Search Results (167)

Despite the persistent global threat of seasonal influenza viruses such as A(H1N1)pdm09 and A/H3N2, their epidemiological and genetic characteristics in China following the implementation of COVID-19 non-pharmaceutical interventions (NPIs) remain poorly characterized. Between September 2020 and December 2023, we conducted an integrated epidemiological and genomic analysis of influenza A viruses in children in Wuhan. The overall positivity rate for influenza A virus was markedly low at 3.43% (109/3171), reflecting a profound suppression of circulation during the pandemic. Among genotyped positives, H1N1pdm09 was predominant (52.3%), followed by H3N2 (16.5%) and untypeable strains (32.1%). Preschool children showed the highest susceptibility. Phylogenetic analysis revealed that the circulating H1N1 strains (90%) belonged to clade 6B.1A.5a.2, clustering with viruses from Hong Kong and Pakistan. In contrast, H3N2 strains (76.92%) primarily fell into clade 3C.2a1b.2a.2b, closely related to contemporary strains from Europe and North America. Notably, we identified key hemagglutinin mutations associated with antigenic drift (e.g., R240Q in H1N1; E78G, R158G in H3N2) and neuraminidase mutations potentially conferring antiviral resistance (e.g., S247N in H1N1; S245N, a putative novel glycosylation site, in H3N2). Evidence of reassortment events was also detected, underscoring the continued genomic evolution of these viruses despite their low prevalence. Our findings demonstrate that genetically diverse and antigenically drifted influenza A viruses continued to circulate and evolve in Wuhan during the COVID-19 pandemic, albeit at dramatically reduced levels. This highlights the critical need for sustained genomic surveillance and timely updates of vaccine compositions to pre-empt the resurgence of influenza in the post-pandemic era. Full article

Influenza viruses are characterized by their high mutation rates which require continuous molecular surveillance to ensure the annual effectiveness of influenza vaccines. The current study aimed to investigate the molecular evolution and vaccine match of the 2009 pandemic (A(H1N1) pdm09) virus circulating in Riyadh, Saudi Arabia. A total of 380 nasopharyngeal aspirates (NPAs) were collected during the 2020–2023 winter seasons from patients with influenza-like illness. Influenza A virus (IAV) detection, typing, and amplification of hemagglutinin (HA) and neuraminidase (NA) genes were achieved using one-step RT-PCR. The full-length HA and NA genes of 14 selected A(H1N1) pdm09 isolates were sequenced and used for sequence and phylogenetic analysis, which also included sequences of seven A(H1N1) pdm09 isolates collected in Riyadh during the 2024–2025 season. IAV was detected in 17.11% samples; A/H3N2 (9.21%) was somewhat more prevalent than A(H1N1) pdm09 (7.89%). Children aged 0–4 years had the highest incidence rate of infection. Comparing the HA1 domain of A(H1N1) pdm09 isolates circulating in Riyadh to the current vaccine strains (A/Wisconsin/67/2022 and A/Victoria/4897/2022), a total of 24 amino acid substitutions were identified. O-linked and N-linked glycosylation sites in the HA and NA proteins of the Riyadh isolates coincided with those of the two vaccine strains. The receptor-binding domain (130-loop) of the HA1 domain showed a persistent S137P substitution in all study isolates; this mutation is not present in the current vaccination strain. This finding suggests a potential antigenic mismatch between the current vaccine and the circulating A(H1N1) pdm09 strains in Riyadh, warranting hemagglutination inhibition (HAI) assays to confirm the impact of the S137P substitution on antigenicity and immune evasion. As shown above, ongoing molecular surveillance is essential for guiding the yearly selection of vaccine candidates to increase efficacy. Full article

Background/Objectives: Despite high vaccination coverage, influenza remains a public health concern in South Korea, particularly in older adults. Continuous evaluation of vaccine effectiveness (VE) is essential to optimize immunization strategies. Methods: This study evaluated seasonal influenza VE for preventing laboratory-confirmed influenza using a test-negative design through a hospital-based influenza surveillance system in South Korea from 1 November 2024, to 30 April 2025. Demographic and clinical information was collected through questionnaire surveys and electronic medical records. Influenza was diagnosed using rapid antigen tests (RATs) and reverse transcription polymerase chain reaction (RT-qPCR), and vaccine effectiveness was analyzed using multivariable logistic regression. Results: In total, 3954 participants were included, with 1977 influenza-positive cases and 1977 test-negative controls. Influenza A and B accounted for 93.1% and 7.0% of cases, respectively. The adjusted overall VE was 20.4% (95% confidence interval [CI], 8.2–30.9; p = 0.002). VE was higher in adults aged 50–64 years (46.8%) than in those aged ≥65 years (18.8%). VE was 19.9% against influenza A and 45.7% against A/H3N2. VE was higher among individuals tested using RT-qPCR than among those tested using RATs (21.5% vs. 15.7%), and was also greater during the early period than during the late period (20.5% vs. 11.4%). Vaccination did not reduce influenza-associated hospitalization risk (VE, 17.3%; 95% CI, −9.3 to 37.4). A significant reduction in hospitalization risk was observed in adults aged 50–64 years (VE, 46.8%), with no significant benefit in those aged ≥65 years. Conclusions: The 2024–2025 seasonal influenza vaccine provided moderate protection against laboratory-confirmed influenza in adults, with higher effectiveness in those aged 50–64 years. Full article

Respiratory infections are a major public health threat. Significant global mortality is caused by influenza viruses, the new SARS-CoV-2 virus, and the Respiratory Syncytial Viruses (RSVs). Wastewater-based epidemiology (WBE) has recently emerged as a valuable tool for monitoring these pathogens, providing insights into their evolution, transmission patterns, and co-circulation within populations. This study aimed to track influenza viruses (A and B), the new SARS-CoV-2 virus, and the Respiratory Syncytial Viruses (RSVs) (type A and B) during the pandemic period (from October 2020 to October 2021) in a middle-size Spanish city (Valladolid) and its surrounding areas. Viral concentration was performed using an aluminum-based precipitation method, followed by RNA extraction and RT-qPCR quantification targeting the N1 and N2 regions of the SARS-CoV-2 nucleocapsid gene, the N gene for both RSV-A and RSV-B, and the M and non-structural protein genes for influenza A and B, respectively. The results demonstrated the utility of WBE in predicting increases in clinical cases of SARS-CoV-2, as evidenced by a high correlation (r > 0.5). For RSV-A, the findings aligned with previous studies. Interestingly, particularly considering the length and period of analysis, influenza A, influenza B, and RSV-B viruses were not observed during the study period. In addition, the prevalence of RSV-A decreased during the SARS-CoV-2 pandemic, likely due to the implementation of non-pharmaceutical interventions. In conclusion, this study reaffirms that WBE provides critical epidemiological insights, complements clinical surveillance, and supports public health authorities in making informed and timely decisions. Full article

Seasonal influenza continues to pose a substantial and recurrent public health challenge in Queensland, driven by annual variability in transmission and uncertainty in climatic, demographic, and behavioural determinants. Predictive modelling is constrained by data limitations and parameter uncertainty. In response, this study developed a Bayesian network (BN) model to estimate the probability of influenza epidemics in Queensland, Australia. The model integrated diverse inputs, including international and local influenza surveillance data, demographic health statistics, and expert and stakeholder insights to capture the complex multifactorial causal relationships underlying epidemic risk. Scenario-based simulations revealed that Southeast Asian viral origin, severe global influenza seasons, peak season timing, increasing international travel, absence of control measures, and low immunisation rates substantially elevate the likelihood of influenza epidemics. Southeast Queensland was identified as particularly vulnerable under high-risk conditions. Model evaluation demonstrated good discriminative performance (AUC = 0.6974, accuracy = 70%) with appropriate uncertainty quantification through credible intervals and sensitivity analysis. Its modular design and capacity for integrating various data sources make it a practical decision-making support tool for public health preparedness and responding to evolving climatic and epidemiological conditions. Full article

Avian influenza viruses (AIVs), including H5N1 and H7N9, from the Orthomyxoviridae family present substantial public health concerns. The predominant circulating clade 2.3.4.4b has demonstrated enhanced capacity for mammalian adaptation, raising concerns about potential reassortment with human seasonal influenza viruses. Unlike H7N9’s limited host range, H5N1 infects birds, various mammals, and humans. Recent concerns include widespread H5N1 infection of U.S. dairy cattle across 18 states, affecting over 1000 herds with 71 human infections (70 H5N1 and 1 H5N5). Key observations include cow-to-cow transmission, viral presence in milk, and transmission to humans, mainly through occupational exposure. Evidence of mammal-to-mammal transmission has been documented in European and Canadian foxes and South American marine mammals. Standard pasteurization effectively inactivates the virus in milk. The continuing mammalian adaptations, particularly mutations like PB2-E627K, PB2-D701N, and PB2-M535I, suggest potential for further evolution in new hosts, emphasizing the need for enhanced surveillance to mitigate pandemic risks. Full article

