“An upward recovery in flu indicators is still possible in the coming weeks.” This is what Public Health France wrote January 18. The national health agency was right. The flu epidemic slowed down last January. But, after four consecutive weeks of decline, it has been on the rise for three weeks.
This increase in contamination concerns nine of the thirteen metropolitan regions, particularly in Provence-Alpes-Côte d’Azur, which is one of the most affected regions, along with Auvergne-Rhône-Alpes and Occitanie. In mainland France, only Normandy and Hauts-de-France appear in the “post-epidemic” phase during which the end of the epidemic is possible in the short term.
However, the increase is less strong than in previous weeks, explained this Wednesday, February 15 Public Health France in its weekly report on week 6. Last week was marked by a “continued increase in all influenza indicators in all age groups but less marked” than the previous week, summarized the public health agency.
“B/Victoria”, this strain responsible for the second wave
The “viral circulation is mainly maintained by young people who are little or not vaccinated”, notes infectious disease specialist Benjamin Davido to L’Express. “This season, we are witnessing two waves of influenza because the epidemic started particularly early. The circulation was longer and more sustained this winter, whereas if the circulation of the virus is done over a shorter period of time, that little room for a second wave”, explains the Covid-19 referent medical director at the Raymond-Poincaré hospital in Garches (Hauts-de-Seine). Above all, Benjamin Davido notes that the lifting of barrier gestures due to the lull on the front of the Covid-19 epidemic allows “infectious agents”, such as the flu, to find a more favorable ground for its spread.
The epidemic was relaunched in particular by the expansion of a new strain, known as type B/Victoria. This is at the origin of a “sporadic epidemic outbreak”, believes Benjamin Davido, while the A (H3N2) strain, the first to strike, has “a higher rate of transmission”. “The relative share of type B/Victoria virus is progressing in the city but type A viruses are still present. In the hospital, type A viruses remain in the majority (57% in week 6) with a recent trend towards increase in the proportion of type B virus”, observes Public Health France.
“This is a second wave” of influenza carried by type B, considers Benjamin Davido. “It’s a bit like the emergence of a new variant,” he illustrates. “The population was mainly exposed to influenza A, but it is not because we had influenza A that we are therefore immune to influenza B”, recalls the infectiologist. It is therefore possible to catch the flu twice during this winter, even if it is infrequent.
In winter 2017-2018, already, type B of the flu had taken precedence over type A during week 5 of January, thus becoming the majority in early February. “We are really in the same conditions as in 2017-2018”, insists Benjamin Davido. The flu epidemic observed this season “is a copy and paste of what happened” five years earlier, notes the infectiologist, with a strong surge in contamination from the end of November and the beginning of December in the two cases.
Increased severity this season
At the hospital, the number of visits to the emergency room and hospitalizations after passage were “increasing in all age groups and more particularly among 0-14 year olds and 65 year olds and over for hospitalizations, respectively + 25 % and + 23 %”, indicates Public Health France. The share of influenza/influenza-like illness hospitalizations “continued to increase” between February 8 and 14, “going from a low to moderate level of intensity in all age groups”.
This season, the flu epidemic is also characterized by a fairly high severity. “The 2022-23 epidemic, which entered its 12th week in week 6, is characterized by marked severity, particularly among 15-44 year olds and 45-64 year olds”, she underlines. This severity is greater than during the 2019-20 and 2021-22 epidemics, but comparable to 2017-18, and lower than 2016-17 and 2018-19, specifies Public Health France.
“The epidemic rebound observed since week 4, mainly driven by the B/Victoria virus, is reflected in a significant impact in terms of severity (hospitalizations and deaths), including among those aged 65 and over, but less compared to levels observed during the epidemic peak at the end of December 2022”, also notes the agency.
Vaccination campaign extended in February
On January 20, even before the resumption of the flu epidemic, the health authorities announced an extension until February 28 of the national vaccination campaign against seasonal flu. A “good answer”, believes Benjamin Davido, who also pleads for the vaccination of children against this virus. This could be the case at the end of 2023.
On February 9, the High Authority for Health (HAS) recommended “that vaccination against seasonal flu be integrated into the vaccination schedule to be offered each year to children without comorbidities aged 2 to 17 years old, without making it compulsory. “.
Concretely, if this proposal were retained by the government, it would mean that from the age of two, all minors could be vaccinated against the flu every year, as is already the case for people over 65. .
To support the individual interest of the vaccine in the youngest, the HAS insists in particular on the fact that the under 15s have accounted for a lot in the hospitalizations linked to the flu during the last epidemics. This large proportion of hospitalized children is mainly due to the fact that the oldest are widely vaccinated, and therefore less prone to complications, rather than to a particularly high dangerousness of the current viruses in the youngest.