A surge in the number of flu cases in Alberta, the majority of which involve the H1N1 strain, has prompted health officials in the province to open mass immunization centres over the holidays.

Between Dec. 14 and Dec. 21, the number of flu cases in the Edmonton area rose from 65 to 125, with H1N1 accounting for more than 90 per cent of the cases. The vast majority of the 250 flu cases reported in Calgary since the end of August have also been H1N1. Alberta health officials have already blamed the virus for at least two deaths.

Across Canada, seven deaths have been linked to the H1N1 virus so far. At least four of them involved adults between the ages of 45-64.

As of mid-December, hundreds of Canadians had already contracted the H1N1 flu.

Dr. Gerald Predy, senior medical officer for Alberta Health Services, says it is not unusual to see a spike in cases this time of year as people gather to spend the holidays together. However, he said that the province is still weeks away from peak season, and the recent increase in the number of cases is “just the tip of the iceberg.”

And because the outbreak features the H1N1 strain, he warns that everyone, including younger adults who often think they’re immune from the flu, should take steps to protect themselves.

“A lot of people think it’s the elderly who are at risk, but with H1N1 we just want to emphasize there is a serious risk of illness in other age groups,” he told CTV News Channel.

AHS officials, stressing it’s not too late to get the flu shot, have set up several mass immunization centres in Edmonton and Calgary that people can access over the holidays.

H1N1 first appeared in 2009 and caused widespread illness worldwide as people had no natural immunity to it. For more than a year, H1N1 was declared a pandemic influenza virus. The virus entered its post-pandemic phase in the summer of 2010, and has now become one of several seasonal flu strains in Canada.

“But again, one of the messages we’re trying to get out to people is that it’s not just pandemic strains that can cause serious illness, our seasonal influenza strains do so as well,” Predy said.

The flu has also been blamed for several hospitalizations in Saskatchewan. Officials in the province say the majority of cases are also H1N1.

Predy says there are several symptoms of the flu, including headaches, achy muscles, fever and a dry cough. But the hallmark of the virus, he says, is how quickly it strikes.

“It comes on very suddenly,” he said. “You feel fine in the morning than by noon you can’t move.”

Predy said in some cases the flu can cause serious respiratory illnesses like pneumonia. He cautioned that people should stay home from work if they have the flu. Children should also stay home from school in the new year if they’ve been infected, he added.

In the United States, health officials say they’re seeing thousands of cases of H1N1 flu. In Texas, five deaths have been blamed on the virus, but doctors say fatalities are rare.

With reports from CTV’s Jill Macyshon, CTV Calgary and CTV Edmonton