Review of Analyses Estimating Relative Vaccine Effectiveness of Cell-Based Quadrivalent Influenza Vaccine in Three Consecutive US Influenza Seasons

The economic rationale for cell-based influenza vaccines in children and adults: A review of cost-effectiveness analyses

Seasonal influenza significantly affects both health and economic costs in children and adults. This narrative review summarizes published cost-effectiveness analyses (CEAs) of cell-based influenza vaccines in children and adults <65 years of age, critically assesses the assumptions and approaches used in these analyses, and considers the role of cell-based influenza vaccines for children and adults. CEAs from multiple countries demonstrated the cost-effectiveness of cell-based quadrivalent influenza vaccines (QIVc) compared with egg-based trivalent/quadrivalent influenza vaccines (TIVe/QIVe). CEA findings were consistent across models relying on different relative vaccine effectiveness (rVE) estimate inputs, with the rVE of QIVc versus QIVe ranging from 8.1% to 36.2% in favor of QIVc. Across multiple scenarios and types of analyses, QIVc was consistently cost-effective compared with QIVe, including in children and adults across different regions of the world.

Comparative Effectiveness of the Bivalent (Original/Omicron BA.4/BA.5) mRNA COVID-19 Vaccines mRNA-1273.222 and BNT162b2 Bivalent in Adults with Underlying Medical Conditions in the United States

BACKGROUND/OBJECTIVES

This retrospective cohort study evaluated the relative vaccine effectiveness (rVE) of two bivalent (original/Omicron BA.4/BA.5) vaccines mRNA-1273.222 versus the BNT162b2 Bivalent in preventing COVID-19-related outcomes in adults with underlying medical conditions associated with increased risk for severe COVID-19.

METHODS

In a linked electronic health record/claims dataset, US adults (≥18 years) with ≥1 underlying medical condition of interest who received either the bivalent vaccine between 31 August 2022 and 28 February 2023 were identified. The inverse probability of treatment weighting was used to adjust for cohort differences. Cohorts were followed up for COVID-19-related hospitalizations and outpatient encounters until 31 May 2023. Hazard ratios and rVEs were estimated using Cox regression. Subgroup analyses were performed on individuals with pre-specified comorbid conditions.

RESULTS

757,572 mRNA-1273.222 and 1,204,975 BNT162b2 Bivalent recipients were identified. The adjusted rVE over a median follow-up of 198 days was 10.9% (6.2%-15.2%) against COVID-19-related hospitalization and 3.2% (1.7%-4.7%) against COVID-19-related outpatient encounters. rVE estimates for COVID-19 hospitalizations among subgroups with comorbid conditions were as follows: diabetes 15.1% (8.7%-21.0%), cerebro- and cardiovascular disease 14.7% (9.0%-20.1%), chronic lung disease 11.9% (5.1%-18.2%), immunocompromised 15.0% (7.2%-22.2%), chronic kidney disease 8.4% (0.5%-15.7%).

CONCLUSIONS

Overall, among adults with underlying medical conditions, mRNA-1273.222 was more effective than BNT162b2 Bivalent, especially in preventing COVID-19-related hospitalizations.

Differential Induction of Interferon-Stimulated Genes by Cell-Based Versus Egg-Based Quadrivalent Influenza Vaccines in Children During the 2018-2019 Season

BACKGROUND

Cell-based quadrivalent-inactivated influenza vaccine has been shown to have higher vaccine effectiveness than traditional egg-based quadrivalent-inactivated influenza vaccine. This is observed despite similar levels of serum hemagglutinin antibodies induced by each vaccine.

METHODS

In this study, we examine peripheral immune activation after egg-based or cell-based influenza vaccination in a clinical trial in children. Peripheral blood mononuclear cells were isolated, and ribonucleic acid was sequenced from 81 study participants (41 Fluzone, egg based and 40 Flucelvax, cell based) pre- and 7 days postvaccination. Seroconversion was assessed by hemagglutinin inhibition assay. Differential gene expression was determined and pathway analysis was conducted.

RESULTS

Cell-based influenza vaccine induced greater interferon-stimulated and innate immune gene activation compared with egg-based influenza vaccine. Participants who seroconverted had increased interferon-signaling activation versus those who did not seroconvert.

CONCLUSIONS

These data suggest that cell-based influenza vaccine stimulates immune activation differently from egg-based influenza vaccine, shedding light on reported differences in vaccine effectiveness.

Relative Vaccine Effectiveness of Cell- vs Egg-Based Quadrivalent Influenza Vaccine Against Test-Confirmed Influenza Over 3 Seasons Between 2017 and 2020 in the United States

Background

Influenza vaccine viruses grown in eggs may acquire egg-adaptive mutations that may reduce antigenic similarity between vaccine and circulating influenza viruses and decrease vaccine effectiveness. We compared cell- and egg-based quadrivalent influenza vaccines (QIVc and QIVe, respectively) for preventing test-confirmed influenza over 3 US influenza seasons (2017-2020).

