Flu cases in Australia have dropped by a dramatic 83 per cent in what doctors say is the result of science, guesswork and "a bit of luck".

Key points: Federal Government figures show sharp drop in flu cases since January compared to 2017

Federal Government figures show sharp drop in flu cases since January compared to 2017 Fall largely due to more accurate vaccinations, doctors say

Fall largely due to more accurate vaccinations, doctors say Decrease may not continue next year as scientific guesswork changes rapidly

There were just 40,000 flu cases recorded from January to September, compared to almost 230,000 cases in the same period last year — according to Federal Government figures.

The Australian Medical Association's ACT president, Antonio Di Dio, said the decrease was due to more people getting immunised, and a more effective vaccine being used this year.

"Every year the health authorities choose to keep some of the strains from the previous year and add one or two new strains to substitute for a new strain — and it's basically a very intelligent, well-researched guess — but ultimately a guess," he said.

"Last year was the first year for a long time that the flu injection was not nearly as effective as it usually was because the most virulent strains we had in Australia were not completely covered by the vaccination. This year they got it right."

Because flu viruses are constantly changing, the vaccine is reviewed each year and updated to include the influenza viruses that made people sick in the previous season, Dr Dio explained.

It is a worldwide effort, with more than 100 national influenza centres around the globe conducting year-long flu surveillance, before sending representatives to the World Health Organization's bi-annual influenza meetings.

Those meetings, which include representatives from Australia, are used to decide which virus strains to include in the influenza for both the Northern and Southern Hemispheres.

Flu virus is tiny but complex

The ACT's Chief Health Officer, Professor Paul Kelly, said the process was complex.

"It's a bit of science and a bit of luck, really," he said.

"We really try to predict what's going to happen to a virus that we know changes itself quite quickly sometimes — nine months out from the next flu season."

However, despite this year's low flu numbers, Professor Kelly urged people to remain vigilant with vaccinations.

"The issue with the flu virus is it's a tiny thing, only six genes I think, but it has this ability to change itself. And even subtle changes can remove that immunity that you build from a previous infection," he said.

Despite this year's improvement, Dr Dio warned against complacency.

"Just because we didn't have flu this year — so much anyway — that doesn't in anyway predict next season," he said.

"So it's likely flu will still be a problem, as it is each winter."