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Whooping cough on the rise – Expert Reaction

There have been 155 cases of whooping cough so far in 2024, compared with 141 cases in all of 2023.

Whooping cough, also known as pertussis, is a highly contagious respiratory disease which is particularly dangerous for babies. The Institute of Environmental Science and Resarch (ESR) reported 71 cases in May, the highest number in over four years.

The SMC asked experts to comment. 

Dr Nikki Turner, Medical Director, Immunisation Advisory Centre (IMAC), comments:

“Pertussis (whooping cough) rates are on the rise in New Zealand.

“Pertussis is always present in our communities, but every 3-5 years we get a significant rise in cases leading to an outbreak that lasts around 18 months to two years before rates return to a baseline level.

“The last outbreak in New Zealand peaked in 2017/2018, however the COVID-19 pandemic has disrupted the standard pattern of many infectious diseases, including pertussis, so we have been expecting a further outbreak for some time.

“We are now seeing a rise in pertussis cases across many regions in New Zealand, which is almost certainly the beginning of an outbreak. To date, we have had 155 reported cases this year, compared with 141 for all of last year.

“Pertussis affects all age groups with a prolonged paroxysmal cough. However, it is most severe in young infants, with around half of infants who catch the disease before the age of 12 months requiring hospitalisation, and 1 or 2 in 100 of those hospitalised die from pertussis infection. It is heartbreaking to report that there were three young infants who died from pertussis in New Zealand in 2023.

“We can prevent infant deaths and reduce hospitalisation. The NZ strategy is focused on protecting young infants firstly via pregnancy vaccination, and secondly via infant vaccination.

“Firstly, all pregnant women need access to pertussis-containing vaccines to give protection to their newborn before the infant is old enough to be fully vaccinated. Vaccination in pregnancy is over 90% effective against pertussis for infants up to 3 months of age. This is the vital first step and many in our communities are unaware of the importance of this vaccination.

“Secondly, all infants need to start their vaccination on time at six weeks of age. There are currently multiple barriers to obtaining vaccination at six weeks of age, including difficulties with all newborns being enrolled in primary healthcare, but there is an urgency to overcome these barriers.”

No conflicts of interest.

Professor Michael Baker, Department of Public Health, University of Otago, Wellington, comments:

“New Zealand’s low immunisation rates leave us vulnerable to a national epidemic of whooping cough (pertussis).

“This infection is always circulating in New Zealand and causes national epidemics when the number of vulnerable (non-immune) people reaches a sufficiently large number. The last epidemics were in 2012 and 2018. Cases dropped to low levels during the first two years of the Covid-19 pandemic but are now tracking upwards. In May 2024 we had 71 notified cases reported by ESR, the highest number for more than four years suggesting that a national epidemic is likely in the medium term.

“This situation is a further reminder about the critical need to raise immunisation levels across Aotearoa New Zealand. Pertussis is particularly serious in infants (under one-year olds) where half of those notified get hospitalised. That’s why babies should get their vaccine doses on-time at 6 weeks, 3 months and 5 months and pregnant mothers should also get vaccinated to protect their newborn babies. Booster doses are also important for children aged 4 and 11 years.

“Pertussis is also an increasing problem for older adults as immunity declines with age. About half of the notified cases are now aged 30 years and over. Vaccination is offered free to all adults at 45 and 65 years of age. It is particularly important for those with chronic lung and heart disease and a weakened immune system.

“Pertussis is highly infectious, with the typical case infecting 12 others in populations with low immunity. Cases are most infectious in the first two weeks of illness. It is very easily spread in the air when an infected person sneezes or coughs. So it is important that cases are diagnosed rapidly and isolated at home while they are infectious. Pertussis infection starts like a common cold with a runny nose, sneezing, slight fever and a mild irritating cough. After a week or two, coughing fits (paroxysms) are the main symptom and can continue for several weeks.”

No conflicts of interest.

Professor Peter McIntyre, Department of Women’s and Children’s Health, Dunedin School of Medicine, University of Otago

“The ESR pertussis dashboard shows a substantial spike in reported pertussis cases in May 2024 (74, increasing from 22 in April) which is the highest number in any single month since August 2023 (34) and just prior to COVID lockdown in February 2020 when 54 cases were reported.

“Notably, in 2023 I and co-authors reported an alarming cluster of 3 pertussis deaths in very young infants in February and March.  Similar numbers caused significant alarm in England earlier this year, despite England having more than 10x the population of New Zealand. Fortunately, no further pertussis deaths occurred in New Zealand last year, but 20 hospitalisations in infants less than 6 months were reported across the whole of 2023.

“The most important data to look at in 2024 is infant hospitalisations because it is in this age group that the most severe disease occurs – 9 to the end of May and another 5 in children less than 5 years. So broadly in keeping with what was seen in 2023.

“What does this mean? Countries NZ compares itself with (Australia, UK and Europe) are also reporting pertussis surges and there is good evidence that, as was the case for RSV and Flu, this is driven by “immunity gaps” – many people are not aware that Flu, RSV, pertussis and other respiratory infections (including COVID) cause many many more infections with no or minimal symptoms than with symptoms, especially severe symptoms and that these asymptomatic infections make an important contribution (along with vaccination in the case of pertussis and flu) to the level of immunity in the community.

“What can we do about it? We have fantastic tools to protect our youngest infants – the best is mothers being immunised against pertussis and flu in pregnancy and the good news is that this can be done in pharmacies and hospitals and some midwifery services as well as by GPs. Next best is timely vaccination of babies at 6 weeks, 3 months and 5 months – even one dose for an infant provides substantial protection against hospitalisation or death but three is obviously best.

“Unfortunately pertussis is back – we need to make sure our immunity is good as it can be and we have the tools to do that but we need parents and expecting parents to be fully aware how nasty pertussis can be and that vaccination is our only protection – one you have pertussis symptoms, there is no useful treatment available.”

No conflicts of interest.

Dr Julianna Lees,  Public Health Physician, Health Intelligence and Surveillance, Institute of Environmental Science and Resarch (ESR), comments: 

“Pertussis case numbers for the year to date (155 cases), are substantially higher than for the same time period in 2020, 2021 and 2022, when there was very little pertussis activity in the community. However, the national pertussis case numbers in 2024 to date are substantially lower than case numbers seen in 2015 and 2016 (358 cases and 452 cases, respectively).

“This year, national pertussis cases were higher in May (73 cases) compared with April (22 cases). However, the number of weekly cases has decreased over the last four weeks. There have been 11 new pertussis cases reported in the week ending 7 June, compared with 22 cases in the week ending 10 May.

“Cases have been reported across all four Health New Zealand regions. In the four weeks to 7 June, the Central region had the highest number of notified cases (30 cases), followed by Northern (14 cases), Te Manawa Taki (8 cases) and Te Waipounamu (7 cases).

“The most recent New Zealand pertussis epidemic was in 2018, and pertussis epidemics typically occur every three to five years. Due to the absence of community circulation of pertussis during the COVID-19 response, it is unclear what will happen to pertussis case numbers across New Zealand over the rest of the winter, and when the next epidemic will occur.

“We recommend a pertussis vaccine for all eligible people who are not yet up to date with their immunisations. This includes pregnant people, all children under 18 years old and adults from 45 and 65 years old.”

No conflicts of interest declared.