High-Dose Quadrivalent Influenza Vaccine for Prevention of Cardiovascular and Respiratory Hospitalizations in Older Adults

BACKGROUND

We assessed the relative vaccine effectiveness (rVE) of high-dose quadrivalent influenza vaccine (QIV-HD) versus standard-dose quadrivalent influenza vaccine (QIV-SD) in preventing respiratory or cardiovascular hospitalizations in older adults.

METHODS

FinFluHD was a phase 3b/4 modified double-blind, randomized pragmatic trial. Enrolment of 121,000 adults ≥65 years was planned over three influenza seasons (October to December 2019-2021). Participants received a single injection of QIV-HD or QIV-SD. The primary endpoint was first occurrence of an unscheduled acute respiratory or cardiovascular hospitalization (ICD-10 primary discharge J/I codes), from ≥14 days post-vaccination until May 31. The study was terminated after one season due to COVID-19; follow-up data for 2019-2020 are presented.

RESULTS

33,093 participants were vaccinated (QIV-HD, n = 16,549; QIV-SD, n = 16,544); 529 respiratory or cardiovascular hospitalizations (QIV-HD, n = 257; QIV-SD, n = 272) were recorded. The rVE of QIV-HD versus QIV-SD to prevent respiratory/cardiovascular hospitalizations was 5.5% (95% CI, -12.4 to 20.7). When prevention of respiratory and cardiovascular hospitalizations were considered separately, rVE estimates of QIV-HD versus QIV-SD were 5.4% (95% CI, -28.0 to 30.1) and 7.1% (95% CI, -15.0 to 25.0), respectively. Serious adverse reactions were <0.01% in both groups.

CONCLUSIONS

Despite insufficient statistical power due to the impact of COVID-19, rVE point estimates demonstrated a trend toward a benefit of QIV-HD over QIV-SD. QIV-HD was associated with lower respiratory or cardiovascular hospitalization rates than QIV-SD, with a comparable safety profile. Adequately powered studies conducted over multiple influenza seasons are needed to determine statistical significance of QIV-HD compared with QIV-SD against preventing respiratory and cardiovascular hospitalizations.

TRIAL REGISTRATION

ClinicalTrials.gov number: NCT04137887.

Electronically Delivered Nudges to Increase Influenza Vaccination Uptake in Older Adults With Diabetes: A Secondary Analysis of the NUDGE-FLU Trial

Importance

Influenza vaccination is associated with a reduced risk of mortality in patients with diabetes, but vaccination rates remain suboptimal.

Objective

To assess the effect of electronic nudges on influenza vaccination uptake according to diabetes status.

Design, Setting, and Participants

The NUDGE-FLU (Nationwide Utilization of Danish Government Electronic Letter System for Increasing Influenza Vaccine Uptake) trial was a nationwide clinical trial of Danish citizens 65 years or older that randomized participants at the household level to usual care or 9 different electronic nudge letters during the 2022 to 2023 influenza season. End of follow-up was January 1, 2023. This secondary analysis of the NUDGE-FLU trial was performed from May to July 2023.

Intervention

Nine different electronic nudge letters designed to boost influenza vaccination were sent in September to October 2022. Effect modification by diabetes status was assessed in a pooled analysis of all intervention arms vs usual care and for individual letters.

Main Outcomes and Measures

The primary end point was receipt of a seasonal influenza vaccine.

Results

The trial included 964 870 participants (51.5% female; mean [SD] age, 73.8 [6.3] years); 123 974 had diabetes. During follow-up, 83.5% with diabetes vs 80.2% without diabetes received a vaccine (P < .001). In the pooled analysis, nudges improved vaccination uptake in participants without diabetes (80.4% vs 80.0%; difference, 0.37 percentage points; 99.55% CI, 0.08 to 0.66), whereas there was no evidence of effect in those with diabetes (83.4% vs 83.6%; difference, -0.19 percentage points; 99.55% CI, -0.89 to 0.51) (P = .02 for interaction). In the main results of NUDGE-FLU, 2 of the 9 behaviorally designed letters (cardiovascular benefits letter and a repeated letter) significantly increased uptake of influenza vaccination vs usual care; these benefits similarly appeared attenuated in participants with diabetes (cardiovascular gain letter: 83.7% vs 83.6%; difference, 0.04 percentage points; 99.55% CI, -1.52 to 1.60; repeated letter: 83.5% vs 83.6%; difference, -0.15 percentage points; 99.55% CI, -1.71 to 1.41) vs those without diabetes (cardiovascular gain letter: 81.1% vs 80.0%; difference, 1.06 percentage points; 99.55% CI, 0.42 to 1.70; repeated letter: 80.9% vs 80.0%; difference, 0.87 percentage points; 99.55% CI, 0.22 to 1.52) (P = .07 for interaction).

Conclusions and Relevance

In this exploratory subgroup analysis, electronic nudges improved influenza vaccination uptake in persons without diabetes, whereas there was no evidence of an effect in persons with diabetes. Trials are needed to investigate the effect of digital nudges specifically tailored to individuals with diabetes.

Trial Registration

ClinicalTrials.gov Identifier: NCT05542004.

High-dose influenza vaccine in older adults by age and seasonal characteristics: Systematic review and meta-analysis update

This updated systematic review and meta-analysis of randomized and observational studies published up to April 2023 assessed the relative performance of high-dose inactivated influenza vaccine (HD-IIV) and standard-dose influenza vaccines (SD-IIV) against influenza-associated outcomes in older adults (≥65 years). The analysis included studies conducted over 12 influenza seasons (2009/2010 to 2019/2020, 2021/2022), including over 45 million individuals aged ≥ 65 years, and showed that HD-IIV provided significantly better protection than SD-IIV against influenza-like illness and influenza-related hospitalizations, as well as cardiovascular, cardiorespiratory, and all-cause hospitalizations. Subgroup analyses showed HD-IIV consistently provided better protection than SD-IIV against influenza outcomes across the age range (65+, 75+ 85+ years), and regardless of the predominantly circulating influenza strain and vaccine antigenic match/mismatch. Randomized studies continue to drive high-quality evidence on the effectiveness of high-dose inactivated influenza vaccine relative to SD-IIV against severe influenza outcomes in adults aged ≥ 65 years, supported by observational data.

Electronic nudges to increase influenza vaccination uptake in Denmark: a nationwide, pragmatic, registry-based, randomised implementation trial

BACKGROUND

Influenza vaccination rates remain suboptimal despite effectiveness in preventing influenza infection and related complications. We investigated whether behavioural nudges, delivered via a governmental electronic letter system, would increase influenza vaccination uptake among older adults in Denmark.

