There was a large increase in cases of whooping cough nationwide in 2012.
In its latest report on whooping cough, the Institute of Environmental Science and Research said on Tuesday that notifications increased by 197% last year compared with 2011.
ESR said there were 5938 notifications of whooping cough (pertussis) in 2012, an increase of 197% on the 1996 cases the previous year.
From early December to early January there were 520 new cases notified, 254 of which were confirmed.
ESR said notifications remain above levels in the past two years and have been increasing consistently since August 2011.
The worst regions in the most recent period are Canterbury, Waikato, Hutt Valley and Wellington. ESR said 309 patients were admitted to hospitals and there were two deaths, a child and a baby.
The Ministry of Health said it hoped the current outbreak of whooping cough would begin to tail off over the coming year.
Deputy director of public health Fran McGrath said its priority is ensuring that young babies are vaccinated on time - at six weeks, three months and five months old.
Immunisations are then given at ages four and 11.
In Canterbury, health authorities say free vaccinations of pregnant women are helping protect young babies from whooping cough.
Since January this year, the Government's drug-buying agency Pharmac has offered free vaccinations for women between weeks 28 and 38 of pregnancy.
However, Canterbury's Medical Officer of Health Raymon Pink says such vaccinations have been available in the region since April 2012 and appears to be helping.