the body time to build resistance before the flu season starts.
• Takes a week or two to become effective and can last a year.

U.S. health authorities are also pushing flu shots. The American Academy of Family Physicians has recommended that universal influenza vaccinations start at age 50 because there are many high-risk individuals in the group between 50 and 65.