What you need to know about the whooping cough epidemic

• Health officials declared a pertussis (whooping cough) epidemic last week
• Te Whatu Ora is urging people to get vaccinated, and says babies are particularly vulnerable to the life-threatening infection
• Pertussis can be a severe disease, particularly in young babies, causing respiratory, feeding and neurological complications, and even death

New Zealand has declared a whooping cough epidemic, the fourth since it became a notifiable disease in 1996.

Caused by the bacteria Bordetella pertussis, the highly contagious illness - known as whooping cough for the whoop sounding intake of breath that can follow coughing fits, or as the 100-day cough, for the lingering cough that can take weeks or months to resolve, causes breathing difficulties and severe coughing fits.

In the four weeks before the epidemic was announced, there were 263 cases of whooping cough - the highest number of cases over a month so far in 2024, with previous spikes in May, June and July.

Immunisation Advisory Centre founder Dr Nikki Turner said the epidemic would be "long and slow", and likely to last for 12 to 18 months.

It has been a notifiable disease in New Zealand since 1996, peaking in epidemics every four to five years since.

Whooping cough is particularly dangerous for babies - especially those who have not been vaccinated. Prior to immunisation, pertussis was a major cause of infant death.

More than half of infants with pertussis are admitted to hospital, with one in six requiring admission to paediatric intensive care. One in six of those admitted to ICU will die or be left with brain or lung damage.

Of the 13 babies younger than two months old diagnosed with pertussis since the start of this year, 12 have required hospitalisation.

Antenatal immunisation from 16 weeks pregnancy has been shown to be more than 90 percent effective in preventing spread to babies.

However, overall coverage for the antenatal vaccine was 44 percent in 2018.

Immunisation stimulates the mother's immune system to make protective cells - antibodies - that circulate in the blood stream, making her less likely to get sick with whooping cough, while also crossing the placenta to her baby's blood stream, protecting them from severe whooping cough for up to three months after birth.

Te Whatu Ora says the vaccine is most effective when given from 16 to 26 weeks of pregnancy, but is available and free from 13 weeks onwards.

Once babies are born, they should have a vaccine at six weeks, three months, and five months old. Boosters are available at four and 11 years old.

A 2010 paper published in the New Zealand Medical Journal found the delay in receipt of any of the three infant doses of pertussis vaccine is associated with a five-fold increased risk of hospital admission.

In 2023, the rate of one year olds who had been vaccinated was 63 percent, this had risen to 82 percent by 2024.

Whooping cough vaccines are free for pregnant people, all children and young people under 18 years old and adults at 45 and 65 years old, as immunity reduces.

Which vaccine is used

The vaccines used to provide whooping cough protection also protect against other diseases.

• Babies are given the diphtheria, tetanus, whooping cough, polio, hep B, and haemophilus influenzae vaccine
• 4-year-olds are given the diphtheria, tetanus, whooping cough, and polio vaccine
• Those aged 11 and over are given the tetanus, diphtheria, and whooping cough vaccine (Boostrix)

It is not possible to separate these out, there is no whooping cough-only vaccine available in New Zealand.

It is recommended - though not funded - for some adults to have a whooping cough booster at least every 10 years, including:

• People that work with young children and vulnerable people
• Those that live with a newborn baby, particularly premature babies
• Anyone at higher risk of severe illness from whooping cough, like those with chronic respiratory disease

People can carry and spread whooping cough without symptoms.

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 in a period when there was no epidemic. For children, the figure was 17 percent.

If you are not eligible for a free whooping cough booster, it will cost between $40 and $90.

Symptoms (after about one week):

• Blocked or runny nose 
• Sneezing 
• Mild fever 
• Uncontrollable coughing fits that last for a few minutes 
• Coughing that leads to vomiting 
• Thick mucus that can make you vomit or choke

During coughing spells, young babies may gasp for air, stop breathing and turn blue.

Symptoms can present differently in infants, who can stop breathing or even die suddenly instead of having coughing fits.

Older children and adults can develop complications including collapsing after severe coughing, broken ribs, and pneumonia.

Patients of all ages can suffer from brain inflammation (encephalitis), convulsions and incontinence.

The coughing fits can last for a month or more, while an irritating cough can continue for longer, and can return whenever the person gets a cold or virus for the following year.

How is whooping cough treated?

There is no treatment for whooping cough. Antibiotics given early enough - before symptoms become obvious - may reduce symptoms, but once cold-like symptoms or a cough has started, antibiotics are mostly used to reduce spread.

Because babies under a year old have the highest risk of developing complications, they may need to be hospitalised for oxygen treatment, have mucous removed from their nose and throat with suction or be given fluids or liquid nutrition.

Current outbreak

The latest ESR data, which covers the four weeks up to 8 November, showed rates were highest among infants less than a year old, those most vulnerable to severe disease, and with a high proportion requiring hospitalisation.

It also identified hotspots in in Wairarapa, Southern, Whanganui and Capital and Coast health districts.

Wairarapa had 13 cases, which was by far the highest rate at 25.4 cases per 100,000 people.

That was followed by Southern at 11.6 (42 cases), Whanganui at 11.4 (8 cases) and Capital and Coast at 10.4 (34 cases).

Immunisations drop

Globally, the drop off in routine childhood immunisations during the Covid-19 pandemic was the largest sustained decline in a generation, followed by with preventable outbreaks of measles and polio.

A research paper in the Lancet medical journal suggests the deaths of three young babies with whooping cough last year were most likely caused by a combination of lowered population-wide immunity resulting from closed borders and social distancing during the pandemic, low uptake of maternal vaccinations in pregnancy, and long-standing delays for young babies getting vaccine doses, which deteriorated further during 2022.

A 2023 report on the national immunisation programme by the Immunisation Taskforce, commissioned by Te Whatu Ora, found that despite the proven lifesaving role of antenatal immunisations for pertussis and influenza, there was "no recognisable and consistent system," and "no overall governance, responsibilities or accountability" in place.

"It is essentially left to chance, with highly variable outcomes," the taskforce found, calling for a "nationwide, centrally governed system" to be urgently developed and rolled out.

Announcing the epidemic, Te Whatu Ora national clinical director for protection Dr Susan Jack said the National Public Health Service was well prepared to manage the epidemic, and a national response team had been stood up to coordinate and support activity across public health services.

However, some have raised concerns that the same day the epidemic was announced, the National Public Health Service warned staff of a "reset" before Christmas to cut millions of dollars from its budget.