The younger they are, the higher their chance of hospitalization. This is the conclusion of a study conducted by the University of Pisa and published in The Lancet Regional Health - Europe. The study examined infants treated by family pediatricians in Italy who were infected with respiratory syncytial virus (RSV). The risk of hospitalization is mostly connected with age, with an estimated likelihood of 12.5% at birth and gradually decreasing over time. "We conducted the study prior to the commencement of immunization campaigns in Italy with the new monoclonal antibodies against RSV, which were introduced in 2024-2025", explains Caterina Rizzo, research coordinator and professor at the University of Pisa. "These results are therefore beneficial for the prospective assessment of the efficacy of new preventive strategies. Estimating the risk by age group is critical for accurately assessing the clinical and economic impact of these instruments". Respiratory syncytial virus (RSV) is the main cause of respiratory tract infections in children under the age of five, with nearly all contracting it by their second birthday. The most severe forms of RSV may necessitate hospitalization, particularly in neonates and infants. In recent years, additional preventive methods have been launched, such as monoclonal antibodies delivered to newborns and a vaccine for pregnant women, making solid statistics on the disease's real impact even more essential. The study included 1,410 children with acute respiratory infections recruited through a network of private clinicians in five Italian regions—Tuscany, Lazio, Liguria, Lombardy, and Puglia—over four winter seasons from 2019 to 2024, excluding the 2020-2021 pandemic season. Researchers obtained clinical data from each child with confirmed RSV at the onset of illness, as well as at 14 and 30 days. RSV was determined to be the cause of infection in around 40% of cases. In children with a confirmed diagnosis, the sickness lasted an average of more than two weeks: on day fourteen, 41% of children still had symptoms, and 15% still had them on day thirty. 4.4% of RSV-positive children needed to be hospitalized, with a median stay of five days.