Influenza 2024, peak passed and H1N1 virus prevalent: “But it’s not over”

The ISS bulletin: sustained circulation is highly probable also in the coming weeks, in 5 regions the incidence threshold is ‘very high’

The peak of flu cases in 2024 has passed in Italy. In the last week, the 52nd from 25 to 31 December, there has been a “sharp decline in the number of cases of flu-like syndromes in Italy, but still in the high intensity range” with ‘traditional’ symptoms: fever, cold, fatigue , muscle pain, headache. “In the first week of 2024, the incidence dropped to 16.5 cases per thousand assisted, while in the previous week the peak was reached with 18.3. The proportion of influenza-positive samples out of the total samples analyzed also fell ( 34% versus 46%)”, according to the picture outlined by the RespiVirNet surveillance bulletins. In the last week, the estimated cases of flu-like syndrome, compared to the entire Italian population, are approximately 1,027,000 (they were 1,042,200 seven days before) for a total of approximately 6,719,000 cases since the beginning of the surveillance.

“Strongly probable strong flu circulation also in the coming weeks”

“Both the epidemiological and microbiological data seem to indicate that we are passing the peak, even if sustained circulation is highly probable also in the coming weeks, facilitated by the reopening of schools – comments Anna Teresa Palamara, who heads the Infectious Diseases department of the ISS -. We therefore continue to recommend vaccinations for the people most at risk, still useful in view of the ‘tail’ of the season which will still last several weeks, and healthy prudence in behavior. The recommendation not to take antibiotics, which are useless in case of viral infections, remains valid unless advised by your doctorand to go to the emergency room only if strictly necessary”.

Incidence slightly increasing only in children, stable in adults. ‘Very high’ intensity threshold in 5 regions

The incidence is slightly increasing only in children under five years of age where the incidence is equal to 48.7 cases per thousand assisted (47.5 in the previous week), stable in adults and the elderly. All the Regions and autonomous provinces, among those that have activated surveillance, record an incidence level of flu-like syndromes above the baseline threshold, except the province of Bolzano. In five Regions the threshold of ‘very high’ intensity of incidence was reached (Friuli-Venezia Giulia, Tuscany, Umbria, Abruzzo, Campania).

“Although it is always difficult to make predictions on the progress of the season, such a clear decline suggests that the peak has been reached – states Antonino Bella, head of RespiVirNet epidemiological surveillance and editor of the epidemiological bulletin -. However, upward fluctuations are possible ‘, especially in children, favored by the reopening of schools.”

H1N1 “largely prevalent” among influenza viruses

Among influenza viruses, “type A viruses are largely prevalent (99%) compared to type B viruses and mostly belong to the H1N1pdm09 subtype”, underlines the Higher Institute of Health. “Among the samples that tested positive since the beginning of the season, 19% were positive for Sars-CoV-2, 12% for Rsv (respiratory syncytial virus), 44% for influenza A, while the remainder tested positive for others respiratory viruses,” the report specifies.

“Virological data confirm that influenza viruses prevail among circulating respiratory viruses – states Simona Puzelli, head of RespiVirNet virological surveillance and editor of the virological report – In particular, among type A influenza viruses the prevalent subtype is H1N1pdm09, which represents 77 .7% of all influenza viruses identified so far in the 2023-2024 season.”