Pregnant women and infants <6 months are at increased risk of influenza-associated complications. Maternal influenza vaccination during pregnancy has a strong safety record and is effective in reducing the risk of illness in these groups. Here, we estimate influenza disease burden, and the burden prevented by maternal influenza vaccination, among pregnant women and their infants <6 months in the United States during the 2011/12-2019/20 influenza seasons. We applied a multiplier model and compartmental framework to data that included monthly influenza-associated hospitalizations among pregnant women and infants <6 months, influenza vaccination coverage among pregnant women, and influenza vaccine effectiveness. We estimated the number of influenza-associated hospitalizations and intensive care unit (ICU) admissions among pregnant women and infants <6 months, and the corresponding number prevented by vaccination. We also simulated alternative vaccination coverage scenarios to investigate whether increased and/or earlier influenza vaccination uptake each season could have prevented additional hospitalizations. From 2011/12 to 2019/20, we estimated that 2670-10,000 influenza-associated hospitalizations and 76-486 ICU admissions occurred annually among pregnant women, and 3960-13,100 hospitalizations and 457-1830 ICU admissions occurred annually among infants <6 months. Influenza vaccination prevented an estimated 33-2440 hospitalizations and 1-166 ICU admissions annually among pregnant women, and 29-1350 hospitalizations and 4-178 ICU admissions annually among infants <6 months. We projected that increased influenza vaccination uptake would have prevented more hospitalizations among pregnant women than earlier vaccination, whereas the converse was true for infants <6 months. Together, we estimated increased and earlier vaccination uptake could have prevented an additional 12-942 influenza-associated hospitalizations annually among pregnant women and 17-1010 hospitalizations annually among infants <6 months. Our findings suggest maternal influenza vaccination reduces disease burden among pregnant women and their infants <6 months who are too young to be vaccinated.

Background:Real-world evidence on antiviral dispensing for influenza outpatients with underlying medical conditions (UMCs) is limited. We characterized dispensing among influenza outpatients aged <65 years with UMCs, comparing commercial and Medicaid coverage. Methods:We used outpatient encounter claims from the US MarketScan Commercial and Medicaid databases during October-April of the 2018-2019 through 2023-2024 influenza seasons and October-December 2024-2025. Eligible encounters included patients aged <65 years with a clinical influenza diagnosis, ≥1 UMC, and ≥12 months of continuous enrollment before diagnosis. Antiviral treatment was defined as dispensing of oseltamivir, peramivir, zanamivir, or baloxavir within 7 days of the encounter. We described demographic, clinical, and care-seeking characteristics and evaluated overall and same-day dispensing by insurance type. Results:Among 549 424 encounters, 268 463 (48.9%) were commercially insured (median age 19 years [interquartile range, IQR, 8-44]) and 280 961 (51.1%) were Medicaid insured (median age 10 years [IQR 5-18]). Chronic pulmonary disease was the most common UMC (88.0% and 81.8%). Antivirals were dispensed in 54.2% (commercial) and 53.7% (Medicaid) of encounters, almost exclusively oseltamivir. Same-day dispensing occurred in 91.1% of commercial and 81.4% of Medicaid encounters. Overall dispensing was lowest among patients with emergency department encounters or multiple outpatient visits; same-day dispensing was lowest among those with multiple UMCs, emergency department encounters, or multiple visits. Dispensing increased with age in commercial encounters but declined among adults with Medicaid. Conclusions:About half of higher-risk influenza outpatients received antivirals. Overall dispensing was similar by insurance type, but Medicaid patients and those with multiple UMCs had greater delays.

Emergency department (ED) visits during influenza seasons represent a critical yet less examined indicator of the acute burden of influenza. This study investigates the burden of influenza-associated ED visits in 6 US cities during influenza seasons from 2005-2006 to 2016-2017. Using a time-series design, we estimated associations between daily ED visits and weekly influenza activity data from the Influenza Hospitalization Surveillance Network (FluSurv-NET). A counterfactual approach was then used to calculate attributable expected ED visits. Highest influenza-associated rates were observed among the youngest (0-4 years) and oldest (65+ years) age groups. Combining estimates across seasons, the influenza-associated ED visit rate for respiratory diseases was almost 6 times larger compared to the subset of ED visits that resulted in hospitalization: 364 per 100 000 population (95% CI, 294-435) for total ED visits vs 58 per 100 000 population (95% CI, 45-71) for hospitalization. This difference was particularly large for the 0-4 years age group: 911 per 100 000 population (95% CI, 558-1263) for total ED visits vs 43 per 100 000 population (95% CI, 15-71) for hospitalization. This study highlights the substantial burden of influenza on emergency health care services and the importance of integrating such data into public health planning and influenza management strategies.

