Had your flu shot yet? If you're still procrastinating, here's some news to get you off the fence.
As we move into the peak of flu season, we're hearing of a return visit to Canada of a most unwelcome visitor – the H1N1 influenza virus.
The H1N1 flu strain, which sometimes is called swine flu, was responsible for between 151,000 and 575,000 deaths worldwide in the 2009-2010 pandemic, including 428 in Canada, where some 33,500 people were sickened by it, according to the Community and Hospital Infection Control Association of Canada.
H1N1 never really left, but health officials say it's coming back strong this year.
According to the Public Health Agency of Canada's FluWatch site, the H1N1 sub-type of Influenza A virus has been responsible for the vast majority of of reported cases this season, accounting for most of the flu-related hospitalizations.
[ Related: H1N1 virus returns, triggering flu vaccine warning ]
FluWatch's weekly report for the first week of December shows a spike in cases, with sporadic activity in much of Western Canada, Ontario and western Quebec.
The H1N1 strain is responsible for eight of the 12 Influenza A cases reported to the Middlesex-London Health Unit in southern Ontario, CTV News reported. Eleven victims had not received a flu shot.
It's also resurfaced in Alberta among the 97 laboratory-confirmed flu cases so far this season, the Medicine Hat News reported.
“The predominant strain is influenza A and in the last three weeks we are seeing H1N1, which was the pandemic strain,” Dr. Vivien Suttorp, medical officer of health for Alberta Health Services South Zone, told the News.
This year's flu vaccine includes protection against H1N1, Dr. Danuta Skowronski, the B.C. Centre for Disease Control's lead expert for influenza, told CBC News. But its effectiveness likely will be similar to last year's vaccine – about 60 per cent, she said.
Canadians who were around in 2009 also will have acquired some immunity through exposure to the virus, but those born since the pandemic will be more vulnerable, especially since H1N1 seems to hit young people harder.
"The H1N1 virus will appear to most people like the regular flu," Skowronski said. "Most people will recover. But hospitalizations and death are possible and with H1N1 that's most likely for young people with chronic conditions."
The flu kills anywhere from 2,000 to 8,000 Canadians a year, usually hitting the elderly and those with weak immune systems the hardest.
"Flu seasons are very unpredictable and they need to be looked at on a case by case basis," Tristan Squire-Smith of Middlesex-London Health Unit told CTV News. "It's hard to predict what's going to happen one year to the next ... We aren't more concerned this year than we would be any other."
Health officials are urging people who haven't yet been vaccinated to get their shots now. It takes about two weeks for the vaccine's immunity to kick in.
The predominant strain is influenza A and in the last three weeks we are seeing H1N1, which was the pandemic strain.— Dr. Vivien Suttorp
“No vaccine is 100 per cent but it confers a level of immunity,” said Suttorp.
The Alberta health officer added that even after someone is over the flu, people can be susceptible to secondary bacterial infection.
“This can happen as a result of an altered defence mechanism and could lead to pneumonia," she told the News. "We recommend all those over the age of 65 be vaccinated for pneumonia.”
The 2009-10 outbreak apparently has also produced a bizarre after-effect – narcolepsy.
CTV News reported scientists have found a correlation between H1N1 and a worldwide outbreak of instant sleep in 2010.
The illness was characterized by sudden, uncontrollable sleepiness and muscle weakness, which researchers said was due to the body's immune system mistakenly destroying brain cells that make the "wakefulness" protein called hypocretin, CTV News said.
A study published this week found the immune cells that tried to kill the H1N1 virus also attacked the hypocretin in patients genetically predisopsed to narcolepsy.
The discovery has helped pinpoint the cause of narcolepsy as an auto-immune disease by pinpointing the cells being attacked, which will lead to better ways of diagnosing and treating the disease, scientists told CTV News.