The administrative language of the High Authority for Health (HAS) sometimes presents sibylline subtleties. So it is, for example, of its opinion published on February 9 on the vaccination of children against influenza. Contrary to what has been reported here or there, its experts do not recommend mass vaccination of children under 18 against this infection. No, they just say that this injection should “be offered to them every year”. A nuance that turns out to be very important: “This is clearly a half-hearted recommendation. There are elements in favor of this vaccination, but there are also unknowns, and therefore uncertainties about its long-term relevance. “, decodes Professor Jean-Daniel Lelièvre, head of the immunology and infectious diseases department at the Henri-Mondor hospital in Créteil (AP-HP) and expert for the HAS.
“Indeed, this is not a strong recommendation. We are simply saying that parents wishing to have their children vaccinated should be offered this possibility, with reimbursement of the vaccine”, specifies Professor Élisabeth Bouvet, who chairs the Technical Commission on Vaccinations. (CTV) of the HAS. No obligation, not even an incentive. But a change of direction nevertheless, while many countries already protect their children against the flu, sometimes for a long time: many European states, but also the United States, the United Kingdom, Canada or New Zealand . And for good reason: “At least half of the cases of influenza identified each year are found in children, who are the main vectors of the epidemic”, recalls Professor Antoine Flahault, epidemiologist and director of the Institute of Health global at the University of Geneva (Switzerland). This expert had already shown several years ago that closing schools during school holidays broke the dynamics of the epidemic and saved lives, especially among the oldest.
“Various studies indicate that from 10% to 15% of the pediatric population covered, the epidemic peak decreases”, underlines Professor Bouvet. Data confirmed by the experiences of countries that have already adopted this measure. “The United Kingdom, when rolling out childhood vaccination, showed an indirect effect on adults by comparing pilot areas, where immunizations were already performed, with those that were not yet vaccinating. In Japan, where children were vaccinated between 1970 and 1990, during this period we observed a drop in excess mortality due to pneumonia and influenza in the population as a whole, and an increase when the program stopped”, explains Marc Baguelin, researcher at Imperial college in London, and a member of the CTV. This effect would be above all linked to the interruption of the chains of transmission: “It is approximately linear with the proportion of vaccinated children. Of course, the higher their number, the greater the impact for the population will be”, specifies the epidemiologist.
Many unknowns
Added to this is an easing of the pressure on hospitals: it is also because pediatric establishments were overwhelmed this winter by the “triple epidemic” of bronchiolitis, Covid and influenza that the Ministry of Health requested the High Authority for Health to decide on this flu vaccination. In addition to these “altruistic” advantages, children find benefits for themselves, with a reduction in serious forms, even if these remain rare, and fewer school days lost. So many undeniable advantages, while in addition, the flu vaccine is particularly safe. Under these conditions, why did the French experts not give a more affirmative opinion, recommending, for example, an organized campaign, like the one intended for adults at risk of serious forms?
Because of the unknowns linked to repeated vaccination year after year in children for fifteen years, answers Professor Lelièvre: “At this stage, we do not know exactly what the consequences would be in terms of long-term efficacy”. In question, according to this expert, a complex phenomenon called “immune fingerprint”, which could make the injections less effective over time. It is linked to more or less significant variations in the flu strains in circulation from one year to the next. Immunity retains a strong memory of its first contact with a pathogenic agent, and would tend to reinforce this first memory with each vaccination, rather than producing antibodies against new variants of the virus, in particular when these are not not very different from the first.
“We cannot say whether to vaccinate every year, or only in the event of significant changes in the viral strain, for example”, indicates Professor Lelièvre. Hence the impossibility, for the HAS, to come out in favor of a campaign in good and due form, even if the vaccine should nevertheless be included in the vaccination schedule. “In a country where, moreover, vaccine hesitation can be strong, we especially wanted parents to begin to be made aware of this possibility”, adds Elisabeth Bouvet.
The parent’s dilemma
Parents, precisely, risk feeling a little lost in view of these uncertainties… “There is no hesitation for children suffering from illnesses exposing them to serious forms of influenza: for them, the benefit of a vaccination is very important. The same is true for those living in the entourage of subjects at risk. If their slightly elderly and sick grandparents look after them regularly, it may be quite appropriate to vaccinate them”, answers Professor Lelièvre.
In the field, pediatricians do not say anything else. Dr. Andreas Werner, based in Vaucluse and president of the French Association of Ambulatory Pediatrics, explains that he will recommend immunization, but without insisting: “There are injections that I push a lot with my patients, like the one against the HPV virus responsible for cancers, or against meningococci which cause meningitis. Against the flu, it will depend on the context of the families”. However, he indicates that he is relieved to see this vaccine soon reimbursed: “I recommend it in particular when a newborn baby arrives, to offer indirect protection to the baby. But when it is necessary to protect the parents and a whole sibling, the the addition climbs quickly”.
On the other hand, the vaccination itself should not be too difficult to make children accept, provided that the only intranasal vaccine authorized in France finally arrives on the market. The High Health Authority has in any case heavily insisted on this in its opinion. “The manufacturer who produces it does not market it in France at the moment. We hope that the reimbursement, to which our recommendation paves the way, will facilitate its arrival in our country”, underlines Professor Elisabeth Bouvet. The little ones would appreciate it all the more since before the age of nine, the first administration of an injectable flu vaccine must be done in two injections, one month apart…