Importance:Antigenically drifted influenza A(H3N2) J.2.4.1 (subclade K) viruses predominated during the 2025-2026 Northern Hemisphere influenza season. Objective:To describe influenza activity and burden, characterize subclade K, evaluate susceptibility to influenza antivirals and postinfluenza vaccination antibodies, and estimate vaccine effectiveness. Design, Setting, and Participants:This surveillance study used multiple data sources, including (1) national surveillance of influenza-positive respiratory specimens collected by approximately 300 clinical laboratories and 100 public health laboratories from October 1, 2025, through March 14, 2026, a subset of which were further characterized; (2) serologic data of people who received 2025-2026 influenza vaccines; (3) influenza admissions data from the Influenza Hospitalization Surveillance Network (ie, 10% of US population) and the associated estimates of US burden; and (4) test-negative, case-control vaccine effectiveness estimates from the Virtual SARS-CoV-2, Influenza, and Other Respiratory Viruses Network. Exposures:Influenza infection, hospitalization, and vaccination. Main Outcomes and Measures:Outcomes included influenza virus type, subtype, and clade; antiviral susceptibility; immunogenicity; influenza-associated outpatient and emergency department visits, hospitalizations, and mortality; estimated influenza illnesses, hospitalizations, and death; and estimated vaccine effectiveness. Results:As of March 14, 2026, of the 55 318 influenza-positive respiratory specimens tested by public health laboratories, most (50 291 specimens [90.9%]) were influenza A, of which 40 779 (81.1%) were subtyped and 35 801 (87.8%) were A(H3N2). Of the 1754 characterized A(H3N2) viruses, most (1626 specimens [92.7%]) were subclade K. Postinfluenza vaccination neutralizing geometric mean antibody titers against subclade K were reduced 1.62 (95% CI, 1.29-2.02)-fold compared with the vaccine virus. All 1729 tested A(H3N2) viruses were sensitive to antivirals. Of the 27 881 recorded influenza hospitalizations, 15 426 (54.7%) were among female patients, and 15 051 (54.0%) were among patients aged 65 years or older. The estimated cumulative influenza-associated hospitalization rate was 80.0 per 100 000 which would correlate with estimates of between 28 000 000 to 49 000 000 illnesses, 360 000 to 740 000 hospitalizations, and 22 000 to 74 000 deaths in the US during the 2025-2026 season. Adjusted interim vaccine effectiveness estimates against influenza-associated emergency department or urgent care encounters and hospitalizations were 35% (95% CI, 33%-38%) and 27% (95% CI, 21%-34%), respectively. Conclusions and Relevance:This surveillance study found that while antigenically drifted viruses predominated and caused substantial morbidity and mortality, influenza vaccines were associated with a reduced risk of influenza among those who were vaccinated, and recommended antivirals remained effective.

Many U.S. households keep backyard bird flocks for their personal food supply or as garden partners. Backyard flocks in the United States have occasionally been infected with avian influenza A viruses, putting flock owners at risk for exposure. During July-December 2025, CDC, in collaboration with state health and agricultural partners, conducted an online survey to learn more about backyard flock owners and their knowledge, attitudes, and practices related to avian influenza. Among 638 respondents who completed the survey, 92% were White (and not Hispanic or Latino), and approximately one half had a graduate or professional degree; a majority kept small, predominantly chicken flocks; and many reported that wild birds could access their flock or the flock's food or water, which increases the flock's risk for avian influenza exposure. Although a majority of respondents had heard of avian influenza, approximately one third were unaware of the signs and symptoms of infection in their birds or humans. If they needed to interact with ill or dead birds, a majority of owners knew the recommended precautions to take and indicated willingness to use most, though not all, recommended personal protective equipment. These findings highlight important topics for risk messaging and educational resources so that backyard flock owners are better informed and better able to protect their flocks, themselves, and their families from avian influenza.

