Random Forest of epidemiological models for Influenza forecasting.

Preexisting Immunity to Pandemic (H1N1) 2009

Influenza-Associated Cystic Fibrosis Pulmonary Exacerbations

Decreased influenza activity during the COVID-19 pandemic-United States, Australia, Chile, and South Africa, 2020.

Influenza Virus Receptor Specificity: Disease and Transmission

Clinical Management of Pandemic 2009 Influenza A(H1N1) Infection

Human Infection with Eurasian Avian-like Influenza A(H1N1) Virus, China

Background Highly pathogenic avian influenza A(H5) viruses pose a pandemic threat, with a history of zoonotic spillovers into humans that are presumed immunologically naïve. Whether the general population is currently immunologically naïve to circulating A(H5) influenza viruses is unknown. Methods To evaluate the presence of cross-reactive immune responses to emerging A(H5) clade 2.3.4.4b influenza viruses in the general population, we conducted comprehensive immune profiling on cross-sectional samples from healthcare workers (n=107). Samples were collected in August and September 2024 in the scope of an ongoing prospective follow-up study: ‘Surveillance of rEspiratory viruses iN healThcare and anImal workers in the NethErLands’ (SENTINEL). Findings Low-level antibody responses directed against the A(H5) hemagglutinin (HA) head were detected in a limited number of individuals, but without hemagglutination inhibition activity. Nevertheless, we detected in most participants A(H5)-reactive antibodies with Fc-effector functions, likely directed at the conserved HA stalk. Additionally, we observed abundant neuraminidase (NA) inhibiting antibodies against avian N1s and T-cell responses against HAs and NAs from A(H5) influenza viruses. These responses correlated strongly with immune responses targeting an A(H1N1) seasonal influenza virus, indicating they were likely induced by prior exposures. Interpretation Together, our findings suggest that partial cross-reactive immunity to A(H5) influenza viruses exists in humans, which may play an important role during future outbreaks, potentially by blunting disease severity. Characterizing such baseline immunity is crucial for accurate pandemic risk assessment and preparedness planning. Funding Netherlands Organization for Health Research and Development (ZonMw), European Union’s EU4Health program DURABLE, Dutch Ministries of Agriculture, Fisheries, Food Security and Nature and Health, Welfare and Sport, National Institute of Health - National Institute of Allergies and Infectious Diseases (NIH-NIAID). The funding sources had no role in study design, data collection, analysis, interpretation of the data, or the decision to submit the paper for publication. Research in context Evidence before this study We searched PubMed (Jan 1997 – Jul 2025; English) using “influenza”, “heterosubtypic”, “immunity”, “cross-immunity”, “baseline”, “population”, “H5N1”, “avian influenza”, “clade 2.3.4.4b”, “humoral”, “antibodies”, “cellular”, “T-cells”, and relevant combinations. Prior work to assess population immunity to A(H5) influenza viruses is fragmented: most reports measured binding antibodies, hemagglutination inhibition (HI) antibodies, or neutralizing antibodies exclusively, and few examined T-cell responses. The measurement of integrated antibody breadth, functional HI, neuraminidase inhibition (NI), and antibody-dependent cellular cytotoxicity (ADCC) activity, as well as T-cell responses, has not been described in cross-sectional population studies. Added value of this study We present profiling of immunity to A(H5) influenza viruses in an inferred unexposed cross-sectional sample of healthcare workers (n=107). This comprehensive analysis revealed patterns that were not detected in earlier single-endpoint studies: (i) A(H5) binding antibodies mainly targeted the conserved stalk, with higher titers in adults over 60 years, (ii) A(H5)-reactive NI-and ADCC-mediating antibodies were common, and (iii) cross-reactive T-cell responses against HAs and NAs of A(H5) influenza viruses were detected. The rational selection of antigens from both seasonal and avian influenza viruses allowed for direct comparison of multiple effector mechanisms. These design choices led to the first comprehensive map of humoral and T-cell effector functions against A(H5) influenza viruses, establishing a robust baseline for future vaccine evaluations and pandemic-risk assessments. Implications of all the available evidence Our findings in combination with existing research shows that that immunity to A(H5) influenza viruses is widespread. It is likely that repeated exposure to seasonal influenza viruses led to the development of a cross-reactive antibody and T-cell repertoire capable of recognizing emerging A(H5) influenza viruses. While the protective value of the cross-reactive immune responses remains speculative, evidence from model systems suggests these could confer protection, potentially blunting disease severity in the case of a future outbreak.

Seasonal human influenza virus continues to cause morbidity and mortality annually, and highly pathogenic avian influenza (HPAI) viruses along with other emerging influenza viruses continue to pose pandemic threats. Vaccination is considered the most effective measure for controlling influenza; however, current strategies rely on a precise vaccine match with currently circulating virus strains for efficacy, requiring constant surveillance and regular development of matched vaccines. Current vaccines focus on eliciting specific antibody responses against the hemagglutinin (HA) surface glycoprotein; however, the diversity of HAs across species and antigenic drift of circulating strains enable the evasion of virus-inhibiting antibody responses, resulting in vaccine failure. The neuraminidase (NA) surface glycoprotein, while diverse, has a conserved enzymatic site and presents an appealing target for priming broadly effective antibody responses. Here we show that vaccination with parainfluenza virus 5 (PIV5), a promising live viral vector expressing NA from avian (H5N1) or pandemic (H1N1) influenza virus, elicited NA-specific antibody and T cell responses, which conferred protection against homologous and heterologous influenza virus challenges. Vaccination with PIV5-N1 NA provided cross-protection against challenge with a heterosubtypic (H3N2) virus. Experiments using antibody transfer indicate that antibodies to NA have an important role in protection. These findings indicate that PIV5 expressing NA may be effective as a broadly protective vaccine against seasonal influenza and emerging pandemic threats.IMPORTANCE Seasonal influenza viruses cause considerable morbidity and mortality annually, while emerging viruses pose potential pandemic threats. Currently licensed influenza virus vaccines rely on the antigenic match of hemagglutinin (HA) for vaccine strain selection, and most vaccines rely on HA inhibition titers to determine efficacy, despite the growing awareness of the contribution of neuraminidase (NA) to influenza virus vaccine efficacy. Although NA is immunologically subdominant to HA, and clinical studies have shown variable NA responses to vaccination, in this study, we show that vaccination with a parainfluenza virus 5 recombinant vaccine candidate expressing NA (PIV5-NA) from a pandemic influenza (pdmH1N1) virus or highly pathogenic avian influenza (H5N1) virus elicits robust, cross-reactive protection from influenza virus infection in two animal models. New vaccination strategies incorporating NA, including PIV5-NA, could improve seasonal influenza virus vaccine efficacy and provide protection against emerging influenza viruses.

The 2009 H1N1 Pandemic Adds to Our Knowledge of Influenza Pathogenesis

Please cite this paper as: Koul PA., et al. (2011) Pandemic and seasonal influenza viruses among patients with acute respiratory illness in Kashmir (India). Influenza and Other Respiratory Viruses 5(6), e521–e527.Background With the emergence of pandemic influenza A (2009A/H1N1) virus in India, we sought to determine the prevalence and clinical presentations of seasonal and pandemic influenza viruses among acute respiratory illness (ARI) patients from Srinagar, a temperate climate area in northern India, during the peak winter season.Methods Combined throat and nasal swabs, obtained from 194 (108 male) presenting with ARI from January to March 2010 (Week 53‐week 10), were tested by RT‐PCR for influenza A and B, including 2009A/H1N1 viruses. HA1 gene of selected 2009A/H1N1‐positive samples was sequenced, and phylogenetic analysis was carried out.Results Twenty‐one (10·8%, age 15–80 years, median age 40 years) patients tested positive for influenza viruses: 13 (62%) for 2009A/H1N1 virus, 6 (28·5%) for seasonal influenza A (H3N2), and 2 (9·5%) for influenza B. Twelve of the 13 patients with 2009A/H1N1 presented with febrile ARI, and eight had associated comorbidities. All of the patients recovered. Phylogenetic analysis of HA gene (n = 8) revealed that all strains from Srinagar clustered in 2009A/H1N1 clade seven along with the other 2009A/H1N1 strains from India. Amino acid substitutions in the HA protein defining clade seven (P83S, S203T, and I321V) were found in almost all isolates from Srinagar.Conclusions Both seasonal and 2009A/H1N1 viruses appear to be associated with ARI in Srinagar. The 2009A/H1N1 in Srinagar is genetically similar to globally circulating clade 7 strains, with unique signature sequences in the HA gene. Further investigations into ascertain the role of these mutations in possible alteration of the virulence and transmissibility of the virus are needed.

