Why it's been such a tough flu season for children

More children are ending up in hospital for flu-related illnesses as two types of influenza hit Canada at once, according to a new report. 

This week's FluWatch report from the Public Health Agency of Canada says that overall flu activity is at its peak levels.

Several flu viruses are circulating, including a type called influenza B that tends to hit children hard. 

"Pretty much everywhere, influenza B is a really big player and it has been for a while, which is unusual for this time of year," said Dr. Michael Gardam, an infectious disease physician and chief of staff at Humber River Hospital in Toronto.

In Ontario, for instance, influenza A infections generally occur first in November and end by March. That's when influenza B ramps up. But this year has been a double whammy, with both influenza A and B circulating at the same time.

Stan Pollard's daughter, Layna Vu-Pollard, died of influenza B in Guelph, Ont. on Jan. 31. She was 12.

"The vision of her staring at you when you're trying to rescue your daughter's life is buried in your memory for the rest of your life," he told CBC Kitchener-Waterloo earlier this week. 

Pollard called 911 and performed CPR but said he regrets not being better aware of the warning signs of a fatal flu infection.

The U.S. Centers for Disease Control and Prevention (CDC) lists emergency warning signs for flu in children on its website; they include difficulty breathing, fast breathing, fever with a rash, and irritability, among others.

Emergency rooms overwhelmed

Influenza B does tend to cause more severe disease in children, said Dr. Allison McGeer, medical director of infection prevention and control at Mount Sinai Hospital in Toronto.

"We have a lot of trouble with flu because it's very common and it's complication rates are low," she said.

"From my perspective, one of the frustrating things is that when you talk about meningitis, everybody sits up, everybody pays attention, people get the vaccine in a heartbeat. But you're actually more likely to die from influenza."

In Nova Scotia, emergency rooms are reporting being overwhelmed, said Dr. Todd Hatchette, a medical microbiologist and infectious disease physician at Dalhousie University in Halifax.

"The bed pressures are more significant this year than they have been in the last couple," he said.

Two factors contribute to the intensity of a flu season:

• The virulence or deadliness of a particular strain
• How well the vaccine matches the circulating strains

'It's been predominantly by far an H3N2 season, which is always bad news.'-Dr. Michael Gardam, Humber River Hospital

Canadian public health officials now have preliminary data on flu vaccine effectiveness, which suggests it is about 55 per cent effective against influenza B. 

For influenza A, it's trickier to get an effective match in the vaccine. Influenza A strains, such as H3N2, tend to evolve faster than others, McGeer said. One early estimate of effectiveness for this year's influenza A vaccine pegs it at about 10 to 20 per cent, depending on age.

So far across the country, the majority of lab confirmed cases, hospitalizations and deaths have been among adults aged 65 and older.

Of the influenza A strains, H3N2 has been a major player, Gardam said. 

"It's been predominantly by far an H3N2 season, which is always bad news," he said.

There's more bad news on flu in the U.S. 

"This flu season continues to be extremely challenging and intense, with very high levels of office visits for flu and hospitalization rates, all indications that flu activity is high and likely to continue for several more weeks," Anne Schuchat, acting director of CDC, told reporters on Thursday.

The flu vaccine can lessen the effects of flu infection, such as the difference between a mild illness and a hospital stay, Schuchat said, particularly for people at higher risk such as children and the elderly.