METHODS

We did a nationwide, pragmatic, registry-based, cluster-randomised implementation trial during the 2022-23 influenza season in Denmark. All Danish citizens aged 65 years or older or turning 65 years by Jan 15, 2023 were included. We excluded individuals living in nursing homes and individuals who had an exemption from the Danish mandatory governmental electronic letter system. Households were randomly assigned (9:1:1:1:1:1:1:1:1:1) to usual care or nine different electronic letters designed on the basis of different behavioural nudging concepts. Data were sourced from nationwide Danish administrative health registries. The primary endpoint was receipt of influenza vaccination on or before Jan 1, 2023. The primary analysis assessed an analytical set of one randomly selected individual per household, and a sensitivity analysis included all randomly assigned individuals and accounted for within-household correlation. The trial is registered with ClinicalTrials.gov, NCT05542004.

FINDINGS

We identified 1 232 938 individuals aged 65 years or older in Denmark and excluded 56 436 (4·6%) individuals living in nursing homes and 211 632 (17·2%) with an exemption from the electronic letter system. We randomly assigned 964 870 (78·3%) participants across 691 820 households. Compared with usual care, influenza vaccination rates were higher in the group receiving an electronic letter highlighting potential cardiovascular benefits of vaccination (81·00% vs 80·12%; difference 0·89 percentage points [99·55% CI 0·29-1·48]; p<0·0001) and the group receiving repeated letters at randomisation and at day 14 (80·85% vs 80·12%; difference 0·73 percentage points [0·13-1·34]; p=0·0006). These strategies improved vaccination rates across major subgroups including those with and without established cardiovascular disease. The cardiovascular gain-framed letter was particularly effective among participants who had not been vaccinated for influenza in the previous season (p_interaction=0·0002). A sensitivity analysis of all randomly assigned individuals accounting for within-household clustering yielded similar findings.

INTERPRETATION

Electronically delivered letters highlighting potential cardiovascular benefits of influenza vaccination or sent again as a reminder significantly increased vaccination uptake across Denmark. Although the magnitude of effectiveness was modest, the low-touch, inexpensive, and highly scalable nature of these electronic letters might be informative for future public health campaigns.

FUNDING

Sanofi.

The Effect of Electronic Nudges on Influenza Vaccination Rate in Older Adults With Cardiovascular Disease: a Prespecified Analysis of the NUDGE-FLU Trial

Background: Influenza vaccines have been demonstrated to effectively reduce the incidence of influenza infection and potentially associated risks of cardiovascular events in patients with cardiovascular disease (CVD). Despite strong guideline and public health endorsements, global influenza vaccination rates in patients with CVD are highly variable. This prespecified analysis of NUDGE-FLU (Nationwide Utilization of Danish Government Electronic Letter System for Increasing InFLUenza Vaccine Uptake) examined the effect of digital behavioral nudges on influenza vaccine uptake based on the presence of cardiovascular disease. Methods: NUDGE-FLU was a randomized, pragmatic, nationwide, register-based trial including Danish citizens aged 65 years or older during the 2022-2023 influenza season. Households were randomized in a 9:1:1:1:1:1:1:1:1:1 ratio to usual care or 9 electronic letters with designs based on behavioral concepts. Danish nationwide registers were used to collect baseline and outcome data. The primary endpoint was receipt of an influenza vaccine on or before January 1, 2023. The effects of the intervention letters were examined according to the presence of cardiovascular disease and across cardiovascular subgroups including heart failure, ischemic heart disease, and atrial fibrillation. Results: Of 964,870 NUDGE-FLU participants from 691,820 households, 264,392 (27.4%) had CVD. During follow-up, 83.1% of participants with CVD vs 79.2% of participants without CVD received influenza vaccination (p<0.001). Compared with usual care, a letter emphasizing the potential cardiovascular benefits of influenza vaccination increased vaccination rates; this effect was consistent in participants with CVD (absolute difference +0.60 percentage points, 99.55% CI -0.48 to 1.68) and without CVD (+0.98 percentage points, 99.55% CI 0.27 to 1.70; P for interaction=0.41). A repeated letter strategy with a reminder follow-up letter 14 days later was also effective in increasing influenza vaccination, irrespective of CVD (CVD: absolute difference +0.80 percentage points, 99.55% CI -0.27 to 1.86; no CVD: +0.67 percentage points, 99.55% CI -0.06 to 1.40; P for interaction=0.77). Effectiveness of both nudging strategies was consistent across all major CVD subgroups. None of the other seven nudging strategies were effective, regardless of CVD status. Conclusions: Electronic letter interventions emphasizing the potential cardiovascular benefits of influenza vaccination and using a reminder letter strategy were similarly beneficial in increasing influenza vaccination rates among older adults with and without CVD and across cardiovascular subgroups. Electronic nudges may improve influenza vaccine uptake in individuals with CVD.

102. Efficacy and Effectiveness of High-Dose Influenza Vaccine in Older Adults by Age and Seasonal Characteristics: An Updated Systematic Review and Meta-Analysis

Background

High-dose influenza vaccine (HD-IIV) has been used extensively in older adults since its approval in 2009. Studies comparing HD-IIV to standard-dose influenza vaccines (SD-IIV) have demonstrated protection beyond influenza, including reduction of outcomes like cardiorespiratory and all-cause hospitalizations. This study is an update of previously-conducted reviews of the relative vaccine efficacy/effectiveness (rVE) of HD-IIV vs. SD-IIV in adults ≥65 years against influenza-associated outcomes from 2009-2020, with sub-analyses by seasonal and recipient characteristics.

Methods

An updated systematic review and meta-analysis was conducted for studies assessing the rVE of HD-IIV against probable/laboratory-confirmed influenza-like illness (ILI), emergency department (ED) and/or hospital admissions in adults ≥65 years. Results from individual seasons – stratified by outcome, subject characteristics, and influenza season, were meta-analyzed to estimate pooled rVEs of HD-IIV.

Results

19 studies from 11 consecutive seasons with over 45 million HD-IIV or SD-IIV recipients were meta-analyzed. Overall, HD-IIV demonstrated improved protection vs. SD-IIV against ILI (rVE=14.3%, 95%CI:4.2-23.3%), HD-IIV was more effective at preventing hospital/ED visits due to influenza (rVE=10.4%, 95%CI:6.8-13.9%), and hospitalizations due to influenza (rVE=11.2%, 95%CI:7.4-14.8%), pneumonia (rVE=27.3%, 95%CI:15.3-37.6%); pneumonia and influenza (rVE=13.4%, 95%CI:7.3-19.2%); respiratory (rVE=14.3%, 95%CI:8.5-20.0%), cardiovascular (rVE=13.1%, 95%CI:10.5-15.7%), and cardiorespiratory events (rVE=17.9%, 95%CI:15.0-20.8%); and all-causes (rVE=8.4%, 95%CI:5.7-11.0%). Pooled rVEs were similar in sub-analyses by dominant strain, antigenic match, and study type/setting. While all adults 65+ benefited from the use of HD-IIV, age-stratified analyses of the rVE of HD-IIV suggested additional relative benefit with increasing age.

Conclusion

Evidence over 11 consecutive influenza seasons from both randomized and observational studies suggests HD-IIV was consistently more effective than SD-IIV at reducing influenza and associated serious outcomes irrespective of recipient age and characteristics of the influenza season.

Disclosures

Jason K. Lee, MS, MBiotech, Sanofi: Employee|Sanofi: Stocks/Bonds Gary K. Lam, PharmD, RPh, Sanofi: Employee Rolan Vaisman, PharmD, RPh, Sanofi: Employee Kevin J. Yin, MD, MPH, PhD, Sanofi: Employee|Sanofi: Stocks/Bonds Bruce T. Seet, PhD, MBA, Sanofi: Employee|Sanofi: Stocks/Bonds Matthew M. Loiacono, PhD, MSc, Sanofi: Employee|Sanofi: Stocks/Bonds Sandrine I. Samson, PhD, Sanofi: Employee|Sanofi: Stocks/Bonds.

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.

Immunological non-inferiority and safety of a quadrivalent inactivated influenza vaccine versus two trivalent inactivated influenza vaccines in China: Results from two studies

WHO UNIVERSAL TRIAL NUMBERS (UTNS)

U1111-1174-4615 and U1111-1174-4698.

CLINICALTRIALS.GOV

NCT04210349 and NCT03430089.

Immunogenicity and safety of high-dose quadrivalent influenza vaccine in older adults in Taiwan: A phase III, randomized, multi-center study

BACKGROUND

High-dose influenza vaccine offers better protection against influenza/associated complications compared with standard-dose formulation. We evaluated immunogenicity and safety of high-dose influenza vaccine (QIV-HD) and standard-dose (QIV-SD) in older adults (≥ 65 years) in Taiwan.

METHODS

This was a phase III, randomized, modified double-blind, active-controlled, multi-center, descriptive study in older adults. Participants (N = 165) were randomized 1:1 to receive QIV-HD or QIV-SD vaccine (clinicaltrials.gov#NCT04537234).

RESULTS

For all four influenza strains, geometric means titers (GMTs) of hemagglutination inhibition were higher for the QIV-HD than QIV-SD with adjusted GMT ratios (95 % CI) of 2.65 (1.87-3.75) for A/H1N1; 1.76 (1.31-2.38) for A/H3N2; 2.60 (1.90-3.56) for B/Victoria; and 2.01 (1.57-2.56) for B/Yamagata. The seroconversion was higher for QIV-HD than QIV-SD with similar safety profiles across both groups.

CONCLUSION

QIV-HD was highly immunogenic for four influenza strains and have acceptable safety profile in older adults aged ≥ 65 years in Taiwan.

Safety and immunogenicity of a high-dose quadrivalent influenza vaccine administered concomitantly with a third dose of the mRNA-1273 SARS-CoV-2 vaccine in adults aged ≥65 years: a phase 2, randomised, open-label study

Background

Concomitant seasonal influenza vaccination with a COVID-19 vaccine booster could help to minimise potential disruption to the seasonal influenza vaccination campaign and maximise protection against both diseases among individuals at risk of severe disease and hospitalisation. This study aimed to assess the safety and immunogenicity of concomitant administration of high-dose quadrivalent influenza vaccine (QIV-HD) and a mRNA-1273 vaccine booster dose in older adults.

Methods

This study is an ongoing, phase 2, multicentre, open-label, descriptive trial at six clinical research sites in the USA. We describe the interim results up to 21 days after vaccination (July–August, 2021). Community-dwelling adults aged 65 years and older, who were previously vaccinated with a two-dose primary schedule of the mRNA-1273 SARS-CoV-2 vaccine, were eligible for inclusion. The second dose of the primary mRNA-1273 vaccination series was required to have been received at least 5 months before enrolment in the study. Participants were randomly assigned (1:1:1) using a permuted block method stratified by site and by age group (<75 years vs ≥75 years), to receive concomitant administration of QIV-HD and mRNA-1273 vaccine, QIV-HD alone, or mRNA-1273 vaccine alone. Randomisation lists, generated by Sanofi Pasteur biostatistics platform, were provided to study investigators for study group allocation. Unsolicited adverse events occurring immediately, solicited local and systemic reactions up to day 8, and unsolicited adverse events, serious adverse events, adverse events of special interest, and medically attended adverse events up to day 22 were reported. Haemagglutination inhibition antibody responses to influenza A/H1N1, A/H3N2, B/Yamagata, and B/Victoria strains and SARS CoV-2 binding antibody responses (SARS-CoV-2 pre-spike IgG ELISA) were assessed at day 1 and day 22. All analyses were descriptive. The study is registered with ClinicalTrials.gov, NCT04969276.

Findings

Between July 16 and Aug 31, 2021, 306 participants were enrolled and randomly assigned, of whom 296 received at least one vaccine dose (100 in the coadministration group, 92 in the QIV-HD, and 104 in the mRNA-1273 group). Reactogenicity profiles were similar between the coadministration and mRNA-1273 groups, with lower reactogenicity rates in the QIV-HD group (frequency of solicited injection site reactions 86·0% [95% CI 77·6–92·1], 91·3% [84·2–96·0], and 61·8% [50·9–71·9]; frequency of solicited systemic reactions 80·0%, [70·8–87·3], 83·7% [75·1–90·2], and 49·4% [38·7–60·2], respectively). Up to day 22, unsolicited adverse events were reported for 17·0% (95% CI 10·2–25·8) of participants in the coadministration group and 14·4% (8·3–22·7) of participants in the mRNA-1273 group, and tended to be reported at a slightly lower rate (10·9% [5·3–19·1]) in participants in the QIV-HD group. Seven participants each reported one medically attended adverse event (three in the coadministration group, one in the QIV-HD group, and three in the mRNA-1273 group). There were no serious adverse events, adverse events of special interest, or deaths. Haemagglutination inhibition antibody geometric mean titres increased from day 1 to day 22 to similar levels in the coadministration and QIV-HD groups, for each influenza strain (A/H1N1: 363 [95% CI 276–476] vs 366 [272–491]; A/H3N2: 286 [233–352] vs 315 [257–386]; B/Yamagata: 429 [350–525] vs 471 [378–588]; B/Victoria: 377 [325–438] vs 390 [327–465] for the coadministration and QIV-HD groups, respectively). SARS-CoV-2 binding antibody geometric mean concentrations also increased to similar levels in the coadministration and mRNA-1273 groups at day 22 (7634 [95% CI 6445–9042] and 7904 [6883–9077], respectively).

Interpretation

No safety concerns or immune interference were observed for concomitant administration of QIV-HD with mRNA-1273 booster in adults aged 65 years and older, supporting co-administration recommendations.

Funding

Sanofi Pasteur.

Digital intervention increases influenza vaccination rates for people with diabetes in a decentralized randomized trial

People with diabetes (PWD) have an increased risk of developing influenza-related complications, including pneumonia, abnormal glycemic events, and hospitalization. Annual influenza vaccination is recommended for PWD, but vaccination rates are suboptimal. The study aimed to increase influenza vaccination rate in people with self-reported diabetes. This study was a prospective, 1:1 randomized controlled trial of a 6-month Digital Diabetes Intervention in U.S. adults with diabetes. The intervention group received monthly messages through an online health platform. The control group received no intervention. Difference in self-reported vaccination rates was tested using multivariable logistic regression controlling for demographics and comorbidities. The study was registered at clinicaltrials.gov: NCT03870997. A total of 10,429 participants reported influenza vaccination status (5158 intervention, mean age (±SD) = 46.8 (11.1), 78.5% female; 5271 control, Mean age (±SD) = 46.7 (11.2), 79.4% female). After a 6-month intervention, 64.2% of the intervention arm reported influenza vaccination, vers us 61.1% in the control arm (diff = 3.1, RR = 1.05, 95% CI [1.02, 1.08], p = 0.0013, number needed to treat = 33 to obtain 1 additional vaccination). Completion of one or more intervention messages was associated with up to an 8% increase in vaccination rate (OR 1.27, 95% CI [1.17, 1.38], p < 0.0001). The intervention improved influenza vaccination rates in PWD, suggesting that leveraging new technology to deliver knowledge and information can improve influenza vaccination rates in high-risk populations to reduce public health burden of influenza. Rapid cycle innovation could maximize the effects of these digital interventions in the future with other populations and vaccines.

Influenza vaccination in immunocompromised populations: Strategies to improve immunogenicity

Immunocompromised individuals are at high risk of severe illness and complications from influenza infection. For this reason, immunization using inactivated influenza vaccines is recommended for transplant patients, individuals receiving immunosuppressant treatments, and other persons with immunodeficiency. However, these immunocompromised populations are more likely to have lower and non-protective responses to annual vaccination with a standard influenza vaccine. Here, we review strategies aimed to improve the immunogenicity of influenza vaccines in immunocompromised populations. The different strategies employed have included adjuvanted vaccines, high-dose vaccines, booster doses, intradermal vaccination, and temporary discontinuation of immunosuppressant treatment regimens. High-dose trivalent, inactivated, split-virus influenza vaccine (IIV3-HD) is so far one of the leading strategies for improving vaccine responses in HIV patients, transplant patients, and persons receiving immunosuppressant therapies for inflammatory diseases. Several studies in these populations have shown stronger humoral responses with IIV3-HD than existing standard-dose trivalent vaccine, and comparable safety. Accordingly, some scientific societies have stated that high-dose influenza vaccine could be a preferred option for immunocompromised patients. However, larger randomized controlled studies are needed to validate relative immunogenicity and safety of IIV3-HD and other enhanced vaccines and vaccination strategies in immunocompromised individuals.

Efficacy and effectiveness of high-dose influenza vaccine in older adults by circulating strain and antigenic match: An updated systematic review and meta-analysis

BACKGROUND

Influenza vaccine efficacy/effectiveness can vary from season to season due in part to the dominant circulating strains and antigenic matching. This study reviews the relative vaccine efficacy/effectiveness (rVE) of high-dose inactivated trivalent influenza vaccine (HD-IIV3) compared to standard-dose influenza vaccines (SD-IIV) in adults aged ≥ 65 years against influenza-associated outcomes. Additional sub-analyses of HD-IIV3 rVE were performed by the predominantly circulating influenza strain and the antigenic match or mismatch of the vaccine against the predominant circulating strains.

METHODS

An updated systematic review and meta-analysis was conducted for studies assessing the rVE of HD-IIV3 against probable/laboratory-confirmed influenza-like illness (ILI), hospital admissions, and death in adults aged ≥ 65 years. Results from individual seasons were extracted from the studies, and viral surveillance data were used to determine the dominant circulating strains and antigenic match for each season. Results were then stratified based on clinical outcomes and seasonal characteristics and meta-analyzed to estimate pooled rVEs of HD-IIV3.

RESULTS

15 publications were meta-analyzed after screening 1,293 studies, providing data on 10 consecutive influenza seasons and over 22 million individuals receiving HD-IIV3 in randomized and observational settings. Across all influenza seasons, HD-IIV3 demonstrated improved protection against ILI compared to SD-IIV (rVE = 15.9%, 95% CI: 4.1-26.3%). HD-IIV3 was also more effective at preventing hospital admissions from all-causes (rVE = 8.4%, 95% CI: 5.7-11.0%), as well as influenza (rVE = 11.7%, 95% CI: 7.0-16.1%), pneumonia (rVE = 27.3%, 95% CI: 15.3-37.6%), combined pneumonia/influenza (rVE = 13.4%, 95% CI: 7.3-19.2%) and cardiorespiratory events (rVE = 17.9%, 95% CI: 15.0-20.8%). Reductions in mortality due to pneumonia/influenza (rVE = 39.9%, 95% CI: 18.6-55.6%) and cardiorespiratory causes (rVE = 27.7%, 95% CI: 13.2-32.0%) were also observed. Similar pooled rVEs were observed in both matched and mismatched seasons and in seasons where A/H3N2 or A/H1N1 strains were predominantly circulating.

CONCLUSIONS

Evidence over 10 consecutive influenza seasons and in more than 34 million individuals aged ≥ 65 years suggests that HD-IIV3 is consistently more effective than SD-IIV at reducing influenza cases as well as influenza-associated clinical complications irrespective of circulating strain and antigenic match. A video summary of the article can be accessed via the Supplementary data link at the end of this article.

Quantifying the Impact of Influenza Among Persons With Type 2 Diabetes Mellitus: A New Approach to Determine Medical and Physical Activity Impact

BACKGROUND

We describe the impact of influenza on medical outcomes and daily activities among people with and without type 2 diabetes mellitus (T2DM).

METHODS

Retrospective cohort analysis of a US health plan offering a digital wellness platform connecting wearable devices capable of tracking steps, sleep, and heart rate. For the 2016 to 2017 influenza season, we compared adults with T2DM to age and gender matched controls. Medical claims were used to define cohorts and identify influenza events and outcomes. Digital tracking data were aggregated at time slices of minute-, day-, week-, and year-level. A pre-post study design compared the peri-influenza period (two weeks before and four weeks after influenza diagnosis) to the six-week preceding period (baseline).

