The Ministry of Health says there's been a significant increase in whooping cough cases but it's too soon to say if it will become an epidemic.
The Institute of Environmental Science and Research says there have been 147 whooping cough notifications this month.
Forty-four of these were in Nelson/Marlborough, 35 from West Coast and 34 from Canterbury.
Another 25 cases were notified in Wellington and the Hutt Valley, along with 9 from Hawke's Bay.
The disease is particularly prevalent on the West Coast, where there have been 110 cases reported since May.
Nelson medical officer of health Jill Sherwood says the number of cases is such that there could be a national epidemic similar to one between 2004 and 2005.
However, the Ministry of Health says it's too early to say whether that will happen but there has been an increase in whooping cough in the past couple of months.
It says more effort must go into getting babies vaccinated on time.
Vaccination is free at six weeks, three months and five months, with boosters at four and eleven years of age.
The vaccine remains potent for about ten years.
