Health experts are warning Australia is on track for a killer flu season, with numbers showing three times as many people have been diagnosed with the virus so far this year, compared to the same period in previous years.

In March, more than 10,000 people were diagnosed with the flu. In March 2018, that number was 3,173.

Chair of the Immunisation Coalition, Professor Robert Booy, said those affected were mainly in New South Wales, Victoria, Queensland and South Australia.

"The data I have received shows that we are seeing three times as many cases this year as last year," he said.

At the end of the first week in April, we were nearly halfway to our 2018 annual total.

Professor Booy said so far this year, nearly 27,000 people had been struck down by flu.

New South Wales: 7,595 cases

New South Wales: 7,595 cases Queensland: 7,289 cases

Queensland: 7,289 cases Victoria: 4,627 cases

Victoria: 4,627 cases South Australia: 4,397 cases

South Australia: 4,397 cases Western Australia: 1,498 cases

Western Australia: 1,498 cases Tasmania: 322 cases

Tasmania: 322 cases Northern Territory: 296 cases

Northern Territory: 296 cases Australian Capital Territory: 203 cases

So, why is there so much flu around already?

In 2018, Australia had a pretty quiet flu season and that means that community immunity wasn't built up to protect against this year's virus.

"It means many more people will be prone to the flu this year and susceptible to getting it," Professor Booy said.

There was also a long flu season in the Northern Hemisphere earlier in the year, up until about March.

"Many Australians went to the US for holidays earlier in the year and brought the flu back, and in February, school goes back and kids mix and spread the flu," Professor Booy said.

How deadly is it?

Most deaths from the flu occur in people aged over 65, and are usually from complications such as pneumonia, heart attacks or stroke.

Professor Booy said in a busy year, there were a number of people who would be expected to get the flu and die from it.

"This year, we expect the flu to kill at least 4,000 people which is the same number as deaths from suicide and the road toll combined," he said.

Professor Booy said most years, 12 Australian children died from the flu.

"If we had a high rate of immunity in kids, it would also stop the spread of the flu to susceptible adults," he said.

Chair of the Australian Medical Association council of GPs, Dr Richard Kidd, said one in 10 people who died in intensive care from the flu were otherwise healthy.

"More than half of all kids who end up in hospital with the flu were healthy and didn't have any chronic health conditions," he said.

When to get the vaccine?

The earlier the better.

Experts said early April is a good time to get a vaccine as it takes two weeks for your immunity to develop.

"With the flu [rates] three times as high this year as last year, we can stop transmission now if people get vaccinated," Professor Booy said.

"Otherwise the numbers could rise even more."

Flu season in Australia usually runs from June to September, peaking in August.

Chief Medical Officer for the Federal Government, Professor Brendan Murphy, recommends vaccinating from mid-April in order to develop immunity before rates of influenza increase.

Where do I get the vaccine?

In most states, the vaccine has already been distributed to GPs and many pharmacies.

If you are a healthy adult with children or looking after someone with a chronic illness, Professor Booy said it was fine to go to a pharmacy for the flu vaccine.

"But if you are elderly or pregnant, it's best to go to the GP who can give you the flu shot as well as oversee your health generally," he said.

And if you are healthy, is it still worth getting the vaccine?

Experts say, yes. It's not just about you, community immunity helps protect everyone.

"I encourage healthy people to get the flu shot as it protects you from getting and from spreading it to more vulnerable groups like the elderly," Professor Booy said.

George Tambassis from the Pharmacy Guild, whose members sell the flu vaccine, said boosting community immunity was the best way to protect against the flu.

"While there are people at high risk of the flu, including those aged 65 and above, the flu can in fact strike anyone, even the young, fit and healthy," he said.

"In fact, one-in-four people who are hospitalised with the flu have no underlying medical condition."

Which vaccine am I likely to get?

This year, the four strain or quadrivalent vaccine is available for people aged under 65 years old.

People aged over 65 will get an enhanced vaccine, which has a component in it which boosts their immune system.

Separate to the Federal vaccine program, all states are providing free vaccines for babies from six months up to the age of five.

In countries such as the United States, most children get the flu vaccine for free.

Will we have vaccine shortages?

There were shortages last year, but that meant vaccine manufacturers produced a lot more doses this year.

Experts said any shortages were unlikely to happen again and if there were any supply issues, it should be fixed in a few days.

Some Australians can get a free vaccination. Who's eligible?

Many Australians can get vaccinated against the flu for free thanks to the National Immunisation Program (NIP).

This year, the Government has secured more than 6 million doses of the vaccine to help protect those most at risk of getting sick.

For the first time, all Aboriginal and Torres Strait Islander people aged six months or older will be eligible for a free flu vaccination.

Previously, only Aboriginal or Torres Strait Islander people aged six months to five years, or older than 15, were eligible.

Other Australians who are entitled to a free flu vaccination include: