Wanganui parents are being urged to immunise their children against whooping cough as a national outbreak sweeps the country.
Last year 149 cases of the disease - also known as pertussis - were reported in Wanganui. Another 21 cases had been reported by February this year, Institute of Environmental Science and Research (ESR) figures show.
Whanganui District Health Board's medical officer, Patrick O'Connor, said whooping cough cases had been increasing from June, dropping off only in the past two months.
"Pertussis has this habit of just coming back at you every three to five years."
When most of the population was immunised, the country should start to see a drop-off in cases, Dr O'Connor said.
This week is Immunisation Week (April 22-28), and the Government is urging parents to get their children immunised on time. At the end of the last reported quarter (October to December), 90 per cent of eight-month-old children in Wanganui had received their primary course of immunisation at six weeks, three months and five months on time.
The rate was down 0.2 per cent on the previous quarter, but 5 per cent above the national target. The vaccine wasn't perfect and cases did occur in people already immunised, Dr O'Connor said.
Recent initiatives to keep the disease at bay had included immunising Wanganui Hospital staff who work with young children, and offering free vaccinations for pregnant mothers between 28 to 38 weeks nationwide.
However, a core group of parents actively chose not to immunise their children. "That's a parental choice, in New Zealand it's not obligatory to vaccinate," Dr O'Connor said. "For some diseases it's especially important to get what's called 'herd immunity' - measles is the best example of that."
This was not so important with whooping cough as the vaccination was not life-long, he said. "In a sense, pertussis is always going to be very, very difficult to stop completely because it will always circulate among older age groups."
Associate Health Minister Jo Goodhew said the current whooping cough outbreak underlined the importance of timely immunisation. "On-time immunisation is vital to protect those most vulnerable to the disease, especially babies under the age of one."
More than 8600 cases of whooping cough have been reported since the outbreak began in August 2011 with no sign of a reduction. The highly infectious disease is caused by bacteria which damage the breathing tubes and is spread by coughing and sneezing.
Infected babies may not be able to feed or breathe properly and can suffer serious complications such as pneumonia and brain damage.
All babies and children are eligible for free immunisations against whooping cough at six weeks, three months and five months of age. Children also receive free boosters at four and 11 years of age.
Mrs Goodhew said babies needed all three immunisations for full protection as more than half of hospitalisations occurred in babies under one.