A Victorian woman who recently gave birth remains in an induced coma after contracting influenza while pregnant, as an extraordinarily high number of flu cases prompts calls for stronger vaccines, and free shots for more people.

A fundraising webpage has been set up for Sarah Hawthorn, from Cobram in northern Victoria, who is in a critical condition in Melbourne's Alfred Hospital.

"During the later stages of Sarah's pregnancy she caught the flu," the fundraising page said.

"As a result her gorgeous boy arrived earlier than planned and following his birth Sarah was, and remains, in a critical condition in an induced coma."

In a statement, Ms Hawthorn's family thanked the community for their support during this time, and said her baby was doing well.

"We are grateful for the ongoing compassion and support received from our family, friends and broader community," they said.

The state's Health Minister, Jill Hennessy, said this year's flu season had been particularly tough.

"I just can't imagine what it must be like for families who, one day there's a healthy pregnant mum and the next day you've got a patient that's in a coma in a hospital," she said.

"I think that all of us feel a great degree of compassion and sympathy to her family and it is just yet another sign that it is a horror flu season.

"We're seeing some really awful and tragic consequence of this year's flu season."

Ms Hennessy said she was talking to her federal counterparts about making the flu vaccine free for more people.

Under the National Immunisation Program, those eligible for a free flu shot include people aged 65 years and over, most Aboriginal and Torres Strait Islander people and those who suffer from chronic health conditions.

"We have made a request to the Commonwealth Government that they look at the provision of free flu vaccinations, particularly for children," Ms Hennessy said.

"What we've seen with this particular strain of flu, it's not just been the elderly and the sick and the vulnerable who have been particularly susceptible, but we're seeing it in the young and the healthy.

"We would love to see free flu vaccination for everyone.

"We do understand that's an incredibly expensive exercise for the Commonwealth so if they're not in a position to do that, providing free flu vaccine for children and infants is something we're encouraging."

Bigger flu season, less severe

But Australia's Chief Medical Officer Professor Brendan Murphy said there had been a significantly higher number of cases than normal in people who have been vaccinated this year.

He said it was not clear why the current vaccination had not been as effective.

"The vaccine that was given and selected by the WHO process did contain a moderate to good coverage of the viruses, but for reasons that are still being evaluated, vaccine protection hasn't been as strong as in previous years," he said.

"So there have been a higher number of cases in people who have been vaccinated."

Ms Hennessy said this year's vaccine would need to be reviewed by health authorities.

Professor Brown said calls to provide vaccinations to children under the age of five would not be a cost issue, but more about cost effectiveness, with less than 10 per cent of children currently vaccinated against the flu.

"If you don't get a very high uptake in children you'd have to look at the benefit of that in terms of preventing transmission," he said.

Professor Murphy said the number of people who had presented with the flu was around 170,000, which made it a bigger season than usual.

But he also added that figure could be higher.

"We know that's only a fraction of the total number of people who are infected with flu, so there'll be many more than a 170,000 cases but the exact numbers we can't give," he said.

Despite those figures, Professor Murphy said the season had been of moderate severity and was not a very nasty flu season.

"There have been somewhat more admissions to hospital than usual with influenza, but they've been fewer intensive care admissions than usual so it's a moderately severe disease which has been in high numbers," Professor Brown said.

Rosie Andersen, 8, died in hospital after contracting the flu. ( Gofundme )

Push for stronger shots

Federal Health Minister Greg Hunt has asked the nation's Chief Medical Officer, Brendan Murphy, to look at ways to strengthen the program, including by speaking to manufacturers about stronger vaccines.

"This year we are providing more than 4.5 million doses of the influenza vaccine for free to Australians," a spokesman for Mr Hunt said.

"With flu vaccinations available for as low as $11, all Australians are encouraged to talk to their doctor about getting a shot each year."

Victoria, New South Wales and Queensland are experiencing their worst flu season in years.

There have been 13,000 flu cases in Victoria so far this year — nearly double the number that had been confirmed this time last year.

Eight-year-old Rosie Andersen died in a hospital in Melbourne's outer east last week after contracting the virus.

Last month, eight people died from a flu outbreak at an aged care facility at St John's Retirement Village in Victoria's north-east.