Predicting Seasonal Influenza Hospitalizations Using an Ensemble Super Learner: A Simulation Study.

Accurate forecasts can inform response to outbreaks. Most efforts in influenza forecasting have focused on predicting influenza-like activity, with fewer on influenza-related hospitalizations. We conducted a simulation study to evaluate a super learner's predictions of 3 seasonal measures of influenza hospitalizations in the United States: peak hospitalization rate, peak hospitalization week, and cumulative hospitalization rate. We trained an ensemble machine learning algorithm on 15,000 simulated hospitalization curves and generated weekly predictions. We compared the performance of the ensemble (weighted combination of predictions from multiple prediction algorithms), the best-performing individual prediction algorithm, and a naive prediction (median of a simulated outcome distribution). Ensemble predictions performed similarly to the naive predictions early in the season but consistently improved as the season progressed for all prediction targets. The best-performing prediction algorithm in each week typically had similar predictive accuracy compared with the ensemble, but the specific prediction algorithm selected varied by week. An ensemble super learner improved predictions of influenza-related hospitalizations, relative to a naive prediction. Future work should examine the super learner's performance using additional empirical data on influenza-related predictors (e.g., influenza-like illness). The algorithm should also be tailored to produce prospective probabilistic forecasts of selected prediction targets.

Medically Attended Illness due to Respiratory Syncytial Virus Infection Among Infants Born in the United States Between 2016 and 2020.

BACKGROUND: Respiratory syncytial virus (RSV) is a leading cause of infant hospitalization in the United States. Preterm infants and those with select comorbidities are at highest risk of RSV-related complications. However, morbidity due to RSV infection is not confined to high-risk infants. We estimated the burden of medically attended (MA) RSV-associated lower respiratory tract infection (LRTI) among infants in the United States. METHODS: We analyzed commercial (MarketScan Commercial [MSC], Optum Clinformatics [OC]), and Medicaid (MarketScan Medicaid [MSM]) insurance claims data for infants born between April 2016 and February 2020. Using both specific and sensitive definitions of MA RSV LRTI, we estimated the burden of MA RSV LRTI during infants' first RSV season, stratified by gestational age, comorbidity status, and highest level of medical care associated with the MA RSV LRTI diagnosis. RESULTS: According to the specific definition 75.0% (MSC), 78.6% (MSM), and 79.6% (OC) of MA RSV LRTI events during infants' first RSV season occurred among term infants without known comorbidities. CONCLUSIONS: Term infants without known comorbidities account for up to 80% of the MA RSV LRTI burden in the United States during infants' first RSV season. Future prevention efforts should consider all infants.

Correlation of long-term care facility vaccination practices between seasons and resident types.

BACKGROUND: Influenza vaccination varies widely across long-term care facilities (LTCFs) due to staff behaviors, LTCF practices, and patient factors. It is unclear how seasonal LTCF vaccination varies between cohabitating but distinct short-stay and long-stay residents. Thus, we assessed the correlation of LTCF vaccination between these populations and across seasons. METHODS: The study design is a national retrospective cohort using Medicare and Minimum Data Set (MDS) data. Participants include U.S. LTCFs. Short-stay and long-stay Medicare-enrolled residents age ≥ 65 in U.S. LTCFs from a source population of residents during October 1st-March 31st in 2013-2014 (3,042,881 residents; 15,683 LTCFs) and 2014-2015 (3,143,174, residents; 15,667 LTCFs). MDS-assessed influenza vaccination was the outcome. Pearson correlation coefficients were estimated to assess seasonal correlations between short-stay and long-stay resident vaccination within LTCFs. RESULTS: The median proportion of short-stay residents vaccinated across LTCFs was 70.4% (IQR, 50.0-82.7%) in 2013-2014 and 69.6% (IQR, 50.0-81.6%) in 2014-2015. The median proportion of long-stay residents vaccinated across LTCFs was 85.5% (IQR, 78.0-90.9%) in 2013-2014 and 84.6% (IQR, 76.6-90.3%) in 2014-2015. Within LTCFs, there was a moderate correlation between short-stay and long-stay vaccination in 2013-2014 (r = 0.50, 95%CI: 0.49-0.51) and 2014-2015 (r = 0.53, 95%CI: 0.51-0.54). Across seasons, there was a moderate correlation for LTCFs with short-stay residents (r = 0.54, 95%CI: 0.53-0.55) and a strong correlation for those with long-stay residents (r = 0.68, 95%CI: 0.67-0.69). CONCLUSIONS: In LTCFs with inconsistent influenza vaccination across seasons or between populations, targeted vaccination protocols for all residents, regardless of stay type, may improve successful vaccination in this vulnerable patient population.