BACKGROUND:Older individuals (≥65 years) are at greatest risk of severe influenza requiring hospitalization. Since 2009, influenza-associated hospitalization rates during A(H1N1)pdm09-predominant influenza seasons have been lower than during A(H3N2) -predominant seasons. \. METHODS:Using laboratory-confirmed influenza hospitalization rates from U.S. population-based surveillance, we investigated the relative A(H1N1)pdm09 to A(H3N2) hospitalization rate ratios by patient year of age and birth cohort from 2010 through 2025. RESULTS:Results suggest partial protection against A(H1N1)pdm09 hospitalizations relative to A(H3N2) hospitalizations among patients born before 1945 (pre-1945 birth cohorts), and among individuals born during 1994 through 2009. Impact of partial protection against A(H1N1)pdm09-associated hospitalizations has diminished over time among older adults, contributing to elevated influenza hospitalization rates during the 2024-2025 influenza season. CONCLUSIONS:Our findings suggest that influenza A hospitalization rates may increase during future influenza seasons when both influenza A(H3N2) and A(H1N1) viruses circulate or following the emergence of novel A(H1N1)pdm09-like viruses.

Abstract Since the U.S. 2013/14 influenza season, the CDC’s FluSight Challenge has provided a platform for evaluating influenza forecasting models and fostering collaboration across institutions. The Challenge aims to improve the science and enhance the utility of infectious disease forecasts for public health decision making. We analyzed ten years of submitted forecasts (2014/15-2019/20 (influenza-like illness seasons) and 2021/22-2024/25 (hospital admissions seasons)) across a range of model types, including statistical, mechanistic, machine learning, and hybrid models. Influenza-like illness (ILI) forecasts were evaluated using the exponentiated logarithmic score (skill metric) while hospital admissions forecasts were evaluated using the log transformed relative Weighted Interval Score. Corresponding potential performance differences were assessed using Wilcoxon rank-sum tests, and associations with team participation history were evaluated using Spearman’s rank correlation. Model performance varied by season, and no single model type consistently outperformed others. In ILI seasons, statistical models generally performed better than mechanistic and machine learning models, though consistent differences were not observed in more recent hospital admissions seasons. Ensemble forecasts showed better overall performance across seasons, and the CDC’s FluSight ensemble ranked among the top-performing forecasts every year. We also found a positive correlation between forecast accuracy and the number of years a team participated in the Challenge, with statistically significant associations in four seasons. These findings highlight the benefits of ensemble approaches and sustained engagement in improving forecasting performance, while also underscoring the continued value of forecast evaluation before and following the COVID-19 pandemic. Insights from the FluSight Challenge can guide future infectious disease forecasting efforts and support more effective public health preparedness.

With declining influenza vaccine coverage since the coronavirus disease (COVID-19) pandemic, it is more critical than ever to provide a strong evidence base to support the benefits of influenza vaccination. Influenza vaccination can reduce the risk of influenza-associated outpatient visits and hospitalizations, and some studies have also shown that influenza vaccination can decrease the severity of disease among those who develop influenza illness despite vaccination. Yet, using observational real-world data to demonstrate these benefits is challenging. In this commentary, we outline some of the challenges and issues to consider when designing observational studies to demonstrate the benefits of influenza vaccination among patients hospitalized with influenza. We further provide suggestions for how to create more standardized definitions for severe and critical influenza outcomes against which vaccine benefits may be measured, using lessons learned from the COVID-19 pandemic.

Importance:Since 2020, COVID-19 has dramatically impacted the US population and health care system. Reporting requirements, circulating variants, testing practices, and population immunity from vaccination and previous infections evolved as the COVID-19 pandemic progressed. Evidence-based public health policy and resource allocation decisions require current estimates of disease burden. Objective:To estimate the age group-specific burden of COVID-19-associated illnesses, outpatient visits, hospitalizations, and deaths in the US from October 2022 to September 2024. Design, Setting, and Participants:In this cross-sectional study, hierarchical Bayesian modeling, adjusting for underdetection of SARS-CoV-2 due to testing practices and test sensitivity, was applied to hospitalization data from the population-based COVID-19 Hospitalization Surveillance Network (COVID-NET) database, which includes 89 counties and jurisdictional equivalents in 12 states covering approximately 10% of the US population. Data from 94 363 participants from October 2022 to September 2023 (surveillance period, 2022-2023) and from 72 176 participants from October 2023 to September 2024 (surveillance period, 2023-2024) were included, and probabilistic mathematical multiplier models estimated counts of deaths, outpatient visits, and symptomatic illnesses incorporating literature and study-based multipliers. Data were modeled from April 2024 to September 2025. Exposures:COVID-NET patients with a laboratory-confirmed COVID-19-associated hospitalization, defined as a positive SARS-CoV-2 test result within 14 days before or during hospitalization. Main Outcomes and Measures:Estimated national counts with 95% uncertainty intervals (UIs) of outpatient visits, illnesses, hospitalizations, and deaths by age group. Results:In 2022-2023, there were an estimated 43.6 million (95% UI, 25.3-64.0 million) COVID-19-associated illnesses, 10.0 million (95% UI, 7.0-13.1 million) outpatient visits, 1.1 million (95% UI, 0.9-1.4 million) hospitalizations, and 101 300 (95% UI, 73 600-132 500) deaths. In 2023-2024, there were an estimated 33.0 million (95% UI, 20.2-49.0 million) COVID-19-associated illnesses, 7.7 million (95% UI, 5.5-9.9 million) outpatient visits, 879 100 (95% UI, 738 600-1 039 000) hospitalizations, and 100 800 (95% UI, 64 000-140 400) deaths. In 2023-2024, people 65 years and older comprised 17.7% of the total US population but accounted for 47.9% (95% UI, 27.1-66.9) of COVID-19-associated illnesses, 64.3% (95% UI, 53.1-73.4) of outpatient visits, 67.6% (95% UI, 65.9-69.2) of hospitalizations, and 81.2% (95% UI, 70.2-90.6) of deaths. Conclusions and Relevance:In this cross-sectional study, despite declining from the first to the second surveillance period, the COVID-19 burden continued to have a large impact in the US, particularly among adults 65 years and older, underscoring the ongoing importance of prevention measures.

In the United States, annual influenza vaccination has been recommended for all persons aged ≥6 months, including during the 2025-26 season. Interim influenza vaccine effectiveness (VE) estimates were calculated for patients with acute respiratory illness-associated outpatient visits and hospitalizations from three U.S. respiratory virus VE networks during the 2025-26 influenza season, using a test-negative case-control design. Among children and adolescents aged <18 years, VE was 38%-41% against influenza outpatient visits and 41% against influenza-associated hospitalization. Among adults aged ≥18 years, VE was 22%-34% against influenza outpatient visits and 30% against influenza-associated hospitalization. Among children and adolescents, VE against influenza A ranged from 37% (against outpatient visits) to 42% (against hospitalization) across settings; among adults, VE against influenza A ranged from 30% (against hospitalization) to 34% (against outpatient visits) across settings. Among children and adolescents, VE against influenza A(H3N2)-associated outpatient visits was 35% and against influenza A(H3N2)-associated hospitalization was 38%. VE against influenza B outpatient visits ranged from 45%-71% among children and adolescents and was 63% among adults. Other estimates of VE were not statistically significant or were not reportable. Although interim influenza VE is lower during the 2025-26 influenza season than it was during recent influenza seasons, these findings demonstrate that influenza vaccination still provides protection against influenza. CDC recommends influenza vaccination; U.S. influenza vaccines remain available for persons aged ≥6 months.

Background:Patients hospitalised with influenza have heterogeneous clinical presentations and disease severity, which may complicate epidemiologic study design or interpretation. We applied latent class analysis to identify clinically distinct subgroups of adults hospitalised with influenza. Methods:We analysed cross-sectional study data on adults (≥18 years) hospitalised with laboratory-confirmed influenza from the population-based U.S. Influenza Hospitalization Surveillance Network (FluSurv-NET) including 13 states during 2017-2018 and 2018-2019 influenza seasons (October 1 through April 30). Adults were included if they were residents of the FluSurv-NET catchment area, hospitalised with laboratory-confirmed influenza during these two seasons, and had both the main case report form and the supplemental disease severity case report form completed. We constructed a latent class model to identify subgroups from multiple observed variables including baseline characteristics (age and comorbidities) and clinical course (symptoms at admission, respiratory support requirement, and development of new complications and exacerbations of underlying conditions). Findings:Among the 43,811 influenza-associated hospitalizations reported during the 2017-2018 and 2018-2019 influenza seasons, 15,873 (36.2%) were included in our analytic population: among them, 7069 (44.5%) were male and 8804 (55.5%) were female. We identified five subgroups. Subgroup A included persons of all ages with few comorbidities and 87.9% (255/290) of pregnant women. Subgroup B included older adults with comorbidities (cardiovascular disease (79.7% [3650/4581]) and diabetes (50.6% [2320/4581])). Almost all patients in subgroups C and D had asthma or chronic lung disease and high proportions with exacerbations of underlying conditions (59.7% [889/1489] and 65.1% [2274/3496], respectively). Subgroup E had the highest proportion with new complications (90.3% [1383/1531]). Subgroups D and E had the highest proportions with severe disease indicators: 21.0% (733/3496) and 50.4% (771/1531) required ICU admission, 7.2% (253/3496) and 28.0% (428/1531) required invasive mechanical ventilation, and 3.3% (116/3496) and 11.4% (174/1531) died in-hospital, respectively. Interpretation:The five identified subgroups of adults hospitalised with influenza had varying distributions of age, comorbid conditions, and clinical courses characterized by new complications versus exacerbations of existing conditions. Stratifying by these subgroups may strengthen analyses that assess the impact of influenza vaccination and antiviral treatment on risk of severe disease. Limitations included that results were based on a convenience sample within FluSurv-NET sites and were likely not representative of all adults hospitalised with influenza in the United States. Influenza testing was also clinician-driven, likely leading to under-ascertainment. Funding:Centers for Disease Control and Prevention.

Pregnant women and infants <6 months are at increased risk of severe influenza but can receive protection through influenza vaccination administered during pregnancy. Since influenza vaccination and virus transmission are seasonal in the United States, the calendar timing of pregnancy could impact the opportunity for influenza vaccination and risk of influenza for pregnant women and their infants. Using data on laboratory-confirmed influenza-associated hospitalizations from 2005/06 to 2022/23 (excluding the 2009/10 and 2020/21 seasons), we assessed the risk of hospitalization by influenza season timing and by pregnancy start and infant birth months. We then used 2022/23 influenza vaccination coverage data, and the weekly number of influenza positive specimens identified from 2005/06 to 2022/23 (excluding 2009/10 and 2020/21), to quantify how the opportunity for seasonal influenza vaccination and risk of influenza exposure varied with pregnancy and birth timing. We found that pregnancy start and infant birth months with the greatest hospitalization risk varied between seasons. In seasons peaking before the second week in January, the greatest percentage of hospitalizations occurred among pregnancies beginning March-June with births in October-December. In seasons peaking later, the greatest percentage occurred among pregnancies beginning May-August with births in November-January. Opportunities for protection through maternal vaccination also varied between pregnant women and infants who were most at risk for influenza. Most pregnant women at risk of influenza had an opportunity for current season vaccination during or before pregnancy (93-98 % depending on season timing). However, only 17-54 % of infants at risk had an opportunity for current season protection as many were born before most influenza vaccines were administered. Our results highlight heterogeneity in influenza vaccination opportunity and risk of influenza and severe disease among pregnant women and young infants and could inform strategies to increase vaccine-mediated protection in those at greatest risk.

Background Studies on SARS-CoV-2 household transmission often assume random mixing, overlooking detailed contact patterns and the timing of physical distancing. Methods To address this, we examined interactions within 280 households, including 280 index cases and 544 members, enrolled from April 2020 to April 2021 in Nashville, Tennessee, and central Wisconsin. Eligible households were enrolled within 7 days of index case symptom onset if at least one member was initially asymptomatic. Participants were monitored for 14 days, with symptoms and respiratory specimens collected daily, and contact data retrospectively assessed at three time points: the day before index case symptom onset, the day before enrollment, and 14 days post-enrollment. We fitted Exponential Random Graph Models to the contact pattern to identify drivers of household contact. We used the fitted household models to inform a two-level mixing model to account for community infection risk, and we calibrated it to the infection data. We then used the calibrated model to study different implementation of physical distancing. Results Contact patterns showed a significant reduction in physical interactions after infection awareness, particularly avoidance of index cases, with a 77% reduction in contact density (95% CI [65%-84%], p<0.001). Simulations from the two-level mixing model indicated that initiating contact reductions at symptom onset could lower secondary infections by over 25% in households of 4-5 members. Conclusions These results demonstrate how behavior changes following infection awareness reduce transmission. Implementing physical distancing earlier, at symptom onset, could further limit secondary infections and enhance household transmission control.

