The arrival of the seasonal flu vaccine has been delayed about one month in Canada. Although the timing isn't ideal, influenza experts aren't worried.

In Canada and Europe, the flu vaccines won't arrive at doctors' offices and clinics until November, about one month later than usual.

Manufacturers usually receive small amounts of the three most common flu strains recommended by the World Health Organization, and then they grow the virus in eggs, which takes about six months.

This year, one of the strains, A/Wisconsin, was difficult to grow, said Dr. Patricia Huston of the Public Health Agency of Canada.

Public health experts said it would be better if the vaccine was available by mid-October to increase the time for getting people vaccinated, but flu cases don't usually peak until around Christmas time.

"We should be able to get the vaccine into people's arms if influenza behaves the way it typically does before the peak in flu activity," said Dr. Danuta Skowronski, a physician epidemiologist with the B.C. Centre for Disease Control.

There may be a benefit to delaying the vaccine, said Dr. Chingiz Amirov of Toronto's Baycrest Geriatric Health Care System.

Some experts recommend delaying administration of the vaccine until early November so its effects last into the spring when the flu season is still active, Amirov said.

It takes about two weeks for the immune system to respond to the shot and build up immunity. People can still contract influenza if they get the vaccine, but it helps reduce the severity of symptoms.