A new variant of respiratory syncytial virus (RSV)-B was the most common in Italy after the pandemic

What is it about?

Respiratory syncytial virus (RSV) is a main cause of severe lower respiratory tract infection in infants and the oldest. During the first phase of the pandemic, there were few cases of RSV because of non-pharmaceutical interventions to control SARS-CoV-2. After the pandemic restrictions eased in autumn 2021, RSV caused more infections than before. In north-central Italy, subtype-A mainly caused cases in hospitalised patients, while RSV-B was more common in outpatients with flu-like symptoms. In the 2022-2023 autumn/winter season in north-central Italy, subtype-B was the most common in both inpatients and outpatients, and infected more adults than in the previous season. The analysis of the more variable RSV protein showed that RSV-A strains were not much different from those before the pandemic. Our study found a new type of RSV-B virus, different from the ones in Italy before the pandemic. The genetic divergence of RSV-B may have increased the risk of infection, contributing to the high number of cases in 2022-2023. This was also seen in other European countries.

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Why is it important?

Studies on SARS-CoV-2 variants have shown that there are still lots of unknowns about other respiratory viruses, and RSV in particular, which is a main cause of hospitalisations in children and adults. Our study adds new elements to our understanding of the mechanisms that cause RSV variants to circulate. It's important to increase epidemiological surveillance of RSV at the national level and to carry out genomic sequencing projects at the local level. This would help us to keep an eye on how infectious and dangerous different RSV strains are, and to predict how many cases we’ll see during the next season. This would help us to make sure we’re using our healthcare resources in the most effective way.

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