There's been a spike in whooping cough cases, a potentially fatal disease for babies.

Te Whatu Ora sent a notification to GPs, hospitals and hauora Māori clinics on Thursday warning them to be on the look out for the disease - also known as pertussis - and to protect the most vulnerable.

There have been 58 cases formally notified in May, the highest since the start of 2020.

Immunisation Taskforce chairperson and Māori paediatrician Owen Sinclair says whooping cough has been at relatively low levels since the Covid-19 pandemic.

"We are really worried ... it's too early to know whether it's the start of an epidemic spike or just a return of normal spread but either way it's not good and it puts babies lives at risk."

There will be many more people in the community with the disease which could range from a cough to something much more dangerous - particularly for babies.

"They cough and then they go blue and then you put their arms about their head and sort of waft oxygen over their face and go 'please breathe, please breathe.' And they do or they don't ... there's nothing you can do about it, says Owen.

"It's awful. It's really distressing from a medical perspective. You just feel so helpless."

Te Whatu Ora's national clinical director for protection Susan Jack says New Zealand, like many countries, has outbreaks every three to five years.

New Zealand's last big one was 2017 and 2018, so it's due for another, she says.

In its notification to clinics, Te Whatu Ora told them about the increase in cases, reminding them to test people with symptoms and to vaccinate or give preventative antibiotics where needed.

Susan is worried about falling childhood immunisation rates because the disease can be so dangerous for babies.

They are not able to be vaccinated until they are six-weeks-old, so she urges those who are pregnant to get the jab.

"This is to protect their baby because newborn babies are the ones most vulnerable for whooping cough and the best protection is for their māmā to have been vaccinated," she says.

Last year, three babies died from the disease despite no apparent spike in community cases.

There have been no deaths in 2024, but 25 people have been hospitalised, six in May, she says.

Owen says any outbreak will disproportionately affect Māori and Pacific children and he wants every effort made to give them better access to vaccinations.

Susan says immunity wanes over time and free boosters are also available for those aged between 45 and 65.

The notified May cases had been in Wairarapa (12), Canterbury (10), Capital Coast and Hutt Valley (8), Counties Manukau (5), Lakes (4), Bay of Plenty (4),Tai Rāwhiti (4), Auckland (4), Waikato (3), Hawke's Bay (3) and Waitematā (1).

-RNZ.