In late January 2025, CDC received anecdotal reports of children with influenza-associated acute necrotizing encephalopathy (ANE), a severe form of influenza-associated encephalopathy or encephalitis (IAE), including several fatal cases. In response, CDC examined trends in the proportions of cases with IAE among influenza-associated pediatric deaths reported during the 2010-11 through 2024-25 influenza seasons, including demographic and clinical characteristics of identified cases. CDC contacted state health departments to ascertain whether any pediatric influenza-associated deaths with IAE reported this season also had a diagnosis of ANE. Among 1,840 pediatric influenza-associated deaths during the 2010-11 through 2024-25 influenza seasons, 166 (9%) had IAE, ranging from 0% (2020-21 season) to 14% (2011-12 season); preliminary data for the 2024-25 season (through February 8, 2025) indicate that nine of 68 (13%) had IAE. Across seasons, the median age of patients with fatal IAE was 6 years; 54% had no underlying medical conditions, and only 20% had received influenza vaccination. Because no dedicated national surveillance for IAE or ANE exists, it is unknown if the numbers of cases this season vary from expected numbers. Health care providers should consider IAE in children with acute febrile illness and neurologic signs or symptoms lasting >24 hours. Evaluation should include testing for influenza and other viruses and neuroimaging; clinical management should include early antiviral treatment for suspected or confirmed influenza and supportive critical care management as needed. Influenza vaccination is recommended for all eligible persons aged ≥6 months as long as influenza viruses are circulating.

This report updates the 2024-25 recommendations of the Advisory Committee on Immunization Practices (ACIP) concerning the use of seasonal influenza vaccines in the United States. Routine annual influenza vaccination is recommended for all persons aged ≥6 months who do not have a contraindication to vaccination. Multiple formulations of the trivalent inactivated influenza vaccines (IIV3s), trivalent recombinant influenza vaccine (RIV3), and trivalent live attenuated influenza vaccine (LAIV3) are expected to be available for the 2025-26 influenza season. Updates for the 2025-26 season include 1) antigenic composition of 2025-26 U.S. seasonal influenza vaccines, 2) Food and Drug Administration (FDA) approval of FluMist (LAIV3) for self-administration or caregiver administration, 3) FDA approval of a change in age indication for Flublok (RIV3) from ≥18 years to ≥9 years, and 4) a new ACIP recommendation that children aged ≤18 years, pregnant women, and all adults receive seasonal influenza vaccines only in single-dose formulations that are free of thimerosal as a preservative. A comprehensive summary of recommendations, including those discussed in this report, as well as previous recommendations concerning topics not addressed in this report and that remain unchanged for the 2025-26 season, is available at Influenza | ACIP Recommendations for Vaccination. Additional background information also is available at Prevention and Control of Seasonal Influenza with Vaccines.

Understanding whether influenza vaccine promotion strategies produce community-wide indirect effects is important for establishing vaccine coverage targets and optimizing vaccine delivery. Empirical epidemiologic studies and mathematical models have been used to estimate indirect effects of vaccines but rarely for the same estimand in the same data set. Using these approaches together could be a powerful tool for triangulation in infectious disease epidemiology because each approach is subject to distinct sources of bias. We triangulated evidence about indirect effects from a school-located influenza vaccination program using 2 approaches: a difference-in-difference (DID) analysis and an age-structured, deterministic, compartmental model. The estimated indirect effect was substantially lower in the mathematical model than in the DID analysis (2.1% [95% Bayesian credible intervals, 0.4%-4.4%] vs 22.3% [7.6%-37.1%]). To explore reasons for differing estimates, we used sensitivity analyses and probabilistic bias analyses. When we constrained model parameters such that projections matched the DID analysis, results only aligned with the DID analysis with substantially lower preexisting immunity among school-age children and older adults. Conversely, DID estimates corrected for potential bias only aligned with mathematical model estimates under differential outcome misclassification. We discuss how triangulation using empirical and mathematical modeling approaches could strengthen future studies.