RESULTS

A total of 54 656 T2DM and 113 016 non-DM controls were used for the study. People with T2DM had more influenza claims, vaccinations, and influenza antivirals per 100 people (1.96% vs 1.37%, 34.3% vs 24.3%, and 27.1 vs 22 respectively, P < .001). A total of 1086 persons with T2DM and 1567 controls had an influenza claim (47.4% male, median age 54, 6.4% vs 7.8% trackers, respectively). Glycemic events, pneumonia, and ischemic heart disease increased over baseline during the peri-influenza period for T2DM (1.74-, 7.4-, and 1.6-fold increase respectively, P < .01). In a device wearing subcohort, we observed 10 000 fewer steps surrounding the influenza event, with the lowest (5500 steps) two days postinfluenza. Average heart rate increased significantly (+5.5 beats per minute) one day prior to influenza.

CONCLUSION

Influenza increases rates of pneumonia, heart disease, and abnormal glucose levels among people with T2DM, and negatively impacts daily activities compared to controls.

The disease burden of influenza beyond respiratory illness

Although influenza is primarily considered a respiratory infection and causes significant respiratory mortality, evidence suggests that influenza has an additional burden due to broader consequences of the illness. Some of these broader consequences include cardiovascular events, exacerbations of chronic underlying conditions, increased susceptibility to secondary bacterial infections, functional decline, and poor pregnancy outcomes, all of which may lead to an increased risk for hospitalization and death. Although it is methodologically difficult to measure these impacts, epidemiological and interventional study designs have evolved over recent decades to better take them into account. Recognizing these broader consequences of influenza virus infection is essential to determine the full burden of influenza among different subpopulations and the value of preventive approaches. In this review, we outline the main influenza complications and societal impacts beyond the classical respiratory symptoms of the disease.

Comparing the impact of high-dose versus standard dose influenza vaccines on hospitalization cost for cardiovascular and respiratory diseases: Economic assessment in the US Veteran population during 5 respiratory seasons using an instrumental variable method

OBJECTIVES

Cost savings associated with high-dose (HD) as compared to standard-dose (SD) influenza vaccination in the United States (US) Veteran's Health Administration (VHA) population have been attributed to better protection against hospitalization for cardiac and respiratory diseases. The relative contribution of each of these disease categories to the reported savings remains to be explored.

METHODS

During a recently completed study of HD versus SD vaccine effectiveness (conducted in the VHA over five respiratory seasons from 2010/11 through 2014/15), we collected cost data for all healthcare services provided at both VHA and Medicare-funded facilities. In that analysis, we compared the costs of vaccination and hospital care for patients admitted with either cardiovascular or respiratory disease. Treatment selection bias and other confounding factors were adjusted using an instrumental variable (IV) method. In this brief report we use the same study cohort and methods to stratify the results by patients admitted for cardiovascular disease (CVD) and those admitted for respiratory disease.

RESULTS

We analyzed 3.5 million SD and 0.16 million HD person-seasons. The IV-adjusted rVEs were 14% (7-20%) against hospitalizations for CVD and 15% (5-25%) against respiratory hospitalizations. Net cost savings per HD recipient were $138 ($66-$200) for CVD related hospitalizations and $62 ($10-$107) for respiratory disease related hospitalizations.

CONCLUSIONS

In the US VHA population, the reduction in hospitalizations for CVD over five respiratory seasons contributed twice the cost savings (per HD recipient) of the reduction in hospitalizations for respiratory disease.

2745. Efficacy and Effectiveness of High-Dose Influenza Vaccine for Older Adults by Circulating Strain and Antigenic Match: A Systematic Review and Meta-Analysis

Background

Influenza vaccine efficacy/effectiveness can vary from season to season due in part to the dominant circulating strains and antigenic matching. This study reviews the relative vaccine efficacy/effectiveness (rVE) of high-dose inactivated trivalent influenza vaccine (HD-IIV3) compared with standard-dose influenza vaccines (SD-IIV3) in adults ≥65 years against influenza-associated outcomes across all influenza seasons, during seasons where A/H3N2 or A/H1N1 strains predominantly circulated, and where there was an antigenic match or mismatch of the vaccine and circulating strains.

Methods

A systematic review was conducted for studies assessing the rVE of HD-IIV3 against probable/laboratory-confirmed influenza-like illness (ILI), hospital admissions, and death in adults ≥65 years. Results from individual seasons were extracted from the identified studies, and surveillance data from each season were used to determine the dominant circulating strains and antigenic match. Results were then stratified based on clinical outcomes and seasonal characteristics and meta-analyzed to estimate pooled rVEs of HD-IIV3.

Results

11 studies were meta-analyzed after screening 1,018 studies, providing data on 9 consecutive influenza seasons and over 12 million individuals receiving HD-IIV3. Across all influenza seasons, HD-IIV3 demonstrated improved protection against ILI compared with SD-IIV3 (rVE = 15.9%, 95% CI: 4.1–26.3%). HD-IIV3 was also more effective at preventing hospital admissions from all-causes (rVE = 8.4%, 95% CI: 5.7–11.0%), as well as influenza (rVE = 16.1%, 95% CI: 7.4–24.1%), pneumonia (rVE = 27.3%, 95% CI: 15.3–37.6%), pneumonia/influenza (rVE = 13.4%, 95% CI: 7.3–19.2%) and cardiorespiratory events (rVE = 17.9%, 95% CI: 15.0–20.8%). Some numerical differences were observed in the pooled rVE of outcomes in matched and mismatched seasons and in seasons where A/H3N2 or A/H1N1 strains were predominantly circulating (Table 1).

Conclusion

Evidence over 9 influenza seasons suggest that HD-IIV3 is consistently more effective than SD-IIV3 at reducing the clinical outcomes associated with influenza infection irrespective of circulating strain and antigenic match. This study was funded by sanofi pasteur.

Disclosures

All authors: No reported disclosures.

Epidemiology and burden of influenza in healthy children aged 6 to 35 months: analysis of data from the placebo arm of a phase III efficacy trial

Background

Despite World Health Organization recommendations, in many countries young children are not targeted for influenza vaccination. To help inform influenza vaccination policy, we examined the occurrence and burden of influenza in healthy children aged 6 to 35 months using data from a recent phase III placebo-controlled influenza vaccine trial conducted in countries in the Northern and Southern Hemispheres.

Methods

This was an analysis of data from participants included in the placebo arm of a phase III clinical trial in healthy children aged 6 to 35 months (EudraCT no. 2013–001231-51). Included children had never been vaccinated for influenza and were observed for one influenza season. Outcome measures included the occurrence of influenza-like illness (ILI), laboratory-confirmed influenza, virus types/subtypes, severe symptoms and complications of confirmed influenza, and healthcare use associated with confirmed influenza.