Persistence of Racial Inequities in Receipt of Influenza Vaccination Among Nursing Home Residents in the United States.

BACKGROUND: We sought to determine if racial differences in influenza vaccination among nursing home (NH) residents during the 2008-2009 influenza season persisted in 2018-2019. METHODS: We conducted a cross-sectional study of NHs certified by the Centers for Medicare & Medicaid Services during the 2018-2019 influenza season in US states with ≥1% Black NH residents and a White-Black gap in influenza vaccination of NH residents (N = 2 233 392) of at least 1 percentage point (N = 40 states). NH residents during 1 October 2018 through 31 March 2019 aged ≥18 years and self-identified as being of Black or White race were included. Residents' influenza vaccination status (vaccinated, refused, and not offered) was assessed. Multilevel modeling was used to estimate facility-level vaccination status and inequities by state. RESULTS: The White-Black gap in influenza vaccination was 9.9 percentage points. In adjusted analyses, racial inequities in vaccination were more prominent at the facility level than at the state level. Black residents disproportionately lived in NHs that had a majority of Blacks residents, which generally had the lowest vaccination. Inequities were most concentrated in the Midwestern region, also the most segregated. Not being offered the vaccine was negligible in absolute percentage points between White residents (2.6%) and Black residents (4.8%), whereas refusals were higher among Black (28.7%) than White residents (21.0%). CONCLUSIONS: The increase in the White-Black vaccination gap among NH residents is occurring at the facility level in more states, especially those with the most segregation.

On the Causal Interpretation of Rate-Change Methods: The Prior Event Rate Ratio and Rate Difference.

A growing number of studies use data before and after treatment initiation in groups exposed to different treatment strategies to estimate "causal effects" using a ratio measure called the prior event rate ratio (PERR). Here, we offer a causal interpretation for PERR and its additive scale analog, the prior event rate difference (PERD). We show that causal interpretation of these measures requires untestable rate-change assumptions about the relationship between 1) the change of the counterfactual rate before and after treatment initiation in the treated group under hypothetical intervention to implement the control strategy; and 2) the change of the factual rate before and after treatment initiation in the control group. The rate-change assumption is on the multiplicative scale for PERR but on the additive scale for PERD; the 2 assumptions hold simultaneously under testable, but unlikely, conditions. Even if investigators can pick the most appropriate scale, the relevant rate-change assumption might not hold exactly, so we describe sensitivity analysis methods to examine how assumption violations of different magnitudes would affect study results. We illustrate the methods using data from a published study of proton pump inhibitors and pneumonia.

Geographic Variation in Pneumonia and Influenza in Long-Term Care Facilities: A National Study.

There is large county-level geographic variation in pneumonia and influenza hospitalizations among short-stay and long-stay long-term care facility residents in the United States. Long-term care facilities in counties in the Southern and Midwestern regions had the highest rates of pneumonia and influenza from 2013 to 2015. Future research should identify reasons for these geographic differences.

Assessing the prior event rate ratio method via probabilistic bias analysis on a Bayesian network.

BACKGROUND: Unmeasured confounders are commonplace in observational studies conducted using real-world data. Prior event rate ratio (PERR) adjustment is a technique shown to perform well in addressing such confounding. However, it has been demonstrated that, in some circumstances, the PERR method actually increases rather than decreases bias. In this work, we seek to better understand the robustness of PERR adjustment. METHODS: We begin with a Bayesian network representation of a generalized observational study, which is subject to unmeasured confounding. Previous work evaluating PERR performance used Monte Carlo simulation to calculate joint probabilities of interest within the study population. Here, we instead use a Bayesian networks framework. RESULTS: Using this streamlined analytic approach, we are able to conduct probabilistic bias analysis (PBA) using large numbers of combinations of parameters and thus obtain a comprehensive picture of PERR performance. We apply our methodology to a recent study that used the PERR in evaluating elderly-specific high-dose (HD) influenza vaccine in the US Veterans Affairs population. That study obtained an HD relative effectiveness of 25% (95% CI: 2%-43%) against influenza- and pneumonia-associated hospitalization, relative to standard-dose influenza vaccine. In this instance, we find that the PERR-adjusted result is more like to underestimate rather than to overestimate the relative effectiveness of the intervention. CONCLUSIONS: Although the PERR is a powerful tool for mitigating the effects of unmeasured confounders, it is not infallible. Here, we develop some general guidance for when a PERR approach is appropriate and when PBA is a safer option.

