Although the coming flu season may be far less severe than last year, doctors are urging the public to be vaccinated in case a third wave of the H1N1 virus breaks out.

Dr. Neil Rau, a microbiologist in Oakville, Ont., said he believes the flu will be kind to Canadians this winter, based on Australia's relatively mild flu during the colder months of the southern hemisphere this summer.

However, doctors are closely watching a genetic change in the H1N1 virus. That strain doesn't currently pose a threat but if it "were to drift," Rau said, "we could have a more serious year."

A slightly new form of the virus has appeared in South Pacific countries, according to a new article in the online publication Eurosurveillance.

"These variants were first detected in Singapore in early 2010 and have subsequently spread through Australia and New Zealand," the research article says.

It's too early to tell whether a new vaccine will be needed to treat the new form of H1N1, according to the article, whose lead researcher was Ian Barr of the World Health Organization.

"However, it may represent the start of more dramatic antigenic drift of the pandemic influenza A(H1N1) viruses that may require a vaccine update sooner than might have been expected," the article says.

There are also two strains of seasonal flu currently circulating in Canada. Winnipeg's medical officer of health, Dr. Carol Kurbis, said that sporadic flu cases are already being reported and that "in just a matter of time we will get more activity."

Public health nurses have begun to inoculate patients across the country, while family physicians are focusing on vaccinating children in particular, said Dr. David Greenberg.

"The kids are the ones who give it to everyone else," he said from Toronto. "They are way more exposed to it, they are sicker and contagious for longer than adults."

A new nasal spray has also been approved for use in Canada, which doctors hope may help encourage the public to get vaccinated -- whether the flu season is mild or severe.

Last year, the World Health Organization declared the new H1N1 strain a global pandemic. More than 8,000 Canadians were hospitalized and more than 400 died.

Randy Romando was one of those who came down with the H1N1 flu.

"It was 15 days before the fever broke," he said. "I've never been that sick."

With a report from CTV's medical expert Avis Favaro