An Adelaide woman who spent almost two weeks in hospital battling influenza is urging South Australians not to become complacent as cases surge across the state.

Maddie Ellis, 28, was vaccinated earlier this year — but as a recovering breast cancer patient with a compromised immune system, she says the flu hit her harder than she ever expected.

WATCH ABOVE: Cancer survivor loses ability to breath as common flu hospitalises her

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She was rushed to hospital struggling to breathe and came close to being placed on a ventilator.

“It progressed very quickly and became very serious,” she told 7NEWS.

Maddie Ellis is lucky to be alive as the cancer survivor battled the common flu Credit: Supplied.

Ellis relied on high-flow oxygen. Credit: Supplied.

Ellis relied on high‑flow oxygen for days.

“We were able to slowly taper that down, but the biggest thing was that trouble in breathing,” she said.

SA Health data shows flu infections are now almost doubling each fortnight, with 325 new cases recorded last week and 11 deaths so far this year.

Health Minister Blair Boyer says there is no room for complacency.

“There’s no time for us to be complacent,” he said.

Despite repeated warnings, vaccination rates remain low — including in aged care.

Chief Public Health Officer Nicola Spurrier says a significant number of older South Australians remain unprotected.

“A third of older people, 65 and up, haven’t been vaccinated yet and that’s a group that is more vulnerable,” she said.

Flu cases have increased in South Australia as vaccination rates plummet. Credit: 7NEWS

Ellis is warning Australians to get vaccinated. Credit: 7NEWS

There has been a modest improvement among children aged six months to five years, with authorities crediting a 5 per cent rise to the needle‑free FluMist option.

“Lots of other vaccine rates have been dropping but this one’s gone up,” Spurrier said.

Ellis says protecting yourself — and others — must be a priority.

“You just never know what someone else is experiencing or how it’ll affect them,” she said.