An outbreak of whooping cough that struck nearly 6000 people last year - including two children who died - shows no signs of abating.
The highly infectious bacterial infection, also known as pertussis, causes severe coughing. It can lead to pneumonia, brain damage, convulsions and death in infants.
The latest outbreak began in August 2011.
Symptoms can last three months. It is sometimes referred to as the 100-day cough.
Seven per cent of the 5938 notified cases between last January and December were in babies aged under one year, the latest Environmental Science & Research report says.
Six-week-old Alaya-Reign Pamata Ma'anaima died in Christchurch Hospital in November, nine days after being diagnosed with whooping cough. A 3-year-old unimmunised child with underlying health conditions also died.
A further 307 people were admitted to hospital. Nearly 60 per cent of these were babies aged less than one year, including 38 aged under six weeks.
Newborn babies are particularly susceptible because they cannot be fully immunised in their first six months, Immunisation Advisory Centre director Nikki Turner says. This is why it is important for parents and adults who come into contact with newborns to ensure they are immunised.
"We get it through the whole community, but the little kids suffer the most."
Outbreaks usually lasted about 18 months and a handful of deaths were expected, Dr Turner said.
"It has come when we expected it to and it's still in the peak of it. We would hope to start seeing it wane soon."
From January 1, the Health Ministry made vaccines free to women between 28 and 38 weeks into their pregnancy.
Those who had the vaccination in childhood or more than five years earlier should have a booster between 31 and 33 weeks.
Waikato was the first of several district health boards to start offering free booster vaccines to expectant mothers towards the end of last year.
Wellington mum Anna Gibson discussed her daughter's experience with whooping cough in Ministry of Health material on the infection, saying that if she and her partner had known the dangers of whooping cough, they would have boosted their immunity before the birth of daughter Mackenzie.
She was admitted to hospital for 10 days when she was seven weeks old after catching the disease from her dad.
"It was truly awful seeing Mackenzie so ill," Miss Gibson said. "She would cough and cough and cough until she was blue and not breathing. We felt so helpless as there wasn't much we or the hospital staff could do but wait and comfort her."
It is an experience they do not want other parents to go through.
"We could possibly have prevented it if we had both arranged for a booster shot when she was first born."
In the last four weeks of 2012, the highest number of cases, excluding cases under investigation, were reported in Canterbury (66 cases), Waikato (51 cases), Hutt Valley (41 cases), and Capital & Coast (37 cases).
Outbreaks occur every three to five years. During the last epidemic in 2004-05, more than 5000 cases were reported.
One child died and 159 children were treated in hospital.
The best way to protect your baby from whooping cough is to take them for their free immunisations at six weeks, three months and five months. Booster doses are given to children when they are 4 and 11 years old.
The disease is most infectious in the first couple of weeks, when symptoms are like a normal cold. It continues to be infectious three to four weeks after the cough starts.
Many babies catch whooping cough from their older siblings or parents - often before they're old enough to be vaccinated.
It is important to stay away from others if you have whooping cough.
Doctors can prescribe antibiotics, which will reduce how long you are infectious for, but unless they are given early they may not relieve your symptoms.
Source: Health Ministry
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