Notifications of laboratory-confirmed influenza in the ACT have reached 1238 so far this year, just 28 fewer than five years ago during the H1N1 swine flu pandemic.

A lot of the cases in the ACT this year have been H1N1 (swine flu).

Flu cases have more than doubled compared with last year when there were 568 notifications, data from the National Notifiable Diseases Surveillance System shows.

Despite the high number of notifications, 2014 has been an "intermediate" year for flu in the ACT, ACT Health acting chief health officer Dr Andrew Pengilleysays.

"It wasn't anywhere as bad as 2009 but it was certainly bigger than the last couple of years and that was replicated certainly in Australia and as far as I know, in North America as well," he said.

Dr Pengilley said flu spread in winter every year and the severity of the flu season tended to fluctuate.

"We know we can have mild seasons and we can have big seasons - 2009 was a pandemic season, the following season was not particularly big," he said.

"The thing about the flu virus is that it mutates continuously so every year there is a new strain or a slightly different variant.

"What tends to matter is how close it is to the previous year's infection so how the good the immunity people have built up from natural infections the previous year is protecting them.

"Also how good the match of the vaccine is for people who are vaccinated because the vaccine has to be based on the previous year's strains and so if there's a radical departure, the vaccine might not be as close."

Dr Pengilley said the severity of flu each year also depended on the "natural variability" of the strain of the virus.

"If you have something like an H1N1 strain, which we had quite a lot of this year, it makes people quite sick and so they know they've got flu and so they go to the doctor and they get tested," he said.

"So a combination of all those factors can make the difference."

Data for other vaccine preventable diseases reveals the ACT has recorded a steady increase in notifications of chickenpox and shingles since 2009.

There were two cases of chickenpox in 2009, rising to 38 this year so far while shingles notifications rose from seven in 2009 to 85 this year.

Cases of whooping cough in the ACT have declined since 2011 when there were 829 notifications and have reached 219 so far this year, down from 235 in 2013 and 430 in 2011.

"Whooping cough is another one that naturally cycles on three to four years, so it was big in 2009 and it's gone down again but it will come up again," Dr Pengilley said.

"Again, that's a question of waning immunity in the community."

Other data shows there have been 15 notifications of dengue virus infection in the ACT this year so far and nine notifications of malaria.