Background: The COVID-19 pandemic significantly altered the circulation of respiratory viruses, including influenza. This study aimed to compare the epidemiology and clinical characteristics of paediatric influenza before, during, and after the pandemic. Methods: We retrospectively analysed 553 children aged 0–18 years hospitalised with laboratory-confirmed influenza at a paediatric infectious disease centre in Bydgoszcz, Poland, between September 2017 and August 2025. Patients were stratified into pre-pandemic (A), pandemic (B), and post-pandemic (C) periods. Epidemiological indicators, influenza type, age, sex, and hospital stay duration were assessed using χ² and non-parametric tests. Results: Hospitalisations varied across seasons, lowest in 2021/22 (n = 18) and highest in 2024/25 (n = 175). Seasonal peaks occurred January–March in groups A and C, whereas group B showed a bimodal pattern in December and March–April. Influenza type A predominated in all periods, though less during the pandemic (56.7% vs. 89.2% pre-pandemic and 73.2% post-pandemic). Median hospital stay decreased from 5 days pre-pandemic to 4 days during and after the pandemic. None of the hospitalised children were vaccinated. Conclusions: The COVID-19 pandemic influenced influenza seasonality, virus type distribution, and hospitalisation patterns in children. Observed shifts highlight the importance of ongoing surveillance and targeted vaccination strategies to mitigate influenza burden in the post-pandemic period. Full article

Background: Hospital-acquired influenza remains a persistent threat that amplifies morbidity, mortality, length of stay, and operational strain, particularly among older and immunocompromised inpatients. The COVID-19 era reshaped control norms—normalizing N95 use during surges, ventilation improvements, and routine multiplex PCR—creating an opportunity to strengthen hospital outbreak management. Methods: We conducted a targeted narrative review of WHO/CDC/Infectious Diseases Society of America (IDSA) guidance and peer-reviewed studies (January 2015–August 2025), emphasizing adult inpatient care. This narrative review synthesizes recent evidence and discusses theoretical implications for practice, rather than establishing formal guidelines. Evidence was synthesized into pragmatic practice statements on detection, diagnostics, isolation/cohorting, antivirals, chemoprophylaxis, vaccination, surveillance, and communication. Results: Early recognition and test-based confirmation are pivotal. For inpatients, nucleic-acid amplification tests are preferred; negative antigen tests warrant PCR confirmation, and lower-respiratory specimens improve yield in severe disease. A practical outbreak threshold is ≥2 epidemiologically linked, laboratory-confirmed cases within 72 h on the same ward. Effective control may require immediate isolation or cohorting with dedicated staff, strict droplet/respiratory protection, and daily active surveillance. Early oseltamivir (≤48 h from onset or on admission) reduces mortality and length of stay; short-course post-exposure prophylaxis for exposed patients or staff lowers secondary attack rates. Integrated vaccination efforts for healthcare personnel and high-risk patients reinforce workforce resilience and reduce transmission. Conclusions: A standardized, clinician-led bundle—early molecular testing, do-not-delay antivirals, decisive cohorting and Personal protective equipment (PPE), targeted chemoprophylaxis, vaccination, and disciplined communication— could help curb transmission, protect vulnerable patients and staff, and preserve capacity. Hospitals should codify COVID-era layered controls for seasonal influenza and rehearse unit-level outbreak playbooks to accelerate response and recovery. These recommendations target clinicians and infection-prevention leaders in acute-care hospitals. Full article

Influenza and other respiratory viruses pose significant public health threats among SARI patients, yet comprehensive surveillance data remain limited in Pakistan. This prospective, multi-center study characterized the burden, distribution, and molecular evolution of respiratory viruses among hospitalized SARI patients across seven tertiary hospitals from November 2022 to June 2025. Specimens were tested using RT-PCR for influenza, SARS-CoV-2, and RSV, with 375 samples sequenced via Oxford Nanopore Technology. Among 11,451 specimens, 2818 (24.6%) tested positive: RSV (1648, 14.4%), influenza (855, 7.5%; 45% H1N1pdm09, 35% H3N2, 20% influenza B), and SARS-CoV-2 (315, 2.8%). RSV predominantly affected children under 2 years (63%), while influenza and SARS-CoV-2 primarily impacted adults aged 15–40 years. Male predominance (65–79%) reflected healthcare access barriers. Strong winter seasonality (December–February) was observed for influenza and RSV. ICU admission rates were 17% for influenza, 16% for RSV, and 4% for SARS-CoV-2. Shortness of breath was associated with influenza (OR = 1.62) and RSV (OR = 1.27), while malaise (OR = 2.24) and myalgia (OR = 3.87) was associated with SARS-CoV-2. Phylogenetic analysis revealed vaccine-matched influenza clades and rapid SARS-CoV-2 variant succession (3–4 months). RSV is the primary SARI pathogen in young children, necessitating maternal vaccines and nirsevimab implementation. Sustained genomic surveillance remains essential for pandemic preparedness. Full article