Methods

Using a retrospective test-negative design, we estimated the relative vaccine effectiveness (rVE) of QIVc vs QIVe among individuals aged 4 to 64 years who had an acute respiratory or febrile illness and were tested for influenza in routine outpatient care. Exposure, outcome, and covariate data were obtained from electronic health records linked to pharmacy and medical claims. Season-specific rVE was estimated by comparing the odds of testing positive for influenza among QIVc vs QIVe recipients. Models were adjusted for age, sex, geographic region, influenza test date, and additional unbalanced covariates. A doubly robust approach was used combining inverse probability of treatment weights with multivariable regression.

Results

The study included 31 824, 33 388, and 34 398 patients in the 2017-2018, 2018-2019, and 2019-2020 seasons, respectively; ∼10% received QIVc and ∼90% received QIVe. QIVc demonstrated superior effectiveness vs QIVe in prevention of test-confirmed influenza: rVEs were 14.8% (95% CI, 7.0%-22.0%) in 2017-2018, 12.5% (95% CI, 4.7%-19.6%) in 2018-2019, and 10.0% (95% CI, 2.7%-16.7%) in 2019-2020.

Conclusions

This study demonstrated consistently superior effectiveness of QIVc vs QIVe in preventing test-confirmed influenza over 3 seasons characterized by different circulating viruses and degrees of egg adaptation.

Estimates of Seasonal Influenza Burden That Could Be Averted by Improved Influenza Vaccines in the Australian Population Aged Under 65 Years, 2015-2019

BACKGROUND

The interpretation of relative vaccine effectiveness (rVE) of improved influenza vaccines is complex. Estimation of burden averted is useful to contextualise their potential impact across different seasons. For the population aged under 65 years in Australia, this study estimated the additional morbidity and mortality that could be averted using improved influenza vaccines.

METHODS

We used observed, season-specific (2015-2019) influenza notification and influenza-coded hospitalisation frequencies and published modelled estimates of influenza-associated hospitalisations and deaths that occurred under the prevailing influenza vaccination coverage scenario. After back-calculating to the estimated burden in the population without vaccination, we applied published standard influenza vaccine effectiveness and coverage estimates to calculate the burden potentially averted by standard and improved influenza vaccines. A plausible range of rVE values were used, assuming 50% coverage.

RESULTS

The percentage point difference in absolute vaccine effectiveness (VE) of an improved vaccine compared to a standard vaccine is directly proportional to its rVE and inversely proportional to the effectiveness of the standard vaccine. The incremental burden averted by an improved vaccine is a function of both its difference in absolute VE and the severity of the influenza season. Assuming an rVE of 15% with 50% coverage, the improved vaccine was estimated to additionally avert 1517 to 12,641 influenza notifications, 287 to 1311 influenza-coded hospitalisations and 9 to 33 modelled all-cause influenza deaths per year compared to the standard vaccine.

CONCLUSIONS

Improved vaccines can have substantial clinical and population impact, particularly when the effectiveness of standard vaccines is low, and burden is high.

Cost-effectiveness analysis of cell-based versus egg-based quadrivalent influenza vaccines in the pediatric population in Taiwan

Cell-based influenza vaccines avoid egg-adaptive mutations, potentially improving vaccine effectiveness. We assessed the one-season cost-effectiveness of cell-based quadrivalent influenza vaccine (QIVc) against that of egg-derived quadrivalent influenza vaccines (QIVe) in children (6 months to 17 years of age) from payer and societal perspectives in Taiwan using an age-stratified static model. Base case and high egg adaptation scenarios were assessed. Deterministic and probabilistic sensitivity analyses were performed. The incremental cost-effectiveness ratio (ICER) threshold in Taiwan was assumed to be USD 99 177/quality-adjusted life year (QALY). Compared to QIVe, QIVc would prevent 15 665 influenza cases, 2244 complicated cases, and 259 hospitalizations per year. The base case ICER was USD 68 298/QALY and USD 40 085/QALY from the payer and societal perspective, respectively. In the high egg adaptation scenario, the ICER was USD 45 782/QALY from the payer's perspective and USD 17 489/QALY from the societal perspective. Deterministic sensitivity analyses indicated that infection incidence rate, vaccination coverage, and prevalence of the A/H3N2 strain were the main drivers of ICER. In conclusion, switching the immunization strategy from QIVe to QIVc is predicted to reduce the influenza-associated disease burden and be cost-effective for the pediatric population in Taiwan. The potential benefits of QIVc would be even higher during influenza seasons with high levels of egg adaptation.

