The younger the child, the higher the risk of hospitalisation. This is the key finding of a study coordinated by the University of Pisa and published in The Lancet Regional Health – Europe, which analysed children followed by primary care paediatricians in Italy and affected by respiratory syncytial virus (RSV). Age emerges as the main factor associated with the risk of hospitalisation, with an estimated probability of around 12.5% at birth, progressively decreasing with age.
“We conducted the study before the launch in Italy of immunisation campaigns using the new monoclonal antibodies against RSV, introduced in 2024–2025,” explains Caterina Rizzo, Professor at the University of Pisa and coordinator of the research. “These results are therefore useful for assessing, in the future, the effectiveness of new preventive strategies. Estimating risk by age group is essential for properly evaluating the clinical and economic impact of these interventions.”
Respiratory syncytial virus is one of the leading causes of respiratory infections in children under five years of age: almost all children contract it by the age of two. In its more severe forms, it can require hospitalisation, particularly in newborns and infants. In recent years, new preventive tools have been introduced, including monoclonal antibodies for newborns and a vaccine for pregnant women. This makes it even more important to obtain reliable data on the true burden of the disease.
The study involved 1,410 children with an acute respiratory infection, enrolled through a network of family paediatricians in five Italian regions — Tuscany, Lazio, Liguria, Lombardy and Apulia — over four winter seasons between 2019 and 2024, excluding the 2020–2021 pandemic season. For each child with a confirmed RSV infection, researchers collected clinical data at the onset of the disease and again after 14 and 30 days. RSV was responsible for approximately 40% of cases.
On average, the illness lasted more than two weeks among children with a confirmed infection: 41% of children still showed symptoms on day 14, and 15% remained symptomatic on day 30. Overall, 4.4% of RSV-positive children required hospitalisation, with a median hospital stay of five days.
The study also found that, although fever is common in RSV-positive children, it does not allow the infection to be distinguished from other respiratory viruses. Consequently, epidemiological surveillance systems that require the mandatory presence of fever may fail to detect a significant proportion of cases, leading to an underestimation of the disease’s true impact.
This research was conducted as part of the European RSVComNet project and involved universities and hospital centres in Pisa, Rome, Genoa, Bari and Milan. Although funding was provided by Sanofi and AstraZeneca, the authors independently conducted the data collection, analysis and interpretation of results, and made the decision to submit the study for publication.
