While the coronavirus is circulating less and the bronchiolitis epidemic is improving, remaining at a high level, influenza indicators were increasing throughout France at the end of 2022. The Minister of Health , François Braun, warned, Wednesday, December 28, against “a week of all dangers”. “There is an explosion of cases [de grippe]with also serious cases, which mean that the resuscitation services in a global way are saturated “, said the former emergency doctor. Hospitalizations for flu-like illness have indeed increased by 75%, said Public Health France (SPF) in its latest epidemiological bulletin.
Several indicators show the precocity of the flu this season. According to data from the Sentinelles network, which brings together more than 1,300 private general practitioners, the rate of consultations for flu-like illness was estimated at 460 per 100,000 inhabitants for the penultimate week of 2022. A very high figure for this period of the year, if compared to the last ten years, where the peak of the epidemic generally occurs between February and March.
The proportion of flu-like illnesses among SOS Médecins consultations also provides information on the extent of the epidemic. For eight consecutive weeks, these consultations have been increasing and occur much earlier than in previous years.
The share of hospitalizations for influenza at the highest since 2010
Hospital data also show the epidemic picking up speed. In all age groups, the number of visits to the emergency room for influenza continued to increase (+ 52% compared to week 50), as did the number of hospitalizations after a visit to the emergency room for influenza (+ 75% In a week).
The health authorities note that, the week of December 19, the share of hospitalizations for influenza or influenza-like illness reached 41.2 per 1,000 hospitalizations for all causes combined, i.e. the “highest value observed for this indicator during the period 2010-2023”.
Since October 3, at least 193 serious cases of influenza have been admitted to intensive care, including 142 since December 5. Among them, we find mainly seniors (80 were 65 or over), but also younger ones: 16 were between 0 and 4 years old, 16 between 5 and 14 years old and 79 between 15 and 64 years old, according to the weekly bulletin, which specifies that these data are based on around forty intensive care units and are not exhaustive.
A rising positivity rate
Like the SPF nuance, certain indicators used for flu surveillance are based on the symptoms of patients, which tends to bias the data during the Covid-19 pandemic. “It is therefore likely that some of the cases of influenza-like illnesses reported by our influenza surveillance are due to Covid-19 and not to influenza”, specifies the organization.
“This is the ambiguity of the expression ‘flu syndrome’, which can relate to several illnesses, commented Vincent Enouf, Deputy Head of the National Reference Center for Respiratory Infection Viruses at the Institut Pasteur. We must therefore look at the side of the tests, whose positivity rate for influenza has increased in recent weeks. » In city medicine, the Sentinels network reported a positivity rate of 65.3% in week 51, against 56% the previous week. In hospitals, the positivity rate was 20.1%, compared to 13.9% two weeks earlier.
“In the past, epidemics where H3N2 was the majority were stronger, more virulent and caused more deaths”
“We are facing the earliest flu epidemic in at least a decade.remarks Sibylle Bernard-Stoecklin, epidemiologist in the infectious diseases department of SPF. It came two weeks earlier than in 2017-2018, which was already one of the earliest. » A specificity which is observed elsewhere in Europe, in North America but also in Australia and New Zealand this summer, while the epidemic of last season was conversely very late – it had started in March. The epidemiologist, however, specifies that “the time of year when an influenza epidemic occurs is not necessarily correlated with its severity”.
Difficult to predict peak or durationepidemic
An observation shared by Vincent Enouf: “What will tell us if it is a major epidemic is the majority virus. » In mainland France, subtype A (H3N2) remains the most prevalent, although an increase in the detection of type B/Victoria viruses has been observed for several weeks. “A (H3N2) is a virus that evolves faster than others, adapts better and has a greater ability to escape the vaccineexplains the researcher from the Institut Pasteur. When we look at the past, the epidemics where A (H3N2) was predominant were stronger, more virulent and caused more deaths, especially among people at risk, as for the [coronavirus] SARS-CoV-2. »
“However, it is not because the A (H3N2) virus is in the majority at the start of the epidemic that it will remain so throughout the season, specifies Sibylle Bernard-Stoecklin. This is in particular why it remains very difficult to predict the peak of the epidemic or how long it will last: there may be a rebound carried by another virus. »
The flu causing between 10,000 and 15,000 deaths each year, according to the Institut Pasteur, the health authorities point to the” emergency “ to be vaccinated for people at risk and recall the importance of barrier gestures, especially during the end of year celebrations. In 2021-2022, only 56.8% of people over 65 were vaccinated against the flu. For this season, the figures are not yet known.