Australians are again being urged to protect themselves ahead of this year's flu season.

The Brisbane virus is one of four strains included in this year's vaccine.

Australian Medical Association president Michael Gannon said because influenza was constantly mutating, vaccine manufacturers often looked at what strains had affected countries on the other side of the world during its winter.

The World Health Organisation recommended the Brisbane virus be included in this year's vaccine.

It is not a new strain and also formed part of the 2016 and 2017 vaccines.

Dr Gannon said the 2018 vaccine protected against the Brisbane virus, as well as two A strains and another B-strain.

"It's so important that we reassure people about the safety of being vaccinated," he told AAP on Wednesday.

"Over the past four years we've seen an increase in the number of flu notifications in Australia and that's of concern."

Dr Gannon said part of the reason for the higher numbers of people being diagnosed was because of Australia's ageing population.

"There are a higher proportion of people in the community vulnerable to getting sick," he said.

"But the truth is we're always worried about influenza."

The flu vaccine takes up to 14 days to be effective, so people are being urged to get immunised before the season begins in May.