2023-04-25 05:12:36
An unprecedented increase. In recent months, France has been facing an unusual resurgence of cases of invasive meningococcal infections (IMM), alert Public health France. Meningococci, “bacteria which can cause very serious illnesses such as meningitis or septicemia, can be fatal or leave significant sequelae”, recalls the ministry of health.
But how to explain this increase in cases? Is vaccination coverage the only explanation? 20 Minutes make the point.
What are meningococci and which areas are affected?
There are several types of meningococci. “The most common in France are group B, C, W and Y meningococci, details the ministry. These are bacteria normally present in the throat and nose of many people. These bacteria can be transmitted through the air or through saliva. Transmission is human-to-human and requires close (less than 1 meter) and prolonged contact.
“Most often, meningococci do not cause any particular diseases, rather infections with no or few symptoms, such as angina, explains Professor Daniel Floret, specialist in infectious diseases and vaccinology and vice-president of the Technical Commission for Vaccinations at there High Authority of Health (HAS). Natural infections that do not lead to serious disorders, but in some cases it can cause very serious illnesses such as meningitis or septicemia”.
And several cases of IMM have been identified locally in recent months. “Spatiotemporal groupings of IIM B were identified in 2022 in Auvergne-Rhône-Alpes and Strasbourg, where vaccination campaigns were set up among the population, indicates Public Health France. These situations seem to be contained, but they are being carefully monitored. These phenomena can occur randomly in connection with the emergence and local implantation of certain strains of meningococci”. In practice, “the epidemiology of IMMs is extremely fluctuating and unpredictable, adds Daniel Floret. When a new one appears and it is very virulent, it will locally lead to an increase in cases, this is a phenomenon observed for a long time”.
Why such a rebound this year? Should we be worried about it?
According to Public Health France, this increase “is not an unexpected phenomenon, after two years of low circulation of meningococci. Two hypotheses can be put forward: (on the one hand), a higher risk of infection resulting from reduced immunity in the population having been less exposed to meningococci between 2020 and 2022”. A direct effect of Covid-19: “At the height of the pandemic, when barrier gestures and social distancing were widely respected, the number of IMMs had dropped very significantly, and collective immunity with it. But this winter, behaviors changed, and the circulation of meningococci resumed, with contaminations which not only started to rise again, but which are also higher than before the pandemic, ”underlines Professor Floret.
Another explanation for this winter: “a more marked season in connection with the scale of epidemics of seasonal viral infections in 2022/2023, continues Public Health France, in particular infections by the influenza virus”. By what mechanism? “There is a correlation between epidemics of respiratory viral diseases, which damage the respiratory mucous membranes, and IMM: the viral infection alters the mucous membranes, which allows the meningococcus to cross them and pass into the blood, and thus lead to sepsis and meningitis, describes Professor Floret. But this year, there was a very strong epidemic of influenza and RSV infections [virus respiratoire syncytial, notamment responsable de la bronchiolite chez les enfants]. Hence this increase in IMMs”.
What about vaccination against these meningococcal infections?
To date, “thanks to vaccination, we have practically eradicated C meningococci,” says Professor Floret. The problem is B, the leading cause of IMM in children, at the origin of the cases identified in Auvergne Rhône-Alpes and Strasbourg. But also those of type W, which affects adolescents and young children, and Y, which affects older adults: while they had fallen to very low incidence rates, they are in the process of going up.
However, “only vaccination against meningococcal C is compulsory until the age of 2 for children born from January 1, 2018, recalls Professor Floret. From now on, it is recommended against IMI B in all infants according to the following scheme: a first dose at 3 months, a second at 5 months, and a booster dose at 12 months. It is fundamental to improve vaccination coverage, which is probably low today, since this is the age group where the incidence of IMM B is highest, therefore all children under 2 years of age should be vaccinated against this strain. “The rebound observed in 2022-2023 is a reminder of the importance of vaccinating infants to protect them against infections linked to serogroups B and C”, abounds Public Health France.
For a more effective fight, “the HAS is asking itself the question of modifying the vaccination recommendations, in order to introduce protection against the W and Y strains, but also against the B strain” beyond 2 years, informs the vice – President of the Technical Commission for Vaccinations. “The reflection is in progress”.
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