Health system decision-makers need evidence on how modifiable factors contribute to inequalities to inform effective interventions. We examined ethnic group and deprivation inequalities in influenza and COVID-19 hospitalizations in England (2023–2024) among vaccine-eligible individuals, using causal mediation analysis to assess the roles of deprivation, vaccination uptake and comorbidities. For influenza, hospitalization odds were highest among Pakistani and Bangladeshi groups, compared with White British individuals. Deprivation mediated 26% of the total ethnic group effect for the Pakistani group and 41% for the Bangladeshi group, whilst comorbidities contributed little. Ethnic group differences in COVID-19 hospitalizations were minimal in this post-pandemic period. For both infections, the most deprived group had disproportionately high hospitalization compared to the least deprived. For influenza, vaccination uptake mediated 17%–26% of deprivation effects, whilst for COVID-19, there were no meaningful residual deprivation inequalities after including vaccination uptake and comorbidities. Vaccination uptake and deprivation mediate a substantial proportion of inequalities in hospitalization for influenza and COVID-19 in the vaccine-eligible cohort. Improving vaccination coverage in under-vaccinated groups should remain a public health priority.

The Moving Epidemic Method (MEM) is the ECDC/WHO-Europe-endorsed approach for establishing influenza epidemic thresholds and intensity levels, yet no positivity-based MEM analysis exists for Türkiye or any country in the WHO Western Asia transmission zone. Weekly influenza positivity rates from FluNet sentinel surveillance were analysed for ten of twelve seasons (2013/2014–2024/2025, excluding two COVID-19 pandemic seasons) using the mem R package with cross-validated optimized slope parameter, and Türkiye’s average epidemic curve and thresholds were compared with the Western Asia (excluding Türkiye) and South West Europe zones using Lin’s concordance correlation coefficient (CCC), root mean square deviation (RMSD) and complementary correlation metrics. The epidemic threshold was 10.59% positivity, with intensity thresholds at 42.56% (medium), 60.92% (high), and 71.38% (very high); cross-validated sensitivity was 0.77, specificity 0.88, and Matthews correlation coefficient 0.65. Türkiye’s average curve showed higher concordance with Western Asia (CCC=0.890; RMSD=4.22 percentage points) than South West Europe (CCC=0.672; RMSD=12.48) despite similar Pearson correlations (0.922 vs. 0.939), and the Western Asia epidemic threshold (11.50%) closely matched Türkiye’s. These first operational MEM thresholds for Türkiye and the first positivity-based thresholds for the Western Asia zone confirm alignment with the current WHO transmission zone classification and support integration into routine surveillance.

Evidence describing paediatric COVID-19 and influenza co-infection is limited because influenza circulation was minimal during the early COVID-19 pandemic. We used the National Clinical Cohort Collaborative, a multicentre electronic health record repository, to describe the characteristics and clinical outcomes of paediatric COVID-19 and influenza co-infections in the United States from March 2020–April 2024. We defined co-infection as COVID-19 and influenza identified <7 days apart. We reported demographics, pre-existing diagnoses, and clinical outcomes and used generalized estimating equation models. We defined clinical outcomes as Severe/Moderate disease (hospitalization, critical care, or death) versus emergency department/outpatient encounters. We repeated analyses using varying co-infection definitions to assess robustness of findings. Among 1.53 million patients, 10,277 were co-infected, and 647 (6%) were hospitalized. Co-infections occurred predominantly among children aged <12 years. The most common pre-existing diagnoses were obesity (24%), asthma (10%), and congenital/genetic conditions (5%). The risk for Severe/Moderate disease was greatest among persons aged 0–4 years (adjusted risk ratio (aRR) 3.05; 95% confidence interval (CI): 2.35–3.97) and those with ≥2 pre-existing diagnoses (aRR 2.89; 95% CI: 2.43–3.43). Similar distributions of disease severity were observed across varying co-infection definitions. This study provides a large-scale epidemiological characterization of paediatric COVID-19 and influenza co-infection and successfully implemented a practical EHR-based co-infection case definition for future analyses.