Background: The Respiratory Syncytial Virus (RSV) season of 2023/2024 was conspicuously different from previous seasons, with an abrupt decrease in hospitalisation rates at the peak of the season, leading to two lower peaks instead of the expected one high peak of hospitalisations. Thus, we investigated whether there was an interference with other virus infection waves in the course of that RSV season. Methods: We analysed RSV seasons since 2016 in children who were hospitalised due to an RSV infection in Eastern Bavaria and investigated epidemiological features of RSV seasons after the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic at local, regional, and national levels. Results: Analysing patterns of four RSV seasons prior to and three seasons after the SARS-CoV-2 pandemic, we found that the paediatric RSV hospitalisation wave of the 2023/2024 season was weaker and less pronounced than expected. When we compared detailed local, regional, and national surveillance data of other viral infections, we found that paediatric RSV hospitalisation waves were anticyclical to SARS-CoV-2 infection waves, but not to rhinovirus or influenza waves in the general population. Discussion: Our data suggests that concomitant SARS-CoV-2 infection waves in the general population may disrupt infection chains of RSV in children and, thus, decrease RSV-associated hospitalisation. This factor should be taken into account when assessing the effects of the upcoming RSV prophylaxis in the future. Full article

Seasonal influenza is a major cause of morbidity and hospitalization in children, with the potential for severe complications and considerable socioeconomic impact. We conducted a retrospective observational study including 1046 children aged 0–14 years with laboratory-confirmed influenza who accessed the Paediatric Emergency Department of a tertiary center in Bologna, Italy, across three consecutive epidemic seasons (2022–2025). While the entire cohort was analysed, particular attention was given to children with severe complications requiring hospitalization, for whom more detailed clinical and laboratory data were available. Overall, 12.3% of patients required hospitalization, and 6.1% experienced complications, most frequently influenza-associated encephalopathy, lower respiratory tract infections and myositis. Influenza A predominated overall (82.0%), except for in the last season, which saw a predominance of influenza B (57.4%), closely associated with myositis and elevated creatine phosphokinase levels. Younger age was consistently associated with increased severity and hospitalization. Intensive care admissions were rare (0.8%), and no deaths were recorded. Our findings suggest that, although influenza is generally self-limiting, younger children are at higher risk of complications. These results highlight the importance of active surveillance, careful monitoring of clinical manifestations and targeted paediatric vaccination strategies to reduce the burden of seasonal influenza. Full article

Since the emergence of COVID-19, the epidemiological and seasonal patterns of respiratory pathogens have shifted, highlighting the need for ongoing surveillance. This study investigated the epidemiology, seasonal trends, and age-specific detection of respiratory viruses among patients with acute respiratory infections (ARIs) in Thailand from January to December 2024. Eight respiratory viruses were detected using multiplex real-time RT-PCR. Of 7853 samples, 60.8% (4777) tested positive. The most frequently detected pathogens were influenza virus (IFV, 24.8%), SARS-CoV-2 (21.5%), and human rhinovirus (HRV, 20.8%). IFV showed biannual peaks during the cold and rainy seasons, SARS-CoV-2 peaked in the warm months, and HRV circulated year-round. Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) were primarily detected during the rainy season (July–November), reflecting a return toward pre–COVID-19 seasonal patterns. Age-specific differences were notable: HRV was most prevalent in children < 5 years, IFV predominated among those aged 6–18 years, and adults ≥ 19 years were mainly positive for IFV and SARS-CoV-2. Co-infections were most frequent in children aged 3–5 years, often involving HRV. These findings provide updated insights into post–COVID-19 viral epidemiology, emphasize the importance of age- and season-specific surveillance, and support the development of effective public health strategies for ARI control. Full article

