The flu season we are leaving behind will be remembered in many countries as one of the most intense in recent years. In Italy, certifies the latest report from the ISS that monitors the trend of seasonal infections every week, the record number of 16,129,000 was reached, "never reached in previous flu seasons" , surpassing another record, that of last year, with about a million and a half more cases. A figure that belies the estimates from the beginning of the season when a lesser impact was expected.

Last year, after two years in which measures to combat the pandemic had stopped the circulation of influenza viruses and respiratory viruses in general, a very intense season was observed almost everywhere. For this reason, many predicted a slowdown for this year. This was not the case.

In the United States, already in the middle of winter, there were those who spoke of the worst flu season in decades . The estimates elaborated at the end of April by the Centers for Disease Control and Prevention (CDC) seem to confirm it: there are between 47 and 82 million people affected; between 610 thousand and 1.3 million hospitalizations and between 26 thousand and 130 thousand deaths. Among these, at least 216 minors have already been confirmed.

In recent days, the European Centre for Disease Prevention and Control (ECDC) confirmed that 2024/2025 was "an intense influenza season" also in the European Union and the European Economic Area.

According to Gianni Rezza, associate professor of Hygiene at the Vita-Salute San Raffaele University in Milan, the reason for this year's record numbers is above all the mix of viruses that have been circulating . "Last year we were mainly dealing with influenza A viruses of the H1 type, responsible for about 90% of cases," he explains. "This year there was no such dominant strain; a third of the cases were caused by influenza A/H1 viruses, a third by influenza A/H3 viruses and a third by influenza B viruses. This means that a large portion of the population was susceptible to these agents," he continues. To these, then, are added the other respiratory viruses that circulate in the winter whose overall impact is greater than the influenza viruses. "Two in particular have played an important role: rhinovirus and respiratory syncytial virus," concludes Rezza.