Seabirds are at high risk of extinction, and the emergence of highly pathogenic avian influenza virus (HPAIV) represents an additional threat. In 2024, HPAIV A/H5 clade 2.3.4.4b was detected for the first time in the Antarctic Continent in a dead Brown Skua (Stercorarius antarcticus), and further evidence suggests that not all species have been equally affected. We conducted a survey of HPAIV-related mortalities across 16 seabird nesting sites along the western Antarctic Peninsula (WAP) during the 2024–2025 breeding season. We report a mortality of 35 adult skuas along the WAP and beyond the Antarctic Polar Circle. Eleven skuas from six different geographic areas were sampled and all were positive to HPAIV A/H5 clade 2.3.4.4b. Phylogenetic analyses revealed that these sequences are closely related to the initial HPAIV A/H5 clade 2.3.4.4b reported in Antarctica, and post-mortem findings suggest that the viral infection was likely the cause of death. No other suspected HPAIV-related mortalities were observed in sympatric species. Our findings represent the southernmost record of skua mortality in Antarctica related to HPAIV A/H5 infection to date, demonstrating the dissemination of 2.3.4.4b clade across several localities. The virus is differentially affecting sympatric seabird species and the skuas may act as sentinel species for influenza surveillance.

The Spanish influenza pandemic of 1918 caused well over fifty million deaths. The epicentre undoubtedly was China, where gene mixing of different virus strains occurred amongst aquatic, migrant birds. But where and when did the virus first infect (or spill over to) a human being? We take, as our starting point, a paper demonstrating that an infection causing the same symptoms as the influenza virus was widespread in New York during the winter of 1917–1918. The authors of that paper went on to suggest that the virus had probably reached North America from Europe, in the context of troop movement during World War I. Our own researches have focussed on this point. We show that outbreaks of serious respiratory disease, local in nature but causing unusual patterns of mortality, were indeed reported by scientists and doctors in army hospitals in England and in France, well before the first wave of the pandemic had arrived. We use the records of these hospitals, now held in the National Archives, to trace the progress of this disease amongst the individuals who fell ill. We examine contemporary reactions to this minor epidemic – an epidemic, we suggest, which acted as a herald wave of the pandemic yet to come. The latter part of our paper addresses the second question, as to how troop movement across the North Atlantic, once the United States had entered into war, may well have enabled the virus to spread from Europe to North America.

Influenza increases the risk of secondary diseases, but other than pneumonia, many of these diseases (e.g., sinusitis, otitis media, acute myocardial infarctions) are not consistently considered in estimates of influenza burden. We used the Merative Marketscan database (2001–2019) and time-series methods to identify age-specific categories of diseases that were temporally associated with patterns of influenza activity. Next, we estimated hypothetical reductions in the incidence and costs of these diseases if influenza incidence were reduced. Of 282 different disease categories evaluated, 23 (8.2%) were strongly associated with influenza (e.g., acute bronchitis, otitis media, myocardial infarctions, sinusitis, COPD) in at least one age group. For example, we estimated a 20% decrease in peak influenza incidence could decrease acute bronchitis cases by 6.5% and pneumonia cases by 5.3%, corresponding to a $1.6 billion reduction in healthcare costs. Excluding secondary diseases associated with influenza may lead to substantial underestimates of influenza’s burden and costs.

We analysed weekly influenza A intensive care unit (ICU) or high dependency unit (HDU) admissions reported by age group and subtype by NHS trusts in England through mandatory surveillance during the 2023–2024 influenza season. We investigated whether subtype reporting varied with patient age group, NHS trust type and region. We estimated the subtype ratio and explored whether this estimate varied among subsets of trusts grouped by the regularity of subtype reporting. Our aim was to explore factors relating to subtype reporting and investigate how these affect subtype ratio estimates. 112 NHS trusts reported data, with 86 trusts reporting influenza A cases and 28 trusts reporting subtyped influenza A cases. The proportion of subtype reporting trusts varied with region and trust type, but not patient age group. The estimated ratio of influenza A(H1N1)pdm09 to influenza A(H3N2) was 3.13 (95% CI: 2.17, 4.51), indicating that influenza A(H1N1)pdm09 was dominant; this was approximately similar across levels of regularity of trust subtype reporting. The accuracy of subtype ratio estimates depends on the availability of influenza A subtype information and data representativeness. We identified low levels of subtype reporting, which likely limits early recognition of new influenza strains and informing of the prescription of antivirals in influenza outbreaks.

