Whooping cough: “We are in a cyclical epidemic, a gentle and moderate recovery which does not cause concern”

Fatima Aït El Belghiti is an epidemiologist in the vaccine-preventable infectious diseases unit, particularly in charge of whooping cough, at Public Health France.

Why are we seeing an increase in the number of whooping cough cases?

There is an increase in whooping cough in Europe, which may or may not be worrying. This is not the case for France. There are several explanations.

First, whooping cough, which is not a seasonal disease, is a cyclical disease. Every three to five years, there are peaks, it’s normal, we don’t worry, it’s part of the illness. In twenty years, we have observed 6 to 7 peaks since the start of surveillance of the pathology started in 1996 by the Reancoq network. They are of different magnitude, we can have peaks at 160 cases, and others at 500 cases. The last peak we had in France dates from 2017-2018. We expected to see a new peak in 2021-2022, it did not happen: confinements and the implementation of barrier measures with Covid meant that whooping cough, an extremely contagious disease (one case causes between 15 and 17 sick), has completely disappeared from the radar. We had never had so few cases of whooping cough in twenty years of surveillance.

We arrived today with an immune debt, due to lack of exposure to diseases, our antibodies were not able to renew themselves, there was no “update” of our immune system. As a result, upon contact with the bacteria, we develop the disease more easily.

The only question we can’t answer is how big the peak will be.

Where are we in the epidemic?

In Europe, the situation began to simmer at the end of 2023. In France, it began in January 2024, with the first cluster cases reported to Public Health France in 2 to 3 regions. So far, eight regions were affected, a ninth has just been reported to me. We don’t know how far it will go.

Nine regions including Occitanie?

Yes.

“We are not in a situation that gives rise to concern”

For how many cases in total?

We are being informed of grouped cases, that is to say clusters, knowing that we are talking about “grouped cases” based on two cases.

At Public Health France, we are interested in community clusters. The increases we have had since the start of the year have challenged us due to their greater frequency than usual and the number of regions affected in just one quarter.

In 2023, we have only had two clusters, in Ile de France, reported in the last quarter of the year (October/December), with around 18 cases. Today, since January, we have more than 20 clusters. We stopped counting cases, but I can tell you that when we identified our first ten clusters, we counted around 70 cases, knowing that it is never possible to count them all (whooping cough is not a notifiable disease). What interests us is to see where they are located, that is to say which communities they concern and whether populations at risk of serious forms can be affected.

Should we be worried?

It’s not a serious factor, and that’s not surprising.

Will the whole of France be affected in the short term?

Yes. But we are not in a situation that gives rise to concern. We are in a moderate recovery of the epidemic, gentle and progressive. This is a sign that vaccination coverage in France is good, and that we have the positive effects of the 2018 vaccination obligation.

But when I inquire about the cases reported to me in family clusters, it often appears that the children or parents are not up to date with their vaccinations. Normally, the vaccination schedule is a first dose at the age of two months, then at 4 months, and a booster at 11 months. Then a reminder at 6 years old. In primary school, we were sometimes informed of between five and six cases in the same kindergarten class, in children who are five years old.

Why is the vaccine not working well?

It is effective, it does not prevent the disease, it reduces the risk of serious forms, hospitalization and complications. The duration of protection is estimated between 5 years and 10 years when you are vaccinated, it depends on each person’s immune system. If you catch the disease, it can last up to 15 years.

But the vaccine used has changed. It no longer contains pertussis bacillus, it is acellular, that is to say made from immunizing antigens. Whole-cell vaccines were very effective but had side effects. The acellular vaccine was introduced in France in 1998 for boosters and then replaced whole pertussis vaccines for all vaccinations in 2006.

“The vaccination schedule has already been adapted in 2013”

And this vaccine is less effective?

It is just as effective but the duration of protection is shorter.

Shouldn’t reminders be given earlier?

The vaccination schedule was already adapted in 2013.

What are the consequences of whooping cough, do we still die from it?

In the 1950s, whooping cough was a hospital burden… the WHO estimated that in 1950, for a world population of 2.5 billion, 4 million children under the age of five died from whooping cough compared to 60 000 to 100,000 in 2020. The first vaccines against whooping cough were developed in 1940 in the United States, in France the first vaccine was introduced in 1959. And in 1966, vaccination against whooping cough was generalized by combining it to the trivalent diphtheria tetanus polio vaccine.

We monitor deaths among children under 12 months of age, those most at risk. 90% of deaths reported to us affect children under two months old, who have never been vaccinated. It’s rare. Between 2016 and 2019, there were 4 deaths among children under ten days old.

“The common cough becomes a hacking cough, it’s exhausting”

But apart from the very young, very exposed, what are the after-effects of whooping cough?

You can be sick for eight weeks, with sudden coughing fits, which are poorly tolerated in children under three months because they will have difficulty catching their breath. In extreme cases, sudden deaths in unvaccinated infants can occur.

In children, also unvaccinated, the common cough will become severe, it is violent, exhausting, with risks of secondary pulmonary infection, vomiting, etc.

The forms will be lighter in vaccinated children or adults, but always with fatigue.

In adults, we are very vigilant about pregnant women, people with asthma, and immunocompromised people. I remind you that vaccination has been recommended for pregnant women since April 2022.

Are antibiotics effective?

The antibiotic treatment will not influence the progression of the disease but will allow the patient to return to the community. We will no longer be contagious after three or five days of treatment, depending on the macrolide used.