Influenza rates rose by 21 per cent in Hunter New England in a week, as NSW Health warned that children under five were at highest risk from the deadly virus.
The latest NSW Health Respiratory Surveillance Report, released on Thursday, said there was "likely to be continued influenza activity for the next few weeks".
However, there was "some indication of a plateau in emergency data and notifications" for the flu.
NSW Health urged families to "stay up to date with their vaccinations during the school holidays to prevent serious respiratory illness".
Hunter New England recorded 1622 flu notifications in the week ending July 6, rising from 1343 the week prior.
These figures account for people unwell enough to take a PCR test.
NSW Health executive Jeremy McAnulty said influenza was "at high levels across all age groups in the community, with the highest rates in children under 16".
"Children under five are at higher risk of severe illness from influenza, and the flu vaccine is available and free for children aged six months to under five," Dr McAnulty said.
"It takes 10 to 14 days for immunity to kick in after receiving the flu vaccination, so now is the time to get vaccinated to ensure you are protected when school returns."
In Hunter New England, PCR-positive COVID cases fell from 459 to 336 in a week for those unwell enough to get tested.
University of Newcastle Professor Nathan Bartlett said the winter flu season had been "relentless".
"Everyone has been sick, one after the other in families," said Professor Bartlett, of Hunter Medical Research Institute.
"You can get one infection and go straight to another. Unfortunately in many cases one infection will make you more susceptible to a subsequent infection."
He said numerous respiratory viruses and bacteria "that we weren't exposed to during COVID have made a comeback and returned more or less simultaneously."
He hoped this would only last for "a couple of bad seasons and then community immunity will start to recover".
"Then we should start to get back into a more normal cycle of infection, but it'll take a while for that equilibrium to be restored."
He said better vaccines and therapies were needed to boost immunity in the upper respiratory tract [nose and throat] to reduce infection and transmission.
Professor Bartlett said existing COVID vaccines were "stopping people from getting super-sick or going to hospital or dying, which is obviously important".
"But the virus still transmits, so it gets to evolve and figure out ways to get around our immunity."
He said better antivirals were also needed, as many people experienced a rebound effect once they stopped using them.
"We need something to give a level of general protection that helps your natural response work more effectively by training the immune system to do a bit better."
Professor Bartlett, named Newcastle's 2024 Citizen of the Year in January, is working on "a number of treatments" that would prevent COVID and other bugs.
This was particularly aimed at vulnerable people, so they could take a nasal spray or better antiviral to prevent viruses taking hold.
