With more than 100,000 cases and around thirty deaths, France is experiencing its worst whooping cough epidemic in more than a quarter of a century. Several hypotheses have been put forward to explain this resurgence.
An epidemic of whooping cough has been observed in France “since the beginning of 2024 with a very significant circulation of the bacteria which has intensified in recent months”, summarized the Public Health France agency on Wednesday.
This outbreak, also observed in many other countries, has reached an unprecedented level in France for “at least 25 years”, according to the Pasteur Institute, a French foundation at the forefront of the fight against infectious diseases.
More than 130,000 cases have been recorded since the beginning of the year, according to figures from the public health agency, which is based on consultations with private doctors. The movement accelerated throughout the spring before continuing steadily during the summer.
And, since the beginning of 2024, 35 deaths have been linked to whooping cough, including 22 children, most of them babies under one year old.
Whooping cough, marked by a very specific cough, is in fact primarily a danger for the youngest. This bacterial disease, highly contagious, is often benign, but can lead to serious respiratory and neurological complications, sometimes fatal in babies.
It is in this context that the health authorities called in the middle of summer to tighten the vaccination net. This, mandatory for the infant itself, is recommended for all close contacts with the infant, as well as for the mother during pregnancy.
Vaccination is indeed very effective and protects babies well against serious forms. But it only occurs at a few months, hence the importance of vaccinating those around little ones.
A more virulent bacteria?
But “while it is true that in France, vaccination has largely helped reduce the number of cases, whooping cough nevertheless continues to circulate cyclically, with epidemic peaks observed every three to five years between 1997 and 2019,” the Pasteur Institute recalled this week.
Then, “while we could have expected an epidemic peak in 2022 or 2023, it was delayed,” he continued.
This time, here we are, and on a special scale.
Why such a rebound? Several hypotheses have been put forward, one of which is the consequence of the Covid crisis in 2020-2021, as with other epidemic resurgences, such as measles.
The multiple health restrictions put in place at the time, including lockdowns, limited people’s exposure to multiple pathogens.
“It is possible that […] “the overall immunity of the population has been less stimulated, which is often done through asymptomatic infections,” according to the authors of a study involving the Pasteur Institute and Public Health France.
But this work, published in August in the journal Eurosurveillanceformulates another hypothesis, based on the examination of samples taken from around sixty whooping cough patients since the beginning of the year.
In these patients, the bacteria Bordetella pertussisthe cause of the disease, had a very particular profile.
In most cases, it contained two proteins that were typically absent before the COVID-19 pandemic: pertactin and the adhesin FIM2.
Now these two proteins “play an essential role in the adhesion of the bacteria to cells” allowing respiration “and in the modulation of the host response,” the institute noted. “Their current predominance, contrary to what was observed before the “COVID period”, could also explain the very strong current circulation of whooping cough,” according to these researchers.
On the other hand, another hypothesis seems less favoured: that of a decline in vaccination, against a backdrop of reduced access to the health system during periods of confinement.
“There is no evidence that vaccination against (whooping cough) has declined in France, even if delays were observed during the early stages of the pandemic,” the study noted.Eurosurveillance.