WHO: Influenza Update N° 527
May 21, 2025 | Emergency Situational Updates (For reporting Week 19, ending 11 May 2025)
In the Northern hemisphere, influenza positivity continued to decline or remained stable with minor increases reported in a few countries in Central America and the Caribbean, Eastern Africa, Eastern Europe, and Southern, South-East and Eastern Asia. Influenza positivity remained elevated in Central America and the Caribbean (predominantly A(H1N1)pdm09), Eastern Africa (predominantly A viruses), Eastern Europe (predominantly B viruses), Western Asia (predominantly A(H3N2) and B viruses), Southern Asia (predominantly A(H3N2)) and Eastern and South-East Asia (predominantly A viruses). In the Southern hemisphere, positivity remained stable or increased overall. Influenza positivity was elevated in Tropical and Temperate South America (predominantly A(H1N1)pdm09), Southern Africa (predominantly A(H3N2)), Eastern Africa and South-East Asia (predominantly A viruses) and Oceania (predominantly A(H1N1)pdm09). Read More
Childhood Influenza Vaccination Is Not a Priority for Parents: A National, Cross-Sectional Survey of Barriers to Childhood Influenza Vaccination in Australia
Vaccines 2025, 13(5), 540
National data on barriers hindering paediatric influenza vaccination can inform strategies to improve uptake. The aim of this study was to measure barriers to influenza vaccination in Australian children aged <5 years. A national, cross-sectional survey of parents of children aged <5 years was conducted in March/April 2024. Parents were recruited using an online panel and asked about their intention to get an influenza vaccine for their youngest child in the upcoming influenza season. An adapted version of the validated Vaccine Barriers Assessment Tool measured 14 influenza vaccination barriers. Analysis assessed the prevalence of barriers and differences between parents intending to and those unsure or not intending to vaccinate by calculating the prevalence difference and 95% confidence interval. A total of 2000 parents were recruited nationally. The most common barrier was parents feeling distressed when thinking about vaccinating their child against influenza (66.1% of intending parents, 65.6% of unsure/not intending parents). The barrier with the largest difference between intending and not intending/unsure parents was not prioritising their child’s influenza vaccination (47.2% vs. 6.1%). Other barriers with large differences were parents not feeling guilty if their unvaccinated child got influenza (41.5% vs. 7.5) and parents not believing that influenza vaccines are effective (31.3% vs. 3.0). Parents should be encouraged and supported to prioritise influenza vaccination alongside routine childhood vaccines in campaigns that emphasise disease risk and the importance, safety and effectiveness of influenza vaccination, and by optimising access to influenza vaccination. We recommend conducting similar surveys regularly to monitor trends in parental barriers to childhood influenza vaccination. Read More
Is Influenza Vaccination Our Best ‘Shot’ at Preventing MACE? Review of Current Evidence, Underlying Mechanisms, and Future Directions
Vaccines 2025, 13(5), 522 May 14, 2025
Major adverse cardiovascular events (MACE), including myocardial infarction, stroke, and cardiovascular death, are the leading contributors to global morbidity and mortality worldwide. Accumulating evidence suggests a strong association between influenza infection and increased risk of MACE, especially in high-risk populations. Influenza vaccination has been proposed as a potential strategy for reducing this risk by mitigating systemic inflammation and preventing atherosclerotic plaque destabilization, although the precise mechanisms remain under investigation. Multiple meta-analyses and RCTs suggest that influenza vaccination is associated with a reduced risk of MACE, particularly in high-risk individuals with preexisting cardiovascular disease, but the results are less consistent for primary prevention in low-risk populations. The current data support the importance of early and annual vaccination for optimizing cardiovascular outcomes. The authors conclude that Influenza vaccination is emerging as an effective and accessible strategy to reduce the risk of major adverse cardiovascular events, particularly in high-risk individuals. While further research is needed to clarify its role in low-risk populations and the underlying mechanisms of protection, current evidence supports its integration into cardiovascular preventive care. Read More
Government livelihood project – free influenza vaccination for the older population in China: the example of Zhejiang Province
Frontiers Public Health, 19 May 2025
Influenza vaccination is an effective measure to prevent and control influenza, and countries worldwide consider older people a key recommended population for influenza vaccination. From 2020, Zhejiang Province has provided free influenza vaccination to anyone aged ≥70 years as part of its livelihood projects. In certain counties, the program is also offered to those aged ≥60 years. This measure has made influenza vaccination more convenient and has advanced the strategy for acceptance of influenza vaccines and improved readiness for a pandemic. Furthermore, it serves as an example for other Chinese provinces looking to implement free influenza vaccination programs. Match More
Broadly active intranasal influenza vaccine with a nanocomplex particulate adjuvant targeting mast cells and toll-like receptor 9
J Control Release. 2025 May 18:113855.
