Doctors have warned the worst of the winter sickness season is yet to come and health measures are crucial.

The New England area alone has recorded about 1000 cases of COVID-19 in the past week.

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About a third are thought to be the highly infectious BA.5 Omicron subvariant, Hunter New England Health's Dr David Durrheim said.

"We believe it's now taking off in the Hunter and New England," he told ACM.

Patients with COVID in New England Hospitals have reached 13, a number that has doubled in the past fortnight as BA.5 cases increase.

Dr Durrheim said a concerning feature of the subvariant was that a previous COVID-19 infection didn't provide people much protection - meaning keeping up with vaccine boosters was essential.

"We all got very good at wearing masks and social distancing and we can still do that," he said.

"Don't spread it around."

Influenza cases have exploded in a worrying turn.

The New England area recorded zero cases across the entire season last year.

About a month ago, there were 25 cases clocked in the space of seven days.

Last week alone, lab tests confirmed 285 infections.

"That is just the tip of the iceberg ... it's an early start and it's a steep increase," Dr Durrheim said.

A PCR test can reveal a COVID-19 infection but can also confirm a flu diagnosis or another highly contagious respiratory illness known as RSV.

Dr Durrheim said hygiene and masking up work.

He urged locals to roll up their sleeves for a free flu shot and seek a PCR test if symptoms develop.

Youngsters under the age of five presenting to the region's emergency departments with respiratory problems have dramatically increased - many likely due to RSV.

"It's a horrible virus in little kids ... they really struggle to breathe," Dr Durrheim said.

He urged parents to keep unwell children at home.