Results

Data from 2210 participants were analysed. ILI was reported for 811 participants (36.7%). Of these, 255 participants (31.4%) had 263 virologically confirmed episodes of influenza. The overall influenza attack rate was 11.5%. The most common influenza virus detected was A(H3N2) (40.7%), followed by B/Yamagata (23.6%), A(H1N1) (18.6%), and B/Victoria (8.0%). Grade 3 fever was reported in 24.3% of confirmed episodes, acute lower respiratory infection in 8.7%, acute otitis media in 6.1%, and pneumonia in 1.9%. In most influenza episodes (93.2%), antipyretics, analgesics, or non-steroidal anti-inflammatory drugs were taken. Antibiotics were prescribed for 41.4% of influenza episodes. More than half of the influenza episodes (57.0%) resulted in outpatient visits. Influenza resulted in overnight hospitalisation in 1.1% of episodes.

Conclusions

Influenza is associated with a significant burden of disease in healthy children. This analysis also revealed that antibiotics continue to be frequently used for young children with influenza.

Trial registration

EudraCT no. 2013–001231-51.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3920-8) contains supplementary material, which is available to authorized users.

Impact of a quadrivalent inactivated influenza vaccine on influenza-associated complications and health care use in children aged 6 to 35 months: Analysis of data from a phase III trial in the Northern and Southern Hemispheres

BACKGROUND

A multi-season phase III trial conducted in the Northern and Southern Hemispheres demonstrated the efficacy of a quadrivalent split-virion inactivated influenza vaccine (IIV4) in children 6-35 months of age.

METHODS

Data collected during the phase III trial were analysed to examine the vaccine efficacy (VE) of IIV4 in preventing laboratory-confirmed influenza in age subgroups and to determine the relative risk for IIV4 vs. placebo for severe outcomes, healthcare use, and parental absenteeism from work associated with laboratory-confirmed influenza.

RESULTS

VE (95% confidence interval [CI]) to prevent laboratory-confirmed influenza due to any A or B strain was 54.76% (40.24-66.03%) for participants aged 6-23 months and 46.91% (23.57-63.53%) for participants aged 24-35 months. VE (95% CI) to prevent laboratory-confirmed influenza due to vaccine-similar strains was 74.51% (53.55-86.91%) for participants aged 6-23 months and 59.78% (19.11-81.25%) for participants aged 24-35 months. Compared to placebo, IIV4 reduced the risk (95% CI) by 31.28% (8.96-89.34%) for acute otitis media, 21.76% (6.46-58.51%) for acute lower respiratory infection, 40.80% (29.62-55.59%) for healthcare medical visits, 29.71% (11.66-67.23%) for parent absenteeism from work, and 39.20% (26.89-56.24%) for antibiotic use.

CONCLUSION

In children aged 6-35 months, vaccination with IIV4 reduces severe outcomes of influenza as well as the associated burden for their parents and the healthcare system. In addition, vaccination with IIV4 is effective at preventing against influenza in children aged 6-23 and 24-35 months.

TRIAL REGISTRATION

EudraCT no. 2013-001231-51.

Immunogenicity of high-dose trivalent inactivated influenza vaccine: a systematic review and meta-analysis

INTRODUCTION

High-dose trivalent, inactivated, split-virus influenza vaccine (IIV3-HD) has been available in the US since 2009 for adults aged ≥ 65 years. To better understand how IIV3-HD provides improved protection against influenza, we systematically reviewed clinical studies comparing immune responses to IIV3-HD and standard-dose trivalent vaccine (IIV3-SD).

AREAS COVERED

The primary objective was to determine the relative hemagglutination inhibition (HAI) antibody response of IIV3-HD vs. IIV3-SD in adults aged ≥ 65 years. Based on seven randomized studies including more than 18,500 adults aged ≥ 65 years, combined HAI geometric mean titer (GMT) ratios (95% confidence interval) approximately 1 month post-vaccination were 1.74 (1.65-1.83) for influenza A/H1N1, 1.84 (1.73-1.95) for influenza A/H3N2, and 1.47 (1.36-1.58) for influenza B. HAI GMT ratios in these studies were similar irrespective of sex, older age (≥ 75 years), frailty, and underlying conditions. Trends were similar for A/H3N2 neutralization and anti-neuraminidase antibody titers. In immunocompromised individuals, HAI GMT ratios were mostly > 1.

EXPERT OPINION

In agreement with its improved efficacy and effectiveness, IIV3-HD is consistently more immunogenic than IIV3-SD in adults aged ≥ 65 years. IIV3-HD also appears more immunogenic in immunocompromised individuals.

Quadrivalent inactivated influenza vaccine (VaxigripTetra™)

INTRODUCTION

VaxigripTetra™ (IIV4; Sanofi Pasteur) is a quadrivalent split-virion influenza vaccine approved in Europe in 2016 for individuals ≥ 3 years of age. IIV4 builds on the well-established record of the trivalent split-virion influenza vaccine (Vaxigrip®). Areas covered: This literature review summarizes the rationale for developing quadrivalent influenza vaccines and discusses the phase III clinical trial results supporting the immunogenicity, safety, and tolerability of IIV4. Expert commentary: IIV4 is immunogenic and well tolerated. Adding a second B strain to the trivalent split-virion influenza vaccine provides a superior immune response for the additional strain but does not reduce the immune response for the three other strains or negatively affect the safety profile. By offering broader protection against co-circulating influenza B lineages, IIV4 has the potential to further reduce influenza-related morbidity and mortality beyond that achieved with trivalent vaccines.

A trivalent, inactivated influenza vaccine (Vaxigrip®): summary of almost 50 years of experience and more than 1.8 billion doses distributed in over 120 countries

INTRODUCTION

Vaxigrip, a trivalent split-virion, inactivated vaccine available since 1968 has been in use longer than any other influenza vaccine. It is the most widely-used influenza vaccine, with more than 1.8 billion doses distributed in more than 120 countries. Areas covered: The significant body of evidence that confirms the efficacy, effectiveness, immunogenicity, and safety of Vaxigrip in healthy individuals of all ages and at-risk populations is summarized. The results from at least 15 randomized efficacy trials and 15 other studies have demonstrated that vaccination with Vaxigrip is efficacious against various clinical endpoints. It was estimated that more than 37 million laboratory-confirmed influenza episodes, 476,000 influenza-related hospitalizations, and 67,000 influenza-related deaths have been avoided by the more than 1.8 billion doses of Vaxigrip that have been distributed, emphasizing its important public health impact. Expert commentary: This strong evidence base in favor of Vaxigrip provides a robust foundation to support the implementation of the quadrivalent formulation. This quadrivalent formulation of Vaxigrip contains two A and two B influenza strains (VaxigripTetra), and has a similar immunogenicity and safety profile to the trivalent formulation while offering broader protection due to the addition of the second influenza B strain.