It was shown previously that human saliva has higher antiviral activity against human influenza viruses than against H5N1 highly pathogenic avian influenza viruses, and that the major anti-influenza activity was associated with sialic-acid-containing molecules. To further characterize the differential susceptibility to saliva among influenza viruses, seasonal influenza A and B virus, pandemic H1N1 virus, and 15 subtypes of avian influenza virus were tested for their susceptibility to human and chicken saliva. Human saliva showed higher hemagglutination inhibition (HI) and neutralization (NT) titers against seasonal influenza A virus and the pandemic H1N1 viruses than against influenza B virus and most avian influenza viruses, except for H9N2 and H12N9 avian influenza viruses, which showed high HI and NT titers. To understand the nature of sialic-acid-containing anti-influenza factors in human saliva, α2,3- and α2,6-linked sialic acid was measured in human saliva samples using a lectin binding and dot blot assay. α2,6-linked sialic acid was found to be more abundant than α2,3-linked sialic acid, and a seasonal H1N1 influenza virus bound more efficiently to human saliva than an H5N1 virus in a dot blot analysis. These data indicated that human saliva contains the sialic acid type corresponding to the binding preference of seasonal influenza viruses.

Objective To investigate the prevalence of influenza virus infections in infants and young children during the pandemic period of 2009 influenza A(H1N1)in Beijing.Methods Throat swabs were collected from children visited the affiliated Children's Hospital to Capital Institute of Pediatrics for influenza-like illness from June 1,2009 to February 28,2010.The specific gene segments of 2009 pandemic influenza H1N1 and seasonal influenza viruses were amplified from samples by real-time RT-PCR recommended by WHO and National Influenza Reference Center of China.Results Out of 4363 clinical samples tested by real-time RT-PCR,the total positive rate of influenza A viruses was 29.3%,including 623(14.3%)identified as 2009 pandemic influenza A(H1N1)and 657(15.1%)influenza A viruses without subtype identity.Among those pandemic influenza H1N1 positive,23 were severe cases with 5 deaths.The ages for 618 pandemic influenza H1N1 infected children with completed information were from 14 days to 16 years.The ratio of male to female wag 1.3:1.Among them,25.2% were patients in age group of 1 to 3 years old and distribution of children in age groups of 3 to 6 years old and 6 to 12 years old were similar(about 30.0%).During the survey period,it appeared only one prevalence wave of pandemic influenza H1N1.The positive rate of pandemic H1N1 increased in September and the peak(36.5%of positive rate)was in November and then declined to 2.7%in February 2010.The data from routine influenza virus surveillance from 20-30 clinical samples collected each week indicated an alternative prevalence of seasonal H3N2,pandemic H1N1 and influenza B during this study period.Respiratory syncytial virus(RSV)became predominant in children after the circulating of pandemic H1N1.Conclusion There was an epidemic of pandemic influenza H1N1 in children in Beijing from June 2009 to February 2010,especially in those of preschool and school aged children.Seasonal influenza viruses and pandemic influenza H1N1 were contributed alternatively. Key words: 2009 pandemic influenza H1N1; Seasonal influenza; Children

Technical guidelines for seasonal influenza vaccination in China (2022-2023)

Technical guidelines for seasonal influenza vaccination in China (2022-2023)

BackgroundThis population study aimed to investigate influenza and influenza-like respiratory virus infections in children during the 2019/20 influenza season and the coronavirus disease 2019 (COVID-19) pandemic in Poland.Material/MethodsThis study analyzed data from the National Influenza Centre, the Department of Influenza Research at the National Institute of Public Health, and 16 Voivodeship Sanitary and Epidemiological Stations in Poland. Nose and throat swabs were obtained from children during the 2019/20 influenza season and the COVID-19 pandemic. Viral RNA detection was performed using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to diagnose influenza virus infection and viral subtypes.ResultsIn the analyzed group, both cases of influenza A and B and infections with influenza-like viruses were confirmed. Among all cases caused by influenza viruses, influenza A was more frequent than B, with predominance of the A/H1N1/pdm09 subtype. The flu-like virus which infected most children was the human respiratory syncytial virus (RSV). The greatest number of cases with RSV was registered in the group of the youngest children (0–4 years).ConclusionsThis population study from Poland showed that during the COVID-19 pandemic, and during the winter influenza season of 2019/20, influenza and influenza-like viral infections in children showed some differences from previous influenza seasons. The findings highlight the importance of viral infection surveillance and influenza vaccination in the pediatric population.