Flumist is the only FDA-approved intranasal influenza vaccine. Although it has recently been approved for at-home use, it has significant limitations. These include reduced effectiveness in generating a protective immune response in patients with extensive influenza exposure, safety concerns due to its live attenuated virus formulation, and reduced efficacy due to viral drift/shift. To address this limitation, we have developed a nanocomplex comprised of a mast cell (MC) agonist and toll-like receptor 9 (TLR9) ligand to adjuvant a broadly acting influenza antigen. The newly reported MC agonist was identified by screening mastoparan-7 analogs for MC degranulation activity, which led to a more active peptide analog, MP12W. Positively charged MP12W spontaneously forms nanoparticulate complexes (NPs) with CpG 1826 that were then used to intranasally vaccinate mice with a computationally optimized broadly reactive antigen (COBRA) hemagglutinin (HA) protein. The NPs were further optimized by substituting CpG 1826 with CpG 55.2, a TLR-9 agonist identified by machine learning to be more active in humans. MP12W-CpG 1826 NPs showed an increased pro-inflammatory response and decreased cytotoxicity in vitro compared to M7 complexes, translating into a safer profile in a model of increased hypersensitivity, collaborative cross mice 027 (CC027). Intranasal vaccination with this complex and broadly reactive HA resulted in higher mucosal antibody concentration and increased cytokine production with antigen recall. These responses were enhanced with MP12W-CpG 55.2 NP vaccination. MP12W-CpG NPs provided similar protection in an influenza challenge model. This study demonstrates the potential of this novel intranasal nanocomplex for vaccination. Read More
Antecedent Flu-Like Illness and Onset of Idiopathic Dilated Cardiomyopathy: The DCM Precision Medicine Study
Circulation Heart Failure. 2025 May;18(5):e012602
Previous studies have speculated that a viral infection may act as a trigger in the development of idiopathic dilated cardiomyopathy among individuals genetically at risk. In this study the authors aimed to describe the frequency of patients with DCM who reported experiencing symptoms of flu-like illness before their DCM diagnosis and to examine if this experience modified the association between genetics and DCM. The authors analyzed data from the family-based cross-sectional DCM Study conducted between 2016 and 2021. Self-reported symptoms of flu-like illness proximal to DCM diagnosis were obtained from patient interviews. Exome sequencing identified rare variants (pathogenic, likely pathogenic, or variant of uncertain significance) in DCM genes. In a case-only design, logistic mixed models were used to examine if flu-like illness modified the effect of these rare variants on DCM risk. Firth logistic regression was used to examine if flu-like illness modified the effect of each of 13 400 141 common autosomal variants (minor allele frequency ≥1%) on DCM risk. Of 1164 patients with DCM, 30.2% reported symptoms of flu-like illness proximal to DCM diagnosis. The percentage of patients with antecedent flu-like illness by variant classification was 30.0% for pathogenic/likely pathogenic, 29.6% for variant of uncertain significance only, and 30.0% for no pathogenic/likely pathogenic/variant of uncertain significance. Antecedent flu-like illness was not found to modify the effect of carrying any pathogenic, likely pathogenic, or variant of uncertain significance variants on DCM risk (interaction relative risk, 0.9). However, significant modification of the effect of rs2102158 (3q24) by antecedent flu-like illness (P=2.74×10-8) was identified by case-only genome-wide association study. Approximately one-third of patients with DCM experienced flu-like illness symptoms before DCM diagnosis. The authors did not find evidence that a flu-like illness modified the effect of rare variants on DCM risk; however, genome-wide association study analysis suggested that flu-like illness may modify the effect of a common variant on DCM risk. Read More
A protective and broadly binding antibody class engages the influenza virus hemagglutinin head at its stem interface.
mBio. 2025 May 20:e0089225.
Influenza infection and vaccination impart strain-specific immunity that protects against neither seasonal antigenic variants nor the next pandemic. However, antibodies directed to conserved sites can confer broad protection. In this study, the authors identify and characterize a class of human antibodies that engage a previously undescribed, conserved epitope on the influenza hemagglutinin (HA) protein. Prototype antibody S8V1-157 binds at the normally occluded interface between the HA head and stem. Antibodies to this HA head-stem interface epitope are non-neutralizing in vitro but protect against lethal influenza infection in mice. These antibodies bind to most influenza A subtypes and seasonal human variants, and are present at low frequencies in the memory B cell populations of multiple human donors. Vaccines designed to elicit these antibodies might contribute to “universal” influenza immunity. The authors identify a novel class of antibodies that bind most divergent HA subtypes and all seasonal human HA antigenic variants tested. These antibodies confer protection from lethal influenza challenge in animal models. The corresponding epitope on the HA head is occluded by its interaction with the stem and is inaccessible in the well-resolved prefusion state. The immunogenicity of this head-stem interface indicates that poorly understood conformations of HA presenting widely conserved surfaces are explored in biochemical, cell-based, and in vivo assays. Head-stem interface antibodies warrant further investigation as an avenue to improve influenza vaccines and therapeutics. Read More
Minimal Influenza Virus Transmission From Touching Contaminated Floors and Metal Door Levers: Laboratory Study II.
