Five people in the Bay of Plenty have been hospitalised with whooping cough this year amid a national epidemic.
This compares with 12 hospitalisations recorded for the whole of 2017, six of which were in Western Bay.
Toi Te Ora Public Health has also been notified of 98 Bay of Plenty cases of whooping cough in 2018. There were a total of 129 cases notified in 2017.
"We do have an epidemic and I think that's the first and most important thing – that everyone is aware," Bay of Plenty Medical Officer of Health Dr Neil de Wet said.
He said there were measures people could take to look after themselves and their families and the most important thing was to protect babies and children under 1 year old.
"The younger they are, the greater risk they are of serious illness."
Dr de Wet said a whooping cough epidemic of this scale often occurred every four to five years and one of the reasons was immunity wears off over time.
He said women should get immunised in pregnancy, which was a fairly new option.
Whooping cough immunisation is free for every woman between 28-38 weeks of pregnancy.
That immunisation was needed in every pregnancy, even if the woman had been immunised before.
"When you're immunised, your body responds with antibodies and those antibodies are passed over and the baby receives some immunity," Dr de Wet said.
The immunity passed from the mother lasted a few months when the baby was most vulnerable, and it was important protection before the baby could have its own immunisation.
After that, on-time and booster immunisation for babies, children and adults was the best way to protect against the disease.
Whooping cough (also called pertussis) is a serious disease and can be fatal in young babies, but that is rare.
Dr de Wet said it was also important for adults with a consistent cough to be seen, diagnosed and treated by a GP, because adults could easily pass on whooping cough to young babies.
Adults with a consistent cough should also avoid being near babies, he said.
Nationally, there were 2140 cases of whooping cough notified in 2017 and 876 so far this year.
Since November 2017, across the Bay of Plenty and Lakes districts, there have been 231 notified cases.
Dr Symon Roberton, director of Papamoa Pines Medical Centre, said he was seeing increasing numbers of whooping cough cases at his centre during this significant outbreak.
There had been about 40 confirmed cases at Papamoa Pines since December 1 last year, the GP said, and probably another 40-50 who were diagnosed clinically but did not require further investigation as they presented well after treatment times or during their infectious periods.
"This is one of the problems with the disease in that the early symptoms are much like a cold or viral illness and why prevention via immunisation is so important. Treatment does not help symptoms but limits the infectious period."
He said boosters were important because he had seen cases of the disease in unimmunised people, and in those who had not kept immunisation up to date.
"It is highly contagious, and we often see whole families affected – we have seen at least two families of five and two families of four all affected."
Dr Roberton said it was important to immunise any person who may come into close contact with a baby in the first six weeks of life.
He said although babies under 1 year old were most at risk of complications, his centre often saw elderly patients develop significant complications from whooping cough as well.
These included fainting or blacking out and apnoea (stopping breathing).