Epidemiology of respiratory syncytial virus in hospitalized children before, during, and after the COVID-19 lockdown restriction measures in Greece.

The COVID-19 pandemic modified the epidemiology and the transmission of respiratory syncytial virus (RSV). We collected data on RSV positivity and incidence from children hospitalized in the largest tertiary paediatric hospital in Greece before (2018-2020, period A), during (2020-2021, period B), and after (2021-2023, period C) the COVID-19 lockdown. A total of 9,508 children were tested for RSV. RSV positivity (%) was 17.6% (552/3,134) for period A, 2.1% (13/629) for period B, and 13.4% (772/5,745) for period C (p < 0.001). The mean age (±SD) of RSV-positive children among the three periods was A: 5.9(±9.3), B: 13.6 (±25.3), and C: 16.7 (±28.6) months (p < 0.001). The peak of RSV epidemiology was shifted from January-March (period A) to October-December (period C). RSV in-hospital incidence per 1,000 hospitalizations in paediatric departments was A:16.7, B:1.0, and C:28.1 (p < 0.001), and the incidence in the intensive care unit was A: 17.3, B: 0.6, and C: 26.6 (p < 0.001). A decrease in RSV incidence was observed during the COVID-19 lockdown period, whereas a significant increase was observed after the lockdown. A change in epidemiological patterns was identified after the end of the lockdown, with an earlier seasonal peak and an age shift of increased RSV incidence in older children.