Ottawa Public Health says with flu season just underway it is still not too late to get a flu shot.

Public health officials say flu season has arrived in Ottawa with 20 confirmed cases so far, including two cases of H1N1 infections.

Last year's flu outbreak was one of the worst in years, with 69 cases at this time a year ago.

Dr Carolyn Pim, Ottawa's associate medical officer of health, said this year is shaping up to be "on par" with most previous years.

While most cases seen so far are classic H3N2 flu, the H1N1 outbreak of a few years ago — the so-called "swine flu" scare — isn't yet completely done.

There have already been two H1N1 infections in Ottawa.

H1N1 is echo of 2009 outbreak

Like many pandemics, H1N1 has an echo in subsequent years, weaker than the original outbreak, slowly fading away, said Pim.

Many Canadians were vaccinated against that strain during the pandemic, but Pim said they are no longer protected.

"The flu vaccines that we have right now generally last less than a year, that's why even if the circulating virus doesn't change, we need to get immunized every year," she said.

The H1N1 that's been isolated so far is believed to be a good match with the H1N1 in the flu vaccine, she said.

Ottawa Public Health is emphasizing that with flu season just starting, it's not too late to get vaccinated.

While regular flu clinics ended Nov. 28, Ottawa Public Health is still offering flu immunization clinics by appointment for children under five and their siblings and parents.