Katarzyna Łuniewska

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.

BACKGROUND The SENTINEL influenza surveillance system has been used in Poland since 2004, incorporating both epidemiological and virological monitoring of influenza viruses. SENTINEL works in cooperation with general practitioners, 16 Voivodship Sanitary Epidemiological Stations (VSES), and the National Influenza Centre (NIC). NON-SENTINEL samples are collected from places that do not participate in the SENTINEL program. This enables continuous observation of virological and epidemiological situation in the country. The aim of the study was to conduct a comparative analysis of circulating influenza and influenza-like viruses during the 2022/2023 and 2023/2024 epidemic seasons, as monitored through the SENTINEL and NON-SENTINEL surveillance systems in Poland. MATERIAL AND METHODS The study material consisted of nasal and throat swabs collected by the VSES. Molecular biology methods were employed for virus detection and identification. The analyses were based on data obtained from the SENTINEL system for the 2022/2023 and 2023/2024 epidemic seasons. RESULTS During the 2022/2023 epidemic season, co-dominance of the A/H1N1/pdm09 and A/H3N2/subtypes was noted, whereas the 2023/2024 epidemic season in Europe was dominated by the A/H1N1/pdm09 subtype. Among the influenza-like viruses, SARS-CoV-2 and RSV were the most frequently detected in both epidemic seasons. CONCLUSIONS The influenza surveillance system in Poland enables continuous, weekly monitoring of the epidemiological situation throughout each season. This allows for a rapid response in the event of the emergence of new influenza virus variants. The results obtained as part of influenza surveillance in Poland are consistent with those observed in other European countries.

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.

The aim of this study was to determine the level of anti-hemagglutinin antibodies using the hemagglutination inhibition test (HAI) in the blood sera of patients collected during the 2023/2024 epidemic season in Poland. This data is valuable for assessing the level of population immunity to influenza viruses circulating in Poland during this epidemic season. The study material consisted of serum samples collected across the country and divided into seven age groups. The test results confirmed the presence of anti-hemagglutinin antibodies for the antigens included in the quadrivalent influenza vaccine recommended by the World Health Organization (WHO) for the 2023/2024 epidemic season: A/Victoria/4897/2022 (H1N1)pdm09, A/Darwin/9/2021 (H3N2), B/Austria/1359417/2021 (B/Victoria lineage) and B/Phuket/3073/2013 (B/Yamagata lineage). The highest values of the geometric mean (GMT = 121.0 [95% CI: 108.5–134.9]) and protective factor (70 [95% CI: 67–74]%) were recorded for the A/H3N2/influenza virus antigen. In Poland, the vaccination rate of the general population in the discussed season was only 5.52%. The obtained results can therefore be interpreted as a response of the immune system, consisting of the production of anti-hemagglutinin antibodies in patients who had previously had an infection caused by the influenza virus.

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.

Background: The aim of this study was to determine whether the occurrence of the SARS-CoV-2 pandemic affected the incidence of influenza in Poland and the efficiency of the SENTINEL influenza surveillance system. Methods: The analysis was based on virologic data from the 2018/2019–2021/2022 epidemic seasons. The data in question were obtained from the SENTINEL influenza surveillance system, which is utilized in Poland. Results: In the 2020/2021 epidemic season, only one positive case was confirmed. In the epidemic season of 2021/2022, the number of positive cases increased. There was a delay in the peak of the season, since the start of pandemic, which was observed in the 14th week of 2022. Previously, it was recorded in the 5–10th week, depending on the season. Before the pandemic, the number of positive samples in relation to the tested ones oscillated between 41–49.4%. After the pandemic, it was 0.3% and below 20%, respectively, for season 2020/2021 and season 2021/2022. Conclusions: The COVID-19 pandemic caused a decline in many other infectious diseases, including influenza, as a result of the numerous lockdowns and from people shifting to remote work. Other safety measures, such as obligatory protective masks and the use of disinfectants, had a significant impact on reducing the number of cases.

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.

Subtypes of Influenza Virus Infection and Outcomes in Individuals Older than 65 Years of Age in Poland in the 2016/2017 to 2019/2020 Epidemic Seasons - Article abstract #929243

The aim of this study was to determine the level of antibodies against hemagglutinin of influenza viruses in the sera of people in the seven age groups in the epidemic season 2018/2019 in Poland. The level of anti-hemagglutinin antibodies was determined by hemagglutination inhibition test (HAI). 1050 clinical samples from all over the country were tested. The level of antibodies against influenza viruses was highest in the 10–14 age group for A/Singapore/INFIMH-16-0019/2016 (H3N2) and B/Phuket/3073/2013 Yamagata lineage antigens. These results confirm the circulation of four antigenically different influenza virus strains, two subtypes of influenza A virus – A/Michigan/45/2015 (H1N1)pdm09 and A/Singapore/INFIMH-16-0019/2016 (H3N2) and two lineages of influenza B virus – B/Colorado/06/2017 – Victoria lineage and B/Phuket/3073/2013 Yamagata lineage.

This study seeks to define the level of antihemagglutinin antibodies, using the hemagglutination inhibition assay (HAI), in the serum of patients, stratified into seven age groups, in Poland during the influenza epidemic season of 2017/18. A quadrivalent influenza vaccine has been introduced in Poland as of this epidemic season, making it possible for the first time to conduct the analysis for four antigens: A/Michigan/45/2015 (H1N1) pdm09, A/Hong Kong/4801/2014 (H3N2), B/Brisbane/60/2008 – Victoria lineage, and B/Phuket/3073/2013 – Yamagata lineage. We found that the level of individual antihemagglutinin antibodies was different among the seven age groups studied; with the highest in patients of 5–9 years and 10–14 years of age. Interestingly, the protection factor, defined as the percentage of people with the level of antihemagglutinin antibodies of at least 1:40 after vaccination or due to a previous infection, was the highest for the antigen A/Hong Kong/4801/2014 (H3N2) in the same age groups (74% and 75%, respectively). Taking into account the dismal 3.6% of the vaccinated population in Poland, these findings point toward the sustained presence of an immune system response in patients after a prior influenza virus infection.