Whooping cough vaccination rates 'dreadful' in Aotearoa, expert says

New Zealand's low vaccination rates are to blame for the danger posed by the whooping cough epidemic declared on Friday, an infectious disease expert says.

Public health authorities have announced a nationally coordinated response after 263 cases were confirmed in the last month.

Whooping cough is particularly dangerous for newborn babies, and older adults, and in some cases it can be fatal, Te Whatu Ora national clinical director for protection Dr Susan Jack said.

Auckland University vaccinologist Helen Petousis-Harris told Midday Report she was surprised it has taken so long to "get on the move" with declaring an epidemic.

"When you look at the trend it's just taken off from earlier this year and it's going into its epidemic phase by the look of it."

Most of the time the country had whooping cough cases on a regular basis but every so often there were "massive outbreaks" that occurred and they could last as long as a year.

Petousis-Harris said a booster shot for pregnant women would protect babies who would then be born with some antibodies and that had proven "really effective".

"The maternal dose is absolutely vital and as we go into the epidemic that's going to be the best way to protect the very youngest and then get those infant doses on time so they're protected for themselves."

Immunisation rates were "dreadful" at present, Petousis-Harris said.

It was also one of those vaccines that was not particularly good at preventing transmission.

"While it is pretty good at preventing someone getting sick it doesn't do a particularly good job of stopping onward transmission ...

"So that's another real challenge for us so there could be quite a lot circulating in the community. Just assume at the moment that it is probably everywhere."

The total number of cases reported by health officials would not be representative of the scale of the problem because most people would not be tested.

"Most cases may not be particularly ill so when you look at what you're seeing and you're looking at those cases being reported it's the tip of the iceberg."

Whooping cough is not a virus but "a decent-sized bacteria" that is almost as infectious as the measles virus meaning it can be easily transmitted.

"People can carry and spread it without being sick so it's another one of those that can be quietly spread within communities."

New Zealand research from several years ago revealed that of adults with a persistent cough who presented to a GP 10 percent were diagnosed as having whooping cough at a period when there was no epidemic. For children the figure was 17 percent.