The president of the Australian Medical Association ACT, Stephen Robson, said the early start to the season caught many off guard, leading to fewer people receiving influenza vaccinations.

"This catches many people by surprise and the people who hold off waiting [for vaccinations] get caught out because last year's vaccinations aren't up to date," he said.

"No doubt the flu season began a lot easier than it had in previous years, and certainly a lot more people have been affected, particularly older people in their 80s and children under 10.

"It's been quite a bad year for those groups."

As Australia is in the middle of the worst influenza outbreak in 15 years, more than half of this year's flu cases in the ACT have been reported in the past fortnight.

ACT acting chief health officer Andrew Pengilley said 988 influenza cases had been confirmed in Canberra this year.

"We've no doubt seen a rapid increase in flu cases being reported to ACT Health," Dr Pengilley said.

Figures also show more than 800 people were diagnosed with influenza in the territory since July 11.

During the past five years, flu reports have increased by 46 per cent.

Nationally, there have been twice as many cases reported between January and July 2017 compared to 2016.

There were 1603 influenza cases in 2016, the highest levels in the ACT since 2001.

Dr Pengilley said the exact flu numbers were going to be hard to predict.

"The flu season usually goes up to a peak and then goes down, usually following an epidemic curve, and we have a big curve," he said.

"Picking this peak is not an exact science, so we know there's going to be high activity and we think [high flu numbers] will continue for another few weeks. But we can't predict when the numbers will go down."

Professor Robson said while the most common strain of influenza detected this year was covered by this year's vaccination, health experts are worried that not enough people are being immunised.

"People mix up the flu, which is a serious illness, to the cold, which is potentially dangerous," he said.

"There are also huge concerns about the low levels of influenza vaccinations for pregnant women, with fewer than half getting their flu shots."

While winter is traditionally peak-flu season, Dr Pengilley said cases are still prominent as the weather warms up.

He said the best way to prevent the spread of flu is to stay away from work or large public areas at the first sign of symptoms.

"We often see people try to soldier on and then you have a whole bunch of other people getting sick," he said.

"The other important thing is washing hands because the virus can survive for a number of hours on hard surfaces and other people can pick it up."