Risk factors for pneumonia and influenza hospitalizations in long-term care facility residents: a retrospective cohort study.

BACKGROUND: Older adults who reside in long-term care facilities (LTCFs) are at particularly high risk for infection, morbidity and mortality from pneumonia and influenza (P&I) compared to individuals of younger age and those living outside institutional settings. The risk factors for P&I hospitalizations that are specific to LTCFs remain poorly understood. Our objective was to evaluate the incidence of P&I hospitalization and associated person- and facility-level factors among post-acute (short-stay) and long-term (long-stay) care residents residing in LTCFs from 2013 to 2015. METHODS: In this retrospective cohort study, we used Medicare administrative claims linked to Minimum Data Set and LTCF-level data to identify short-stay (< 100 days, index = admission date) and long-stay (100+ days, index = day 100) residents who were followed from the index date until the first of hospitalization, LTCF discharge, Medicare disenrollment, or death. We measured incidence rates (IRs) for P&I hospitalization per 100,000 person-days, and estimated associations with baseline demographics, geriatric syndromes, clinical characteristics, and medication use using Cox regression models. RESULTS: We analyzed data from 1,118,054 short-stay and 593,443 long-stay residents. The crude 30-day IRs (95% CI) of hospitalizations with P&I in the principal position were 26.0 (25.4, 26.6) and 34.5 (33.6, 35.4) among short- and long-stay residents, respectively. The variables associated with P&I varied between short and long-stay residents, and common risk factors included: advanced age (85+ years), admission from an acute hospital, select cardiovascular and respiratory conditions, impaired functional status, and receipt of antibiotics or Beers criteria medications. Facility staffing and care quality measures were important risk factors among long-stay residents but not in short-stay residents. CONCLUSIONS: Short-stay residents had lower crude 30- and 90-day incidence rates of P&I hospitalizations than long-stay LTCF residents. Differences in risk factors for P&I between short- and long-stay populations suggest the importance of considering distinct profiles of post-acute and long-term care residents in infection prevention and control strategies in LTCFs. These findings can help clinicians target interventions to subgroups of LTCF residents at highest P&I risk.

High-dose influenza vaccination and mortality among predominantly male, white, senior veterans, United States, 2012/13 to 2014/15.

IntroductionIt is unclear whether high-dose influenza vaccine (HD) is more effective at reducing mortality among seniors.AimThis study aimed to evaluate the relative vaccine effectiveness (rVE) of HD. MethodsWe linked electronic medical record databases in the Veterans Health Administration (VHA) and Medicare administrative files to examine the rVE of HD vs standard-dose influenza vaccines (SD) in preventing influenza/pneumonia-associated and cardiorespiratory mortality among VHA-enrolled veterans 65 years or older during the 2012/13, 2013/14 and 2014/15 influenza seasons. A multivariable Cox proportional hazards model was performed on matched recipients of HD vs SD, based on vaccination time, location, age, sex, ethnicity and VHA priority level. ResultsAmong 569,552 person-seasons of observation, 207,574 (36%) were HD recipients and 361,978 (64%) were SD recipients, predominantly male (99%) and white (82%). Pooling findings from all three seasons, the adjusted rVE estimate of HD vs SD during the high influenza periods was 42% (95% confidence interval (CI): 24-59) against influenza/pneumonia-associated mortality and 27% (95% CI: 23-32) against cardiorespiratory mortality. Residual confounding was evident in both early and late influenza periods despite matching and multivariable adjustment. Excluding individuals with high 1-year predicted mortality at baseline reduced the residual confounding and yielded rVE of 36% (95% CI: 10-62) and 25% (95% CI: 12-38) against influenza/pneumonia-associated and cardiorespiratory mortality, respectively. These were confirmed by results from two-stage residual inclusion estimations.DiscussionThe HD was associated with a lower risk of influenza/pneumonia-associated and cardiorespiratory death in men during the high influenza period.

The burden of respiratory infections among older adults in long-term care: a systematic review.

BACKGROUND: Respiratory infections among older adults in long-term care facilities (LTCFs) are a major global concern, yet a rigorous systematic synthesis of the literature on the burden of respiratory infections in the LTCF setting is lacking. To address the critical need for evidence regarding the global burden of respiratory infections in LTCFs, we assessed the burden of respiratory infections in LTCFs through a systematic review of the published literature. METHODS: We identified articles published between April 1964 and March 2019 through searches of PubMed (MEDLINE), EMBASE, and the Cochrane Library. Experimental and observational studies published in English that included adults aged ≥60 residing in LTCFs who were unvaccinated (to identify the natural infection burden), and that reported measures of occurrence for influenza, respiratory syncytial virus (RSV), or pneumonia were included. Disagreements about article inclusion were discussed and articles were included based on consensus. Data on study design, population, and findings were extracted from each article. Findings were synthesized qualitatively. RESULTS: A total of 1451 articles were screened for eligibility, 345 were selected for full-text review, and 26 were included. Study population mean ages ranged from 70.8 to 90.1 years. Three (12%) studies reported influenza estimates, 7 (27%) RSV, and 16 (62%) pneumonia. Eighteen (69%) studies reported incidence estimates, 7 (27%) prevalence estimates, and 1 (4%) both. Seven (27%) studies reported outbreaks. Respiratory infection incidence estimates ranged from 1.1 to 85.2% and prevalence estimates ranging from 1.4 to 55.8%. Influenza incidences ranged from 5.9 to 85.2%. RSV incidence proportions ranged from 1.1 to 13.5%. Pneumonia prevalence proportions ranged from 1.4 to 55.8% while incidence proportions ranged from 4.8 to 41.2%. CONCLUSIONS: The reported incidence and prevalence estimates of respiratory infections among older LTCF residents varied widely between published studies. The wide range of estimates offers little useful guidance for decision-making to decrease respiratory infection burden. Large, well-designed epidemiologic studies are therefore still necessary to credibly quantify the burden of respiratory infections among older adults in LTCFs, which will ultimately help inform future surveillance and intervention efforts.

Relative Vaccine Effectiveness of High-Dose Versus Standard-Dose Influenza Vaccines Among Veterans Health Administration Patients.

Background: We examined whether a high-dose inactivated influenza vaccine was more efficacious in preventing hospitalizations than a standard-dose vaccine in the Veterans Health Administration (VHA) senior population. Methods: This study estimated the relative vaccine effectiveness (rVE) of high dose versus standard dose using a retrospective cohort of VHA patients 65 years of age or older in the 2015-2016 influenza season. To adjust for measured confounders, we matched each high-dose recipient with up to 4 standard-dose recipients vaccinated at the same location within a 2-week period and having 2 or more pre-existing medical comorbidities. We used the previous event rate ratio method (PERR), a type of difference-in-differences analysis, to adjust for unmeasured confounders. Results: We evaluated 104965 standard-dose and 125776 high-dose recipients; matching decreased the population to 49091 standard-dose and 24682 high-dose recipients. The matched, PERR-adjusted rVE was 25% (95% confidence interval [CI], 2%-43%) against influenza- or pneumonia-associated hospitalization, 7% (95% CI, -2% to 14%) against all-cause hospitalization, 14% (95% CI, -8% to 32%) against influenza- or pneumonia-associated outpatient visit, 5% (95% CI, 2%-8%) against all-cause outpatient visit, and 38% (95% CI, -5% to 65%) against laboratory-confirmed influenza. Conclusions: In protecting senior VHA patients against influenza- or pneumonia-associated hospitalization, a high-dose influenza vaccine is more effective than a standard-dose vaccine.

Using an Inpatient Quality Improvement Curriculum for Internal Medicine Residents to Improve Pneumococcal Conjugate Vaccine Administration Rates.