BACKGROUND:Coronavirus disease 2019 (COVID-19) burden is difficult to quantify with cases missed by surveillance systems. During COVID-19 Delta and Omicron BA.1-5 periods, we assessed the COVID-19 burden in New South Wales (NSW), Australia, from May 2021-July 2022 using a participatory surveillance system of self-reported respiratory disease and a database of people seeking healthcare. METHODS:To estimate community illness burden, we adjusted the NSW age-stratified non-case population by reported severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) percent positive and acute respiratory illness (ARI) rates. Hospitalization and death burden were estimated by adjusting reported rates to the NSW population and by the proportion of COVID-19 admissions attributable to COVID-19 illness. Burden estimates were compared to reported case counts. RESULTS:From May 2021-July 2022, an estimated 3,450,516 (95%CI: 2,847,355-4,119,472) symptomatic community ARI illnesses, 24,684 (95%CI: 20,714-29,144) hospitalizations, and 4,638 (95% CI: 3,263-6,049) deaths were attributable to COVID-19 in NSW. Reported cases (3,039,239) were 14% lower than the estimated symptomatic community illness burden but within the estimate's 95% confidence interval. Overall, 0.7% of symptomatic community illnesses resulted in hospitalization and 0.1% resulted in death. CONCLUSIONS:Estimated symptomatic case hospitalization and fatality risk could be used for COVID-19 modelling and forecasting.

Abstract Background To improve understanding of influenza and rurality, we investigated differences in influenza testing and anti-viral treatment rates between micropolitan (muSAs) and metropolitan statistical areas (MSAs) using national medical claims data over multiple influenza seasons. Methods Using billing data from the Centers for Medicare and Medicaid Services for those aged 65 years and older, we estimated weekly rates of ordered rapid influenza diagnostic tests (RIDT) and antivirals (AV) among Medicare enrollees by core-based statistical areas (CBSAs) during 2010–2016. We used Negative Binomial generalized mixed models to estimate adjusted rate ratios (aRR) between MSAs and muSAs, adjusting for clustering by CBSA plus explanatory variables. We ran models for all weeks and only high influenza activity weeks. Results For all weeks, the unadjusted rate of RIDTs was 1.97 per 10,000 people in MSAs compared with 2.69 in muSAs (Rate ratio (RR) = 0.73, 95% Confidence Interval (CI): 0.73–0.74) and of AVs was 1.85 in MSAs compared with 1.40 in muSAs (RR = 1.32, CI: 1.31–1.32). From the multivariate model, aRR for RIDTs was 0.82 (0.73–0.94) and for AVs was 1.12 (1.04–1.22) in MSAs versus muSAs. For high influenza activity weeks, aRR for RIDTs was 0.82 (0.73–0.92) and for AVs was 1.15 (1.06–1.24). All models found influenza testing rates higher in muSAs and treatment rates higher in MSAs. Conclusions Our study found lower testing and higher treatment in U.S. metropolitan versus micropolitan areas from 2010 to 2016 for those aged 65 years and older in our population. Identifying differences in influenza rates by rurality may improve public health response. Further research into the relationship of rurality and health disparities is needed.

Annual influenza vaccination is recommended for all persons aged ≥6 months in the United States. Interim influenza vaccine effectiveness (VE) was calculated among patients with acute respiratory illness-associated outpatient visits and hospitalizations from four VE networks during the 2024-25 influenza season (October 2024-February 2025). Among children and adolescents aged <18 years, VE against any influenza was 32%, 59%, and 60% in the outpatient setting in three networks, and against influenza-associated hospitalization was 63% and 78% in two networks. Among adults aged ≥18 years, VE in the outpatient setting was 36% and 54% in two networks and was 41% and 55% against hospitalization in two networks. Preliminary estimates indicate that receipt of the 2024-2025 influenza vaccine reduced the likelihood of medically attended influenza and influenza-associated hospitalization. CDC recommends annual receipt of an age-appropriate influenza vaccine by all eligible persons aged ≥6 months as long as influenza viruses continue to circulate locally.