COVID-19 restrictions’ impact on epidemiology of respiratory syncytial virus in south-eastern Poland

Introduction
Respiratory syncytial virus (RSV) is a serious healthcare problem in Poland and one of the most common causes of lower respiratory tract infections in young children. During the pandemic, coronavirus disease 2019 significantly reduced the number of RSV cases due to restrictive measures to reduce social contact. The coronavirus disease 2019 pandemic led to widespread changes in health and social functioning, including restricted access to medical services and the closure of schools and workplaces. Non-pharmaceutical interventions significantly altered the seasonality and epidemiology of RSV. Recent years have shown a shift in the dynamics of RSV infections in children in the south-eastern region of Poland. The observed changes, particularly in the number of infections and related hospitalizations during autumn and winter, provide an opportunity to better understand RSV transmission patterns.

Material and methods
Analyses were conducted in R 4.3.2. (R Core Team, 2024). Descriptive statistics were used, and temporal trends were assessed with line-point plots based on absolute and relative monthly counts, adjusted for calendar days and leap years (lubridate package).

Results
This study included 1804 RSV cases with a median age of 5 months (interquartile range – IQR: 2–14, range 1–117). Males predominated (n = 1010, 55.9%). The median hospital stay was 6 days (IQR 4–8). Among hospitalized patients (n = 1466, 81.3%), diagnostic lag was most often zero (n = 1211, 82.6%), with only 55 cases (3.8%) exceeding 7 days (range 30–81).

Conclusions
These findings may support changes in the timing and criteria for immunoprophylaxis. Based on our results and similar data from other countries, we propose revising prophylactic recommendations to better protect children in the post-pandemic era.