Modelling the population-level benefits and cost-effectiveness of cell-based quadrivalent influenza vaccine for children and adolescents aged 6 months to 17 years in the US

BACKGROUND

Cell-based quadrivalent influenza vaccines (QIVc) can increase effectiveness against seasonal influenza by avoiding mismatch from egg adaption of vaccine viruses. This study evaluates the population-level cost-effectiveness and impacts on health outcomes of QIVc versus an egg-based vaccine (QIVe) in children aged 6 months to 17 years in the US.

RESEARCH DESIGN AND METHODS

A dynamic age-structured susceptible-exposed-infected-recovered model was used to simulate influenza transmission in low and high incidence seasons for two scenarios: 1. QIVe for 6 months-17 year-olds, QIVc for 18-64 year-olds, and adjuvanted QIV (aQIV) for ≥ 65 year-olds, and 2. QIVc for 6 months-64 year-olds, and aQIV for ≥ 65 year-olds. Probabilistic sensitivity analysis was performed to account for uncertainty in parameter estimates. Cost-effectiveness was evaluated as incremental cost-effectiveness ratios (ICERs).

RESULTS

Extension of QIVc to children resulted in 3-4% reductions in cases (1,656,271), hospitalizations (16,688), and deaths (2,126) at a population level in a high incidence season, and 65% reductions (cases: 2,856,384; hospitalizations: 31667; deaths: 4,163) in a low incidence season. Use of QIVc would be cost-saving, with ICERs of -$16,427/QALY and -$8,100/QALY from a payer perspective and -$22,669/QALY and -$15,015/QALY from a societal perspective, for low and high incidence seasons respectively. Cost savings were estimated at approximately $468 million and $1.366 billion for high and low incidence seasons, respectively.

CONCLUSION

Use of QIVc instead of QIVe in children > 6 months of age in the US would reduce the disease burden and be cost-saving from both a payer and societal perspective.

Influenza burden averted with a cell-based quadrivalent seasonal influenza vaccine compared with egg-based quadrivalent seasonal influenza vaccine

BACKGROUND

Cell-based quadrivalent inactivated influenza vaccines (IIV4c) avoid egg-adaptive mutations found in egg-based production, improving vaccine effectiveness (VE). Studies demonstrate improved VE for IIV4c relative to egg-based quadrivalent inactivated influenza vaccines (IIV4).

RESEARCH DESIGN AND METHODS

We built on a static compartmental model developed by the CDC to estimate the influenza burden in persons 0-64 years that would be additionally averted by vaccination with IIV4c vs. IIV4. Model inputs were based on published data from 2017-2018, 2018-2019, and 2019-2020 Northern Hemisphere influenza seasons for the US.

RESULTS

Over 3 influenza seasons, relative to IIV4, IIV4c would avert 31-39% more symptomatic cases, 29-40% more outpatient visits, 29-38% more hospitalizations and ICU admissions, and 34-49% more deaths vs. IIV4. In a deterministic sensitivity analysis, the main drivers were the relative VE of IIV4c vs. IIV4 in the 2017-2018 season and influenza burden estimates for the 2018-2019 and 2019-2020 seasons. Probabilistic sensitivity analysis showed that the interquartile range of symptomatic cases was ± 13% of baseline in 2017-2018, ±8% in 2018-2019, and ± 7% in 2019-2020.

CONCLUSIONS

IIV4c prevented significantly more symptomatic cases, outpatient visits, hospitalizations, and deaths than IIV4 in persons aged 0-64 years over 3 influenza seasons.

Cost-effectiveness of cell-based influenza vaccine in France

OBJECTIVES

Annually in France, influenza results in over one million GP consultations, around 20,000 hospitalizations, and approximately 9,000 deaths. This study assesses the cost-effectiveness of cell-based quadrivalent influenza vaccine (QIVc) for those under 65, which enhances effectiveness avoiding egg-adaptation, compared to egg-based quadrivalent influenza vaccine (QIVe).

METHODS

An age-structured susceptible-exposed-infected-recovered (SEIR) transmission model, calibrated to represent an average influenza season based on French data from 2011 to 2019, integrates a contact matrix estimating intergroup contact rates. Evaluating epidemiological, economic and utility outcomes, the model includes vaccine effectiveness and medical costs from the existing literature and French national data. Adjustments to quality of life due to infection and hospitalization are also included. Uncertainty is explored through scenario and sensitivity analyses.

RESULTS

Compared to QIVe, QIVc significantly reduces healthcare utilization and mortality, preventing 49,946 GP consultations, 1,087 hospitalizations, and 231 deaths in France. Despite an initial investment of 7.6 million euros, QIVc achieves a net saving of 12 million euros in healthcare expenditures, making it a dominant cost-saving strategy. Probabilistic sensitivity analyses indicate dominance in 78% of 10,000 simulations.

CONCLUