Parents are being warned to protect their children against influenza as New South Wales reaches its "trigger" for an early start to the flu season.
Influenza cases have more than doubled in recent weeks and the state's Chief Health Officer, Kerry Chant, said the H1N1 and H3N2 strains were dominant.
"We've got an early indication that the flu season is starting," Dr Chant said.
"The proportion [of people who] are testing positive for flu is around 5.5 per cent and that corresponds to our trigger for calling an early start to the flu season.
"We're also seeing increased hospital presentations and hospitalisations, particularly in that 0-4-year-old age group."
There were 1,024 new cases of influenza in New South Wales in the week ending April 30, compared to just 478 cases the previous week.
Dr Chant said influenza was circulating widely in the community for the first time in two years and stressed that children under five years of age were particularly at risk.
She said vaccination offered the greatest protection against serious illness and admission to hospital, urging parents to get their children immunised against influenza.
"I know there is a lot of [vaccination] fatigue, we've asked the community to get vaccinated repeatedly," Dr Chant said.
"But it is such a critical component of protecting yourself, your loved ones and the broader society."
The influenza vaccine is free for children aged from six months to five years and is available through GP clinics.
It is also free for people considered to be at the highest risk from influenza, including pregnant women, Aboriginal and Torres Strait Islander people, people with serious health conditions and those aged over 65 years.
NSW Health said it was safe and convenient for people to get both the COVID-19 vaccine and the flu vaccine at the same time.
Health Minister Brad Hazzard admitted there was "vaccination fatigue" in the state because of the COVID-19 pandemic.
"It is crucial everyone gets vaccinated against flu to not only protect themselves, but [also] their colleagues and loved ones against serious illness or worse," Mr Hazzard said.
"Whilst we know there is vaccination fatigue, I urge the more-vulnerable members of our community to book in for a flu jab with their GP or pharmacist as soon as possible."
