Pertussis, otherwise known as whooping cough, means little to most parents in the developed world today. But 100 years ago, it was one of the great terrors of family life.

It was so contagious that one child with pertussis was likely to infect half his classmates and all of his siblings at home. In the 1930s, 7,500 Americans died from pertussis every year — most of them infants and young children.

All of that changed because of Kendrick and Eldering. They had been hired to do routine daily testing of medical and environmental samples. 

However, research on pertussis became an obsession. With almost no funding, private donors stepped forward to fund their clinical trial of the first pertussis vaccine. Mothers volunteered not just their time but their children as participants.

Medical experts were sceptical. But where other researchers had failed, Kendrick, Eldering, and their team developed the first safe and effective whooping cough vaccine.

Through their innovations, childhood deaths from whooping cough plummeted in the US and across the world.

Almost 100 years later, whooping cough is still rearing its head in infants, causing havoc and tragic loss of life among the smallest and most vulnerable family members.

Vaccination highly effective

Vaccination of pregnant mothers with pertussis vaccine is highly effective at protecting infants under three months of age. It is also critical that infants receive their childhood vaccinations as early as possible when they are most at risk of severe disease.

Over 500 cases of whooping cough have been recorded in Ireland so far this year as of October 23. This compares to just 18 cases notified to all health authorities in all of 2023.

As whooping cough is rarely confirmed by laboratory testing in the community, this figure is likely to represent the tip of the iceberg.

Of the cases identified, as of November 1, the Health Protection Surveillance Centre (HPSC) reports that one in five (101) occurred in infants who were zero to five months old — the majority (67%) of whom were hospitalised.

These stark figures reflect the low uptake of whooping cough during pregnancy, which forms the bedrock of protection of tiny infants from severe illness and death.

Unbelievably, no data is available on the uptake level of whooping cough vaccine among pregnant women in Ireland.

A survey conducted by the HPSC in 2018 showed that less than half (48.7%) of women reported they had received pertussis vaccine during pregnancy. That was before the additional vaccine hesitancy induced by covid.

Of the infants who are diagnosed with pertussis, the majority of those under one month (84%) and three out of four of those under six months (74%) are thought to have been born to unvaccinated mothers.

Symptoms

Pertussis is a highly contagious respiratory infection that is easily spread by coughing and sneezing. Symptoms present seven to 10 days after infection but may manifest up to 21 days later.

The illness can initially resemble a common cold, with fever, sneezing and runny nose. This may progress to a persistent cough with a characteristic whooping sound that gives the disease its name.

During coughing episodes, the patient may turn blue and vomit, with several coughing episodes in quick succession causing exhaustion.

These coughing fits can be triggered by eating, laughing, or crying and are usually worse at night.

Pertussis carries the risk of permanent complications following pneumonia and seizures. Infants under six weeks are at the highest risk of death.

The critical importance of vaccination during pregnancy was outlined in a paper in the International Journal of Infectious Disease, published last June, amid a global surge in cases. Pertussis cases have increased across the northern and southern hemispheres.

The lack of immune stimulation during covid due to the reduced circulation of Bordetella pertussis, the pathogen responsible for infection, is likely to have magnified susceptibility aligned with the normal three- to five-year cyclical peaks in activity.

Resurgence after covid

In 2019, the World Health Organization reported a pre-pandemic pertussis incidence rate of 29.8 per million. These rates dropped like a stone during the pandemic to 9.2 in 2020 and 4.6 in 2021 before rising to 10 in 2022 and 22.8 in 2023.

In Europe/EEA, pertussis cases surged in 2023, with over 25,000 cases reported, and there were more than 32,000 cases between January and March 2024.

In the 11 years between 2011 and 2022, 103 deaths were reported, with two-thirds (67%) reported in infants. All but five of those deaths occurred in infants less than six months old, with most deaths occurring in one-month-olds.

From January to April 2024, there were 19 deaths from pertussis in the EU/EEA — over half (58%) of those were in infants.

According to Britain’s Health Security Agency, eight infants died after developing whooping cough during the first four months of 2024, with 4,793 new pertussis cases during that time.

In the North, there were 1,425 cases by May 26, 2024, compared with only two cases between 2021 and 2023. The Public Health Agency has urged pregnant women and parents of young children to get vaccinated to curb the outbreak.

Infants and newborns, particularly those too young to complete their primary vaccination as part of the national childhood immunisation programme, account for the majority of pertussis-related deaths in the EU/EEA.

This emphasises the importance of maternal vaccination during each pregnancy to protect newborns from severe illness and death until they can complete their primary immunisations.

The HSE recommend that the pertussis vaccine be given to pregnant women between 16 and 36 weeks of pregnancy. While the vaccine can be given later, it may be less effective. 

Ideally, it should be given at least two weeks before delivery for maximum protection. This safeguards the baby against infection for the first three months of life when they are at their most vulnerable.

Decline in maternal pertussis vaccination rates

Antenatal immunisation uptake has been suboptimal overall, particularly in the post-pandemic period. 

Several factors likely to contribute to this include a lack of awareness among parents about the risks of pertussis in newborns and the protection offered from maternal vaccination alongside increased questioning of vaccines offered in pregnancy following covid.

The effectiveness of maternal immunisation against pertussis in babies under three months is huge, estimated to be about 90% against getting the disease and 97% against death.

Mothers should receive pertussis vaccine with each pregnancy to pass on protection to their newborns during the early weeks of life.

At a time when pertussis is surging in the community, this is more important than ever to protect tiny infants from a potentially life-threatening illness that is almost entirely preventable.

Dr Catherine Conlon is a public health doctor and former director of human health and nutrition at Safefood