Background/Objectives: Respiratory syncytial virus (RSV) is a leading cause of respiratory infections across all age groups, with the greatest burden observed in young children and older adults. The COVID-19 pandemic significantly disrupted RSV circulation, resulting in an immunity gap and altered transmission dynamics. This study aimed to assess the seroprevalence of anti-RSV IgG antibodies in the Polish population during the 2023/2024 epidemic season. To our knowledge, this is the first study to characterize RSV seroprevalence at the population level in Poland. Methods: A total of 700 serum samples from individuals across different age groups were analyzed using a commercial assay to detect anti-RSV IgG antibodies. Seroprevalence and antibody levels, expressed as the index of positivity (IP), were examined by age and sex. Results: The overall seroprevalence of anti-RSV IgG antibodies was 91.4%. Antibody positivity increased markedly from 35.5% in infants aged 0–1 years to over 90% in children aged 4–5 years, reaching nearly universal levels in older age groups, including 99.1% in adults aged ≥60 years. Median IP values also rose with age, peaking in individuals aged ≥60 years. No significant differences in seroprevalence were observed between sexes, though older men showed slightly higher median IP values, potentially reflecting greater cumulative RSV exposure. Conclusions: This study provides key insights into the post-pandemic landscape of RSV immunity in Poland. The high seroprevalence across most age groups underscores widespread prior exposure, while the lower rates in infants highlight a continued vulnerability. These findings support the development and implementation of targeted immunization strategies, particularly for infants and older adults.

Respiratory syncytial virus (RSV) is a significant cause of respiratory infections across all ages. However, data on the circulation of its antigenic subgroups, RSV-A and RSV-B, remain limited in certain regions, including Poland. Therefore, this study provides the first molecular insight into the post-pandemic circulation of RSV subgroups in Poland. We analyzed 377 RSV-positive respiratory samples collected across Poland during three consecutive seasons (2022/23, 2023/24, and 2024/25) using qRT-PCR to determine subgroup distribution. An equal prevalence of RSV-A and RSV-B was observed in 2022/23, followed by RSV-A predominance in 2023/24 and a shift to RSV-B dominance in 2024/25. Individuals infected with RSV-A were significantly younger than those infected with RSV-B, a pattern evident in the latter two seasons but not in 2022/23. In general, adults (≥18 years) had higher odds of RSV-B infection (OR = 2.35, 95% CI: 1.44–3.84; p = 0.006). Coinfections with both subgroups increased from 5% in 2022/23 to approximately 15% in later seasons, and were more frequent in women. Coinfections with influenza viruses or SARS-CoV-2 were infrequent and showed no statistically significant differences between seasons. The findings of the present study highlight dynamic, region-specific RSV epidemiology and underscore the importance of sustained molecular surveillance to inform public health preparedness and guide emerging RSV immunization strategies in Poland.

In Poland, flu supervision is coordinated by the National Influenza Center at the National Institute of Public Health—National Institute of Hygiene. In this publication, we want to determine geographical trends in influenza virus circulation in the region. A detailed analysis of virological and epidemiological data showed the course of the epidemic season in Poland, as well as in neighboring countries. The spatial differentiation of the incidence of infection between voivodships was examined, as well as compared to countries that border a given voivodship. The results show a significant variation in the incidence of infection in terms of time and space. This points to the need to increase the number of tests and to raise awareness among health care professionals and the public about the probability of an influenza pandemic, as undetected viruses can spread further into the European Union.

Respiratory Syncytial Virus (RSV) is a prevalent pathogen of the respiratory tract, posing a significant threat to individuals with compromised immune systems, particularly the elderly and neonates in hospital settings. The primary objective of this study was to identify a specific period within the epidemic season during which healthcare providers can anticipate an increased incidence of RSV infections and characterize the epidemic season in Poland. Molecular biology techniques were employed to diagnose samples at Sanitary Stations and the National Institute of Public Health (NIC) in Warsaw. Epidemiological data were collected using the SENTINEL surveillance system. In the 2020/2021 season, there were no reported cases of RSV due to the prioritization of SARS-CoV-2 diagnostics. Before the pandemic, the period of heightened RSV infection risk typically commenced in the 51st week or later, with a statistically significant correlation indicating that a later start was associated with a shorter season duration (p = 0.034). In post-pandemic seasons, the temporal distribution of RSV cases exhibited a notable shift, with earlier season onset, peak, and conclusion. Data indicate that RSV is predominantly diagnosed in pediatric populations; however, since the 2017/2018 season, there has been an increase in RSV diagnoses among other age groups. Given the observed shifts in the seasonal peak following the SARS-CoV-2 pandemic, ongoing surveillance is required to ascertain whether these changes are permanent or transient.