Microbiol Immunol. 2025 May 19.
Influenza is generally understood to be transmitted through inhaling virus-contaminating aerosol/droplets or contact with virus-contaminated environmental surfaces (or fomites). However, the risk associated with transmission through contact with fomites is hypothetical, lacking solid quantitative evidence. In a previous paper, the authors demonstrated through a series of experiments that the probability of influenza virus transmission from touching contaminated surfaces of face masks is minimal (Sci Rep 2024, 14, 20211). In the present study, they expanded upon this study by conducting an experimental evaluation of the likelihood of influenza transmission from dried fomites under three specific scenarios: (1) when a floor/table lies within the trajectory of artificial coughs, (2) when stainless-steel door levers are exposed to viral spraying (simulating cough), and (3) when door levers are exposed to viruses on the grasping hand. The fingertips contacting the above fomites formed on the surfaces were washed into a rinsing medium. Subsequently, they evaluated the rinsing medium for viral content using plaque-forming assay to detect the viable viruses and real-time quantitative PCR assay to detect the viral genes. The authors found that viable viruses were rarely transmitted to fingertips from the above fomites even when the viral loads in the viral fluid contaminating the fomites far exceeded that seen in real life. Consequently, we conclude that the probability of contact transmission of influenza via dried fomites is negligible or minimal under the scenarios studied here. Read More
Global distribution and health impact of infectious disease outbreaks, 1996-2023: a worldwide retrospective analysis of World Health Organization emergency event reports.
J Glob Health. 2025 May 16;15:04151.
Over 30 priority pathogens with pandemic potential were identified, underscoring the need for targeted surveillance and prevention. As infectious disease outbreaks increase globally, particularly from zoonotic and vector-borne pathogens, understanding their distribution is crucial for effective public health responses. The authors aimed to provide a comprehensive analysis of global infectious disease outbreaks from 1996-2023, addressing gaps in previous research. Data from the World Health Organization emergency events webpage, focusing on key details like disease name, location, date, and fatalities were recorded. Case fatality rates (CFR) were employed to assess outbreak severity. Outbreaks were categorised into six types – respiratory, vector-borne, foodborne/waterborne, direct contact infections, non-infectious conditions, and others. Between 1996-2023, a total of 3013 global outbreak events were reported. The Democratic Republic of the Congo had the highest frequency of outbreaks, with 272 events, followed by China with 254, and Saudi Arabia with 202. Influenza was the most frequently reported disease, with 771 outbreaks, followed by Ebola (n = 342) and Middle East respiratory syndrome-related coronavirus (MERS-CoV) (n = 305). Significant outbreaks included the 2023 global dengue outbreak, which accounted for five million cases and 5000 deaths. The CFR was highest for the Marburg virus at 76.86%, followed by haemorrhagic fever at 63.63%, and Ebola at 63.00%. The data underscore the varying severity and distribution of outbreaks, highlighting the critical need for robust global health surveillance and targeted interventions. In this study, we highlighted the significant impact of influenza, Ebola, and MERS-CoV. The high case fatality rates of viruses like Marburg and Ebola emphasised the need for early detection and rapid response systems. Strengthening global cooperation, investing in health care infrastructure, and integrating digital surveillance technologies are crucial to enhancing preparedness and reducing future outbreak impacts. Read More
Antiviral drugs for influenza reduce the duration of symptoms by up to 24 hours and do not reduce hospitalizations or deaths
Recent Prog Med 2025;116(5):322-323.
Following the widespread purchase and use of antiviral drugs during the 2009 A/H1N1 influenza pandemic, a large and heated debate has arisen within the scientific community both on their actual efficacy in the treatment of influenza and on the transparency and availability of data to inform recommendations by health institutions . Currently, the US Centers for Disease Control and Prevention (CDC) recommends administering antiviral treatment as soon as possible to patients with confirmed or suspected influenza who have severe, complicated or worsening disease and to all hospitalized patients, while in mild or low-risk cases they defer to the clinical judgment of the physician. In Europe, on the contrary, antiviral drugs for the treatment of seasonal influenza are generally under-prescribed in primary care, partly due to a lack of belief by clinicians in their efficacy, partly because in many countries these drugs are not prescribable at the expense of the National Health Services (NHS).
This network meta-analysis* was funded by the World Health Organization and conducted by a team of experienced researchers in Canada and China. The researchers searched multiple databases to identify clinical trials of influenza-specific antiviral drugs in adults and children. They identified 73 randomized trials, 19 of which were unpublished (with data drawn primarily from clinical trial registries), and the remainder published in peer-reviewed journals. Most studies involved adults and only included patients within 2 days of symptom onset. Oseltamivir had no significant effect on mortality or hospital admissions in either low- or high-risk patients. Similarly, baloxavir had no significant effect on mortality or hospital admissions in either low- or high-risk patients. The lack of benefit was seen in both patients with severe and non-severe influenza. Read More