More than 370 cases of whooping cough were recorded in Hunter New England in August, the highest monthly amount in 30 years.
And in September to date, 90 cases had been recorded.
The cases refer to those who were unwell enough to take a PCR test for whooping cough, also known as pertussis.
NSW Health warned on Thursday that "whooping cough infections continue to rise across the state".
It urged pregnant women, parents and carers of babies, grandparents and others in close contact to be vaccinated.
It said this would "protect babies from severe disease".
The latest NSW Health Respiratory Surveillance Report, released on Thursday, said more than 12,000 cases of the disease had been reported in the state this year.
Outbreaks of pertussis usually occur every few years as population immunity wanes, with babies and young children at highest risk.
From 2020 to 2023, there was only a small number of recorded cases due to lockdowns and social distancing stopping the spread of bugs.
NSW Health director of communicable diseases Christine Selvey said vaccination in pregnancy was "very important to help protect newborn babies".
"Free whooping cough vaccines are available for all pregnant women," Dr Selvey said.
"Pregnant women are recommended to be vaccinated between 20 and 32 weeks of every pregnancy.
"This enables whooping cough antibodies to be transferred to their unborn baby."
She said parents and carers should "ensure all children are vaccinated on time, especially in the first six months of life".
Vaccination for the disease occurs at 2 months, 4 months, 6 months, 18 months and 4 years under the national immunisation program.
"It's also important all people in contact with newborn babies have had a pertussis vaccine within the previous 10 years," Dr Selvey said.
"People aged five and over can receive pertussis vaccination from GPs, pharmacist immunisers and Aboriginal medical services."
Recorded cases of the disease - known as the 100-day cough - were "increasing in all age groups", but were highest in schoolchildren.
The disease is caused by the bacteria bordetella pertussis.
Signs and symptoms:
- Whooping cough starts like a cold with a blocked or runny nose, sneezing, mild fever and occasional cough.
- Coughing bouts can worsen and be followed by vomiting, choking or taking a big gasping breath, which causes a whooping sound. The cough can last for weeks and be worse at night.
- Some newborns may not cough at all, but stop breathing completely and turn blue. Other babies have difficulties feeding or they can choke and gag.
- Older children and adults may have a mild cough that doesn't go away. In adults, the cough commonly lasts five to seven weeks, sometimes longer.
- People with symptoms should contact their GP early.
- After five days of treatment with antibiotics, people with whooping cough are no longer infectious but without proper treatment they will remain infectious for 21 days.
- If given early, antibiotics can reduce the duration of symptoms. Antibiotics are rarely needed if it has been three weeks since cough onset.
- Call Healthdirect on 1800 022 222 if unsure where to get treatment.
