Late Breaking Abstract - Impact of COVID-19 social distancing on viral infection in France: a delayed outbreak of RSV

COVID-19 pandemic and associated lockdown measures has deeply modified the natural course of seasonal viral infections, such as respiratory syncytial virus (RSV). Methods: Using French national data from 3 networks: emergency departments (ED), general practitioners (GP), and hospital laboratories, we compared the number of ED visits and GP visits for bronchiolitis in children <2 years of age, and the percentage of RSV positive tests in the 2020-2021 season with those of the two previous seasons (2018-2019 and 2019-2020). Results: During the 2020–2021 season, the epidemic begun in February (week 05) in the Ile de France (Paris and suburbs) region, 12 weeks later compared with the previous seasons. The highest number of bronchiolitis cases in 2021 (week 12) occurred 10-12 weeks after the previous seasonal peaks of previous seasons, but the number of cases remained lower than in the previous seasonal peaks. By the end of March 2021, the percentage of RSV positive tests rose from 3 % in week 4 (125/4734) to 11 % in week 13 (612/5600), higher than that observed in week 13 in 2019 and 2020 (1% and 0 % respectively), but lower than that during the peak weeks of the previous two seasons (21% in week 49-2019 and 27% in week 50-2018). Meanwhile, rhinovirus, positivity rate was highest at 30% in week 42 in 2020, followed by a decline at 15% in weeks 42-52 in 2020 and remained stable during weeks 01-19 in 2021 with a median of 11% (range 8%-13%). Conclusion: We identified a delayed RSV epidemic in the period that usually corresponds at the end of the epidemic season, raising concerns for the burden of RSV in the already strained healthcare systems during the COVID-19 pandemic.