BACKGROUND: Pneumococcal infections are an important source of morbidity and mortality in older adults and persons with compromised immune systems. New recommendations from the Advisory Committee on Immunization Practices (ACIP) became available September 2014, which included recommendations for the use of the 13-valent pneumococcal conjugate vaccine (PCV13). A study was conducted to increase the PCV13 vaccination rates of hospitalized patients at the White River Junction Veterans Affairs Medical Center (White River Junction, Vermont) through the use of a resident-driven quality improvement (QI) project. METHODS: From December 2014 through April 2016, 16 internal medicine inpatient residents addressed inpatient PCV13 vaccination rates by participating in the facility's QI curriculum. Eight Plan-Do-Study-Act cycles were used, including discharge template editing, electronic reminders, and the discovery of a vaccination administration documentation error in the record through data validation. The measure was the monthly percentage of patients who received PCV13 vaccination (vaccination completion rate) of those discharged from the hospital medicine service who were due for PCV13 vaccination. RESULTS: The percentage of veterans discharged with an up-to-date PCV13 vaccination on discharge increased from approximately 30% to 87% and was sustained. CONCLUSION: Despite being driven by many different residents, this project demonstrates that continuous improvement can be achieved through a structured and iterative process while providing active learning of core QI concepts to residents. It also displays a method in which new guidelines can be incorporated into practice in an effective manner. Finally, this project is an example of how resident-driven data validation can lead to further improvement.

Impact of The Daily Plan on Length of Stay and Readmission.

The Veterans Health Administration implemented The Daily Plan (TDP) to improve patient safety. We compared length of stay and readmission between intervention and control units. Length of stay decreased for both groups. Readmission rates increased for controls (21.3%-25.0%, P = .02) and barely changed for TDP units (21.7%-22.5%, P = .37). Although there were no efficiency improvements, TDP's ultimate goal was safety. Not all patient safety actions improve efficiency; nonetheless, their value continues.

Coronary and Cerebrovascular Events and Exacerbation of Existing Conditions After Laboratory-Confirmed Influenza Infection Among US Veterans: A Self-Controlled Case Series Study.

BACKGROUND: Influenza may contribute to coronary/cerebrovascular events and exacerbate underlying conditions. METHODS: We used self-controlled case series (SCCS) design to analyze data from US Veterans ≥18 years with coronary/cerebrovascular or exacerbation event +/-1 year of lab-confirmed influenza (LCI) during 2010-2018. We estimated the incidence ratio (IR) (95% CI) of the event for risk interval (Days 1-7 post-LCI) versus control interval (all other times +/-1 year of LCI) with fixed-effects conditional Poisson regression. We included biomarker data for mediation analysis. RESULTS: We identified 3439 episodes with coronary/cerebrovascular-related hospitalizations. IRs (95% CI) for LCI risk versus control interval were STEMI 0.6 (0.1, 4.4), NSTEMI 7.3 (5.8, 9.2), ischemic stroke 4.0 (3.0, 5.4), hemorrhagic stroke 6.2 (3.4, 11.5), and coronary spasm 1.3 (0.5, 3.0). IR significantly increased for NSTEMI and ischemic stroke among those ≥ 65 years. IR for NSTEMI and ischemic stroke dropped 26% and 10%, respectively, when white blood cell (WBC) and platelet count were considered. LCI was significantly associated with exacerbation of preexisting asthma, chronic obstructive pulmonary disease, and congestive heart failure. CONCLUSIONS: We found significant association between LCI and hospitalization for NSTEMI, ischemic stroke, and hemorrhagic stroke, the latter possibly due to unaccounted time-varying confounding in SCCS design.

Risk Analysis of Respiratory Syncytial Virus Among Infants in the United States by Birth Month.