The epidemiology of respiratory viruses shifted considerably following the COVID-19 pandemic and the subsequent rollback of non-pharmaceutical interventions (NPIs). The initial global containment strategies implemented during the SARS-CoV-2 outbreak profoundly altered viral transmission dynamics and circulation patterns. As the World Health Organization (WHO) declared COVID-19 no longer a public health emergency in May 2023, viral circulation began reverting to pre-pandemic trends. This retrospective observational study examined the evolving epidemiological patterns of respiratory infections during and after the lifting of NPI, assessing associated clinical manifestations and their relationship with patient-specific risk factors. Data were collected from 307 patients tested between October 2021 and December 2024 using a respiratory multiplex PCR at the Rodolphe Mérieux Laboratory in Lebanon. Results revealed a reemergence of pre-pandemic seasonal trends for most viruses. Rhinovirus remained the most prevalent pathogen, likely due to the absence of a vaccine. Respiratory syncytial virus (RSV) and Influenza A resumed their characteristic winter peaks, while human metapneumovirus (HMPV) showed no co-infections, suggesting viral interference. The persistence of Influenza A and SARS-CoV-2 appeared influenced by vaccine coverage, viral mutations, and environmental factors. Multiplex PCR testing proved to be a valuable yet costly tool for both diagnosis and epidemiological surveillance. Overall, this study highlights the importance of continued viral monitoring in the post-NPI period, reflecting both the effectiveness of NPIs in limiting viral spread and the importance of ensuring wider access to advanced diagnostic methods. Full article

Background: In the post-pandemic era, respiratory viruses continue to cause substantial morbidity and mortality among hospitalized adults. SARS-CoV-2 and influenza remain the most common pathogens, while RSV and rhinovirus have re-emerged as relevant causes of severe illness. This study compared the characteristics and outcomes of virus-specific infections detected by multiplex real-time PCR over two consecutive seasons. Methods: This retrospective cohort study was conducted at a 1010-bed tertiary-care hospital in Türkiye between June 2022 and June 2024. Adults hospitalized with at least one respiratory virus detected by MRT-PCR were included. Demographic, clinical, and laboratory data were analyzed. Pathogen-specific comparisons were limited to monoinfections, and predictors of in-hospital mortality were identified using multivariable logistic regression. Results: Among 518 admissions, influenza (33.6%) and SARS-CoV-2 (29.3%) were the predominant pathogens, followed by rhinovirus (11.2%), RSV (6.6%), and other respiratory viruses (19.6%). Overall in-hospital mortality was 26.6%. Mortality differed across virus groups in unadjusted analyses, being highest in SARS-CoV-2 and RSV and lowest in rhinovirus. Non-survivors were older, more comorbid, more often immunosuppressed, and more likely to require oxygen therapy or ICU care at sampling. In multivariable analysis, independent predictors of mortality were ICU location at sampling (aOR 5.52), oxygen requirement (aOR 3.39), immunosuppression (aOR 3.67), older age (per 10-year increase: aOR 1.25), and secondary bacterial infection (aOR 7.00). Viral etiology, including SARS-CoV-2, was not independently associated with mortality after adjustment. Conclusions: Among hospitalized adults, mortality was driven primarily by host-related factors and secondary bacterial infection rather than by viral etiology. These findings highlight the need for strengthened adult immunization programs, reliable respiratory virus surveillance, the prevention of bacterial superinfection, and the development of and equitable access to effective vaccines and antiviral therapies to reduce severe outcomes in high-risk adults. Full article

Viral respiratory infections (VRIs) remain a leading cause of global morbidity and mortality. In Djibouti, diagnostic capacity for respiratory viruses is extremely limited, and little is known about the epidemiology of VRIs in the country. To address this gap, we conducted a prospective study aimed at monitoring and describing the epidemiological and virological features of VRIs over a two-year period in Djibouti. The study was carried out between January 2023 and December 2024 in seven healthcare centers. Nasopharyngeal and/or oropharyngeal swabs were collected from consenting patients presenting with influenza-like illness (ILI) or acute respiratory infections (ARI). VRIs were diagnosed using a multiplex real-time reverse transcription polymerase chain reaction (rRT-PCR) assay targeting 16 respiratory viruses. Among the 647 samples tested, at least one respiratory virus was detected in 133 (20.6%). Influenza (6.6%), rhinovirus (5.9%), and SARS-CoV-2 (3.4%) were the most frequently detected pathogens. Adult aged 26–50 years (40.8%) were the most affected, followed by those aged 15–25 years (30.4%). None of the respiratory viruses displayed a clear seasonal pattern. These findings demonstrate the co-circulation of multiple respiratory viruses among ILI/ARI patients in Djibouti and provide the first baseline data to inform national surveillance strategies. The results underscore the need to strengthen routine laboratory-based surveillance, enhance diagnostic capacity, and integrate molecular monitoring into national public health policies for better preparedness against emerging respiratory threats. Full article