The activity of respiratory viruses (RVs) displays large variability in tropical regions, posing challenges for public health response strategies. Data from most RVs in south-eastern Mexico remain limited, particularly in the Yucatan Peninsula, the largest tourism hub in the country. This retrospective study analyses the regional epidemiology of RVs in Merida, the largest city in the region, using laboratory test data from a local hospital (January 2018–April 2024). Test results of 143292 RVs were collected, including 121976 for SARS-CoV-2, 19355 for influenza A and B viruses, and 1961 for 17 distinct RVs. We found that non-SARS-CoV-2 RVs circulated year-round, with higher activity in autumn and spring, while SARS-CoV-2 peaked in summer and winter. Influenza A virus, respiratory syncytial virus, and influenza B virus reached their highest activity in autumn, earlier than in other regions of Mexico. Human metapneumovirus peaked during autumn-winter. Rhinovirus/enterovirus and parainfluenza showed year-round activity, with peaks in autumn and spring. Other coronaviruses were more frequent during winter-spring. In post-pandemic years (2022–2023), adenovirus outbreaks emerged, as well as an increased prevalence of non-SARS-CoV-2 RV co-infections. This study highlights the need for region-specific public health strategies, including optimized vaccination schedules, such as for influenza A virus, and enhanced diagnostic surveillance.

Measuring waning in vaccine effectiveness (VE) is challenging due to potential depletion-of-susceptibles bias. Some SARS-CoV-2 studies excluded individuals with prior infection and adjusted for the probability of remaining uninfected. We applied this approach to assess waning influenza VE in Hong Kong during the 2012/2013 season. First, we estimated the infection risk for unvaccinated children using published serological and surveillance data. Next, we derived infection risk for vaccinated children, assuming VE against infection of 57%. Uncorrected VE from 14 to 270 days post-vaccination was estimated from hospitalized children. We calculated the rate of depletion of susceptibles given infection risk and VE corrected for depletion-of-susceptibles bias. Waning rates for uncorrected and bias-corrected VE were measured by comparing VE at day 270 versus day 14. Bias was assessed as the absolute difference between two waning rates in percentage points. Waning rate of uncorrected VE was overestimated by 5.9 percentage points or 1.3 percentage points when assessed up to day 120. Bias was substantial when assuming 80% unvaccinated, and all vaccinated children were initially uninfected, but minimal when these proportions were similar. The observed waning in 2012/2013 was unlikely due to depletion-of-susceptibles bias. Further studies across various conditions are needed to confirm our findings.

This article examines the relationship between primary care (PC) settings and the uptake of COVID-19 and influenza vaccines in 29 European countries. Using multiple linear regression, the study evaluates whether PC settings influence vaccine uptake (VU) for these two vaccines. Based on secondary data, the study shows that people behave differently in the context of COVID-19 and influenza vaccination. Our findings suggest that health systems relied less on PC during the pandemic, not fully using its potential for COVID-19 vaccination. Even if the bivariate correlations highlight the importance of PC, the regression analysis did not verify a direct relation between PC strength and the COVID-19 VU. In contrast, for influenza vaccination, PC strength was the only significant variable. The core research message is that systematic comparative evidence regarding the relation between PC and VU is needed. Based on the belief that appropriate PC setting and adequate general practitioners (GP) involvement in vaccination could contribute to higher VU, the main policy implication of the research is that more attention needs to be paid to PC setting and the role of GPs in vaccination policy.

This study examined global trends in influenza-associated lower respiratory infections (LRIs) deaths from 1990 to 2019 using data from the GBD 2019. The annual percentage change (APC) and average annual percentage change (AAPC) were used to analyze age-standardized death rates (ASDR). Globally, the ASDR of influenza-associated LRIs was 3.29/100,000 in 2019, which was higher in the African region (6.57/100,000) and among adults aged 70 years and older (29.88/100,000). The ASDR of influenza-associated LRIs decreased significantly from 1990 to 2019 (AAPC = −1.88%, P < 0.05). However, it was significantly increased among adults aged 70 years and older during 2017–2019 (APC = 2.31%, P < 0.05), especially in Western Pacific Region and South-East Asia Regions. The ratio of death rates between adults aged 70 years and older and children aged under 5 years increased globally from 1.63 in 1990 to 5.34 in 2019, and the Western Pacific Region experienced the most substantial increase, with the ratio soaring from 1.83 in 1990 to 12.98 in 2019. Despite a decline in the global ASDR of influenza-associated LRIs, it continues to impose a significant burden, particularly in the African, Western Pacific regions and among the elderly population.

