Resurgence of respiratory syncytial virus after COVID-19 pandemics-was there a change in seasonality?

ABSTRACT

Background: Respiratory syncytial virus (RSV) is the main cause of acute bronchiolitis. The peak of the infection is historically described in the autumn/winter season. The 2020 COVID-19 pandemic seems to have modified the seasonality of some respiratory viruses. The first case of SARS-CoV-2 infection diagnosed in Portugal was in March 2020. School closure and the use of masks are some of the pointed reasons for a decreased number of RSV infections observed in the autumn/winter season post the beginning of the pandemic. Interestingly, there are now a few studies from around the globe showing the resurgence of RSV infections in the spring/summer season that followed. Aim: To characterize the population of RSV infected infants admitted to a tertiary hospital before and after the beginning of the COVID-19 pandemic. Methods: A retrospective, descriptive, study was performed. All the RSV infected infants who were admitted to a Portuguese tertiary hospital from January 2017 to August 2021 were evaluated. The diagnosis of RSV infection was made through polymerase chain reaction of nasal secretions. Data such as age, gender, reason for admission, comorbidities, viral coinfection, bacterial superinfection, oxygen therapy, admission at Intensive Care Unit, ventilatory support and length of hospital stay were analyzed. Results: The data of a total of 354 patients was analyzed. The median age was 4 months (min 9 days, max 4 years), 50% were male. Before the COVID-19 pandemics (between 2017 and 2019), the peak of RSV infections used to occur in the months of December and January (medium of 25 and 28 cases per month, respectively). However, in December 2020 and January 2021 there was no detection of RSV. Nonetheless, a peak of RSV infection was verified in July and August 2021 (18 and 15 cases per month, respectively). The number of patients admitted for non-respiratory motifs, but in whom RSV was detected during the course of hospital stay, increased in 2021 (39%), comparing to 2017 (0%), 2018 (3%), 2019 (8%) or 2020 (3%), p<0,05. The number of viral coinfections was higher in 2021 (50%) comparing to 2017 (29%), 2019 (19%) or 2020 (18%), p<0,05. The patients admitted in 2021 were older (12 months average) than patients admitted in 2017 (5 months average) or 2018 (6 months average), p<0,05. Conclusions: RSV seasonality was modified by the COVID-19 pandemic, with an increase of the hospital admissions being registered in the summer of 2021. Our tertiary hospital's numbers reproduce what is being described in other places of the world. Subsequent studies are needed to verify the behavior of RSV infections in the next seasons, to understand if RSV infections are becoming more or less severe and to analyze the impact of SARS-CoV-2 virus on the virulence of RSV.