BACKGROUND: Respiratory syncytial virus (RSV) is a major cause of morbidity and mortality among US infants. A child's calendar birth month determines their age at first exposure(s) to RSV. We estimated birth month-specific risk of medically attended (MA) RSV lower respiratory tract infection (LRTI) among infants during their first RSV season and first year of life (FYOL). METHODS: We analyzed infants born in the USA between July 2016 and February 2020 using three insurance claims databases (two commercial, one Medicaid). We classified infants' first MA RSV LRTI episode by the highest level of care incurred (outpatient, emergency department, or inpatient), employing specific and sensitive diagnostic coding algorithms to define index RSV diagnoses. In our main analysis, we focused on infants' first RSV season. In our secondary analysis, we compared the risk of MA RSV LRTI during infants' first RSV season to that of their FYOL. RESULTS: Infants born from May through September generally had the highest risk of first-season MA RSV LRTI-approximately 6-10% under the specific RSV index diagnosis definition and 16-26% under the sensitive. Infants born between October and December had the highest risk of RSV-related hospitalization during their first season. The proportion of MA RSV LRTI events classified as inpatient ranged from 9% to 54% (specific) and 5% to 33% (sensitive) across birth month and comorbidity group. Through the FYOL, the overall risk of MA RSV LRTI is comparable across birth months within each claims database (6-11% under the specific definition, 17-30% under the sensitive), with additional cases progressing to care at outpatient or ED settings. CONCLUSIONS: Our data support recent national recommendations for the use of nirsevimab in the USA. For infants born at the tail end of an RSV season who do not receive nirsevimab, a dose administered prior to the onset of their second RSV season could reduce the incidence of outpatient- and ED-related events.

Geographic Variation in Racial Disparities in Receipt of High-Dose Influenza Vaccine Among US Older Adults.

BACKGROUND: Racial disparities in receipt of high-dose influenza vaccine (HDV) have been documented nationally, but whether small-area geographic variation in such disparities exists remains unknown. We assessed the distribution of disparities in HDV receipt between Black and White traditional Medicare beneficiaries vaccinated against influenza within states and hospital referral regions (HRRs). METHODS: We conducted a nationally representative retrospective cohort study of 11,768,724 community-dwelling traditional Medicare beneficiaries vaccinated against influenza during the 2015-2016 influenza season (94.3% White and 5.7% Black). Our comparison was marginalized versus privileged racial group measured as Black versus White race. Vaccination and type of vaccine were obtained from Medicare Carrier and Outpatient files. Differences in the proportions of individuals who received HDV between Black and White beneficiaries within states and HRRs were used to measure age- and sex-standardized disparities in HDV receipt. We restricted to states and HRRs with ≥ 100 beneficiaries per age-sex strata per racial group. RESULTS: We detected a national disparity in HDV receipt of 12.8 percentage points (pps). At the state level, the median standardized HDV receipt disparity was 10.7 pps (minimum, maximum: 2.9, 25.6; n = 30 states). The median standardized HDV receipt disparity among HRRs was 11.6 pps (minimum, maximum: 0.4, 24.7; n = 54 HRRs). CONCLUSION: Black beneficiaries were less likely to receive HDV compared to White beneficiaries in almost every state and HRR in our analysis. The magnitudes of disparities varied substantially across states and HRRs. Local interventions and policies are needed to target geographic areas with the largest disparities to address these inequities.

Geospatial Distribution of Racial Disparities in Influenza Vaccination in Nursing Homes.

OBJECTIVES: This study aimed to assess the distribution of racial disparities in influenza vaccination between White and Black short-stay and long-stay nursing home residents among states and hospital referral regions (HRRs). DESIGN: Retrospective cohort study. SETTING AND PARTICIPANTS: We included short-stay and long-stay older adults residing in US nursing homes during influenza seasons between 2011 and 2018. Included residents were aged ≥65 years and enrolled in Traditional Medicare. Analyses were conducted using resident-seasons, whereby residents could contribute to one or more influenza seasons if they resided in a nursing home across multiple seasons. METHODS: Our comparison of interest was marginalized vs privileged racial group membership measured as Black vs White race. We obtained influenza vaccination documentation from resident Minimum Data Set assessments from October 1 through June 30 of a particular influenza season. Nonparametric g-formula was used to estimate age- and sex-standardized disparities in vaccination, measured as the percentage point (pp) difference in the proportions of individuals vaccinated between Black and White nursing home residents within states and HRRs. RESULTS: The study included 7,807,187 short-stay resident-seasons (89.7% White and 10.3% Black) in 14,889 nursing homes and 7,308,111 long-stay resident-seasons (86.7% White and 13.3% Black) in 14,885 nursing homes. Among states, the median age- and sex-standardized disparity between Black and White residents was 10.1 percentage points (pps) among short-stay residents and 5.3 pps among long-stay residents across seasons. Among HRRs, the median disparity was 8.6 pps among short-stay residents and 5.0 pps among long-stay residents across seasons. CONCLUSIONS AND IMPLICATIONS: Our analysis revealed that the magnitudes of vaccination disparities varied substantially across states and HRRs, from no disparity in vaccination to disparities in excess of 25 pps. Local interventions and policies should be targeted to high-disparity geographic areas to increase vaccine uptake and promote health equity.

Methods to account for measured and unmeasured confounders in influenza relative vaccine effectiveness studies: A brief review of the literature.

Observational seasonal influenza relative vaccine effectiveness (rVE) studies employ a variety of statistical methods to account for confounding and biases. To better understand the range of methods employed and implications for policy, we conducted a brief literature review. Across 37 included rVE studies, 10 different types of statistical methods were identified, and only eight studies reported methods to detect residual confounding, highlighting the heterogeneous state of the literature. To improve the comparability and credibility of future rVE research, researchers should clearly explain methods and design choices and implement methods to detect and quantify residual confounding.

Reply to letter to editor by Hadigal et al. regarding the immunogenicity and safety trial of high-dose influenza vaccine in adults aged ≥60 years.

Hadigal et al. argued the recommendation of high-dose influenza vaccine over standard-dose formulation is not supported by comparisons of numbers-needed-to-vaccinate (NNV) nor aligned with the WHO mandate of improving vaccine coverage. However, the authors' NNV calculation was inaccurate. A preferential recommendation for vaccines preventing influenza/complications can increase coverage. Furthermore, the impact of vaccination is a function of efficacy/effectiveness and the vaccine-preventable fraction of disease burden; therefore Hadigal et al. should interpret the absolute risk reduction by vaccination within the context of overall disease burden. To address the threat of COVID-19 pandemic, authorities should implement concomitant influenza/COVID-19 vaccination to reduce the burden of cocirculation of influenza and SARS- CoV- 2 viruses and increase the coverage of proven influenza vaccines as per WHO mandate.

Variation in influenza vaccine assessment, receipt, and refusal by the concentration of Medicare Advantage enrollees in U.S. nursing homes.

BACKGROUND: More older adults enrolled in Medicare Advantage (MA) are entering nursing homes (NHs), and MA concentration could affect vaccination rates through shifts in resident characteristics and/or payer-related influences on preventive services use. We investigated whether rates of influenza vaccination and refusal differ across NHs with varying concentrations of MA-enrolled residents. METHODS: We analyzed 2014-2015 Medicare enrollment data and Minimum Data Set clinical assessments linked to NH-level characteristics, star ratings, and county-level MA penetration rates. The independent variable was the percentage of residents enrolled in MA at admission and categorized into three equally-sized groups. We examined three NH-level outcomes including the percentages of residents assessed and appropriately considered for influenza vaccination, received influenza vaccination, and refused influenza vaccination. RESULTS: There were 936,513 long-stay residents in 12,384 NHs. Categories for the prevalence of MA enrollment in NHs were low (0% to 3.3%; n = 4131 NHs), moderate (3.4% to 18.6%; n = 4127 NHs) and high (>18.6%; n = 4126 NHs). Overall, 81.3% of long-stay residents received influenza vaccination and 14.3% refused the vaccine when offered. Adjusting for covariates, influenza vaccination rates among long-stay residents were higher in NHs with moderate (1.70 percentage points [pp], 95% confidence limits [CL]: 1.15 pp, 2.24 pp), or high (3.05 pp, 95% CL: 2.45 pp, 3.66 pp) MA versus the lowest prevalence of MA. Influenza vaccine refusal was lower in NHs with moderate (-3.10 pp, 95% CL: -3.53 pp, -2.68 pp), or high (-4.63 pp, 95% CL: -5.11 pp, -4.15 pp) MA compared with NHs with the lowest prevalence of MA. CONCLUSION: A higher concentration of long-stay NH residents enrolled in MA was associated with greater influenza vaccine receipt and lower vaccine refusal. As MA becomes a larger share of the Medicare program, and more MA beneficiaries enter NHs, decisionmakers need to consider how managed care can be leveraged to improve the delivery of preventive services like influenza vaccinations in NH settings.