The H3N2 canine influenza virus (CIV) emerged from an avian reservoir in Asia to circulate entirely among dogs for the last 20 years. The virus was first seen circulating outside Asian dog populations in 2015, in North America. Utilizing viral genomic data in addition to clinical reports and diagnostic testing data, we provide an updated analysis of the evolution and epidemiology of the virus in its canine host. CIV in dogs in North America is marked by a complex life history – including local outbreaks, regional lineage die-outs, and repeated reintroductions of the virus (with diverse genotypes) from different regions of Asia. Phylogenetic and Bayesian analysis reveal multiple CIV clades, and viruses from China have seeded recent North American outbreaks, with 2 or 3 introductions in the past 3 years. Genomic epidemiology confirms that within North America the virus spreads very rapidly among dogs in kennels and shelters in different regions – but then dies out locally. The overall epidemic therefore requires longer-distance dispersal of virus to maintain outbreaks over the long term. With a constant evolutionary rate over 20 years, CIV still appears best adapted to transmission in dense populations and has not gained properties for prolonged circulation among dogs.

The epidemiology of respiratory infections may vary depending on factors such as climate changes, geographical features, and urbanization. Pandemics also change the epidemiological characteristics of not only the relevant infectious agent itself but also other infectious agents. This study aims to assess the impact of the COVID-19 pandemic on the epidemiology of viral respiratory infections in children. We retrospectively reviewed the medical records of children aged ≤18 years with laboratory-confirmed viral respiratory infections other than COVID-19 from January 2018 to March 2023. Data on demographic characteristics, month and year of admission, and microbiological results were collected. During the study period, 1,829 respiratory samples were sent for polymerase chain reaction testing. Rhinovirus was identified in 24% of the patients, mixed infections in 21%, influenza virus in 20%, and respiratory syncytial virus in 12.5%. A 38.6% decrease in viral respiratory infections was observed in 2020, followed by a 188% increase in 2021. The respiratory syncytial virus was significantly more common in the post-pandemic period (13.8%) compared to the pre-pandemic period (8.1%), but no seasonal shift in respiratory syncytial virus infection was observed. There was also a yearly increase in influenza infections in the post-pandemic period compared to the pre-pandemic period. After the COVID-19 pandemic, the frequency of parainfluenza virus infections increased during the summer months, and this finding provides a new contribution to the existing literature.

Seasonal influenza epidemics result in high levels of healthcare utilization. Vaccination is an effective strategy to reduce the influenza-related burden of disease. However, reporting vaccine effectiveness does not convey the population impacts of influenza vaccination. We aimed to calculate the burden of influenza-related hospitalizations and emergency department (ED) attendance averted by influenza vaccination in Victoria, Australia, from 2017 to 2019, and associated economic savings. We applied a compartmental model to hospitalizations and ED attendances with influenza-specific, and pneumonia and influenza (P&I) with the International Classification of Diseases, 10th Revision, Australian Modification (ICD-10-AM) diagnostic codes of J09-J11 and J09-J18, respectively. We estimated an annual average of 7657 (120 per 100000 population) hospitalizations and 20560 (322 per 100000 population) ED attendances over the study period, associated with A$85 million hospital expenditure. We estimated that influenza vaccination averted an annual average of 1182 [range: 556 – 2277] hospitalizations and 3286 [range: 1554 – 6257] ED attendances and reduced the demand for healthcare services at the influenza season peak. This equated to approximately A13 [range: A6 – A25] million of savings over the study period. Calculating the burden averted is feasible in Australia and auseful approach to demonstrate the health and economic benefits of influenza vaccination.

Influenza and other acute respiratory viral infections (ARVIs) are among the most common human diseases. In recent decades, the discovery of cytokines and their significance in the pathogenesis of diseases has led to extensive research on these compounds in various pathologies including ARVIs. The aim of the research was to study the cytokine profile in patients with ARVIs. The cases of 30 patients were investigated. Etiological diagnosis was performed by polymerase chain reaction. Different classes of cytokines in the serum were defined by the enzyme-linked immunosorbent assay (ELISA). The level of cytokines depended on the number of pathogens. The highest levels of pro-inflammatory interleukins and the lowest levels of anti-inflammatory IL-4 were observed in patients with a combination of five or more viruses compared to those with a monoinfection. Analysis of the data showed that in the acute phase, the levels of all studied pro-inflammatory cytokines – IL-2, IL-6, and TNF-α – increased by 8, 39, and 9 times, respectively, compared to those in healthy individuals. In the acute phase of ARVI, the levels of pro-inflammatory cytokines were significantly higher and depended on the severity of the disease. The imbalance of cytokines in the serum has been established in cases of ARVIs, depending on the severity of the disease.