Vaccination of adults with 23-valent pneumococcal polysaccharide vaccine induces robust antibody responses against pneumococcal serotypes associated with serious clinical outcomes

PNEUMOVAX™ 23, a 23-valent polysaccharide pneumococcal vaccine (PPV23), covers 65% to 91% of the isolates recovered from adult cases of invasive pneumococcal disease. Several studies have demonstrated that pneumococcal serotypes 31, 11A, 35F, 17F, 3, 16F, 19F, 15B, and 10A are associated with higher case-fatality or meningitis rates than other pneumococcal serotypes. This study (U05-PnPS-403; EudraCT: 2008-003648-12) evaluated the immune response followings administration of PPV23 for 4 of these serotypes (10A, 11A, 15B, and 17F), that are included in PPV23 but not in licensed pneumococcal conjugate vaccines. Serotype-specific IgG geometric mean concentrations (GMCs) and geometric mean fold-rises (GMFRs) for these 4 serotypes were measured by a validated enzyme-linked immunosorbent assay (ELISA) in 104 subjects >50 y of age who were enrolled in a study evaluating the safety and immunogenicity of a single-dose of PPV23. At 1 month post-vaccination, GMCs for serotypes10A, 11A, 15B and 17F were 6.5, 4.3, 14.7, and 5.1 µg/mL, respectively. GMFRs from baseline were 9.0, 4.5, 8.4, and 11.5, respectively. The percentages of subjects achieving >2-fold increases in IgG GMCs between pre-vaccination and 1 month post-vaccination were 90%, 85%, 88% and 89%, respectively. In conclusion, PPV23 induces a robust immune response in adults to pneumococcal serotypes 10A, 11A, 15B, and 17F, which have been associated with elevated case-fatality or meningitis rates.

Annual public health and economic benefits of seasonal influenza vaccination: a European estimate

BACKGROUND

Vaccination is currently the most effective means of preventing influenza infection. Yet evidence of vaccine performance, and the impact and value of seasonal influenza vaccination across risk groups and between seasons, continue to generate much discussion. Moreover, vaccination coverage is below recommended levels.

METHODS

A model was generated to assess the annual public health benefits and economic importance of influenza vaccination in 5 WHO recommended vaccination target groups (children 6 - 23 months of age; persons with underlying chronic health conditions; pregnant women; health care workers; and, the elderly, 65 years of age) in 27 countries of the European Union. Model estimations were based on standard calculation methods, conservative assumptions, age-based and country-specific data.

RESULTS

Out of approximately 180 million Europeans for whom influenza vaccination is recommended, only about 80 million persons are vaccinated. Seasonal influenza vaccination currently prevents an annual average of between 1.6 million and 2.1 million cases of influenza, 45,300 to 65,600 hospitalizations, and 25,200 to 37,200 deaths. To reach the 75% vaccination coverage target set by the EU Council Recommendation in 2009, an additional 57.4 million person would need to be vaccinated in the elderly and other risk groups. By achieving the 75% target rate set in EU-27 countries, average annual influenza- related events averted would increase from current levels to an additional +1.6 to +1.7 million cases, +23,800 to +31,400 hospitalization, +9,800 to +14,300 deaths, +678,500 to +767,800 physician visits, and +883,800 to +1,015,100 lost days of work yearly. Influenza-related costs averted because of vaccination would increase by an additional + €190 to + €226 million yearly, in vaccination target groups.

CONCLUSIONS

Full implementation of current influenza vaccination recommendations of 75% vaccination coverage rate (VCR) in Europe by the 2014-2015 influenza season could immediately reduce an important public health and economic burden.

Acceptability of Intanza® 15 μg intradermal influenza vaccine in Belgium during the 2010-2011 influenza season

INTRODUCTION

Intradermal (ID) influenza vaccination induces an enhanced immune response in the elderly when compared with intramuscular (IM) vaccination. In 2009, an ID seasonal influenza vaccine (Intanza(®) [Sanofi Pasteur MSD, Lyon, France] 15 μg) was approved for use in individuals aged ≥ 60 years in Europe. This survey conducted in Belgium was the first in Europe to assess the acceptability of this vaccine in routine clinical practice by vaccinees and their general practitioners (GPs).

METHODS

GPs willing to use both the ID and IM influenza vaccines were selected during the 2010-2011 influenza season. Each GP recruited ≤ 10 patients aged ≥ 60 years who received the ID vaccine. Vaccinees and GPs completed questionnaires about their opinions on influenza vaccination and the acceptability of the ID influenza vaccine.

RESULTS

In total, 105 GPs and 837 vaccinees completed questionnaires. A high proportion of vaccinees (40.3%) was aged ≥ 75 years, and 95.5% had been vaccinated the previous year. The majority of vaccinees was very satisfied (70.0%) or satisfied (27.9%) with the ID vaccine. The main reasons for the high satisfaction rate were that the injection was not very painful, administration was quick, and the vaccinee felt confident about the micro-needle injection system. Most vaccinees (91.1%) who had previously received IM influenza vaccination preferred the ID vaccine, and 98.5% of vaccinees reported they would consider receiving the ID vaccine the following year. The majority of GPs was very satisfied (78.6%) or satisfied (18.4%) with the ID vaccine, and most GPs (87.6%) expressed a preference for the ID vaccine over IM influenza vaccine.

CONCLUSION

The ID influenza vaccine was well accepted by vaccinees and their GPs, who expressed a preference for the ID vaccine over conventional IM influenza vaccine. The availability of the ID influenza vaccine may help to improve uptake of seasonal influenza vaccination in the elderly.

Pneumococcal polysaccharide vaccination for adults: new perspectives for Europe

Vaccination is the only public-health measure likely to reduce the burden of pneumococcal diseases. In 2010, a group of European experts reviewed evidence on the burden of pneumococcal disease and the immunogenicity, clinical effectiveness and cost-effectiveness of vaccination with 23-valent pneumococcal polysaccharide vaccine (PPV23). They also considered issues affecting the future use of PPV23 and pneumococcal conjugate vaccines in the elderly and adults at high risk of pneumococcal disease. PPV23 covers 80-90% of the serotypes responsible for invasive pneumococcal disease in Europe. Primary vaccination and revaccination with PPV23 are well tolerated, induce robust, long-lasting immune responses in elderly adults and are cost effective. Ensuring protection against pneumococcal disease requires monitoring of the changing epidemiology of pneumococcal serotypes causing invasive pneumococcal disease and improving vaccine coverage. In the future, it will be critically important for pneumococcal vaccination recommendations for elderly adults to be based on comparative evaluations of PPV23 and newer pneumococcal conjugate vaccines with regard to their long-term immunogenicity, clinical effectiveness and cost-effectiveness.

Overview of vaccination policies for the elderly in Western European countries

Age-related changes in the immune system are associated with increased susceptibility to infections, greater disease severity and poorer outcomes in the elderly compared with young adults. Both influenza and pneumonia are important causes of morbidity and mortality in the elderly, and herpes zoster also represents an important disease burden in this population. Vaccinations against influenza and Streptococcus pneumoniae (pneumococcus) have been shown to reduce the incidence of influenza and invasive pneumococcal disease, respectively, in the elderly. In addition, as is the case with diphtheria/tetanus and herpes zoster vaccines, they can help to reduce the associated burden of disease in vaccinated individuals. Despite the evidence of these benefits, there are considerable variations among the countries of Western Europe in their policies for vaccination in the elderly. Western European countries face the prospect of a population in which the proportion of elderly people is increasing, with a consequent increase in demand on the healthcare system. Acknowledgement of the benefits of vaccination in the elderly, together with comprehensive vaccination policies for this age group, could help to reduce some of these demands.

Roles for common cytokine receptor gamma-chain-dependent cytokines in the generation, differentiation, and maturation of NK cell precursors and peripheral NK cells in vivo

NK cells differentiate in adult mice from bone marrow hemopoietic progenitors. Cytokines, including those that signal via receptors using the common cytokine receptor gamma-chain (gamma(c)), have been implicated at various stages of NK cell development. We have previously described committed NK cell precursors (NKPs), which have the capacity to generate NK cells, but not B, T, erythroid, or myeloid cells, after in vitro culture or transfer to a fetal thymic microenvironment. NKPs express the CD122 Ag (beta chain of the receptors for IL-2/IL-15), but lack other mature NK markers, including NK1.1, CD49b (DX5), or members of the Ly49 gene family. In this report, we have analyzed the roles for gamma(c)-dependent cytokines in the generation of bone marrow NKP and in their subsequent differentiation to mature NK cells in vivo. Normal numbers of NKPs are found in gamma(c)-deficient mice, suggesting that NK cell commitment is not dependent on IL-2, IL-4, IL-7, IL-9, IL-15, or IL-21. Although IL-2, IL-4, and IL-7 have been reported to influence NK cell differentiation, we find that mice deficient in any or all of these cytokines have normal NK cell numbers, phenotype, and effector functions. In contrast, IL-15 plays a dominant role in early NK cell differentiation by maintaining normal numbers of immature and mature NK cells in the bone marrow and spleen. Surprisingly, the few residual NK cells generated in absence of IL-15 appear relatively mature, expressing a variety of Ly49 receptors and demonstrating lytic and cytokine production capacity.

Combined deficiency in IkappaBalpha and IkappaBepsilon reveals a critical window of NF-kappaB activity in natural killer cell differentiation

Nuclear factor kappaB (NF-kappaB) transcription factors are key regulators of immune, inflammatory, and acute-phase responses and are also implicated in the control of cell proliferation and apoptosis. While perturbations in NF-kappaB activity impact strongly on B- and T-cell development, little is known about the role for NF-kappaB in natural killer (NK) cell differentiation. Inhibitors of NF-kappaB (IkappaBs) act to restrain NF-kappaB activation. We analyzed the cell-intrinsic effects of deficiencies in 2 IkappaB members (IkappaBalpha and IkappaBepsilon) on NK cell differentiation. Neither IkappaBalpha nor IkappaBepsilon deficiency had major effects on NK cell generation, while their combined absence led to NF-kappaB hyperactivation, resulting in reduced NK cell numbers, incomplete NK cell maturation, and defective interferon gamma (IFN-gamma) production. Complementary analysis of transgenic mice expressing an NF-kappaB-responsive reporter gene showed increased NF-kappaB activity at the stage of NK cell development corresponding to the partial block observed in IkappaBalpha x IkappaBepsilon-deficient mice. These results define a critical window in NK cell development in which NF-kappaB levels may be tightly controlled.

GATA-3 promotes maturation, IFN-gamma production, and liver-specific homing of NK cells

The GATA-3 transcription factor has a determinant role in T cell specification and is an essential mediator of T helper 2-type polarized immune responses. While both committed NK precursors and mature NK cells express GATA-3, a role of this transcription factor in murine NK cell differentiation is not known. We found that NK cells, in contrast to T cells, can be generated in the absence of GATA-3. However, while GATA-3 antagonizes IFN-gamma production in differentiating T cells, GATA-3-deficient NK cells paradoxically produced less IFN-gamma compared to control NK cells and failed to provide early protection in vivo against infection with Listeria monocytogenes. Surprisingly, GATA-3 was essential for NK cell homing to the liver. Our results suggest that GATA-3 promotes NK cell maturation and acts in this lineage to specify distinct effector phenotypes.

Functional dichotomy in natural killer cell signaling: Vav1-dependent and -independent mechanisms

The product of the protooncogene Vav1 participates in multiple signaling pathways and is a critical regulator of antigen-receptor signaling in B and T lymphocytes, but its role during in vivo natural killer (NK) cell differentiation is not known. Here we have studied NK cell development in Vav1-/- mice and found that, in contrast to T and NK-T cells, the absolute numbers of phenotypically mature NK cells were not reduced. Vav1-/- mice produced normal amounts of interferon (IFN)-gamma in response to Listeria monocytogenes and controlled early infection but showed reduced tumor clearance in vivo. In vitro stimulation of surface receptors in Vav1-/- NK cells resulted in normal IFN-gamma production but reduced tumor cell lysis. Vav1 was found to control activation of extracellular signal-regulated kinases and exocytosis of cytotoxic granules. In contrast, conjugate formation appeared to be only mildly affected, and calcium mobilization was normal in Vav1-/- NK cells. These results highlight fundamental differences between proximal signaling events in T and NK cells and suggest a functional dichotomy for Vav1 in NK cells: a role in cytotoxicity but not for IFN-gamma production.

Differential requirement for the transcription factor PU.1 in the generation of natural killer cells versus B and T cells

PU.1 is a member of the Ets family of transcription factors required for the development of various lymphoid and myeloid cell lineages, but its role in natural killer (NK) cell development is not known. The study shows that PU.1 is expressed in NK cells and that, on cell transfer into alymphoid Rag2/gammac(-/-) mice, hematopoietic progenitors of PU.1(-/-) fetal liver cells could generate functional NK cells but not B or T cells. Nevertheless, the numbers of bone marrow NK cell precursors and splenic mature NK cells were reduced compared to controls. Moreover, PU.1(-/-) NK cells displayed reduced expression of the receptors for stem cell factor and interleukin (IL)-7, suggesting a nonredundant role for PU.1 in regulating the expression of these cytokine receptor genes during NK cell development. PU.1(-/-) NK cells also showed defective expression of inhibitory and activating members of the Ly49 family and failed to proliferate in response to IL-2 and IL-12. Thus, despite the less stringent requirement for PU.1 in NK cell development compared to B and T cells, PU.1 regulates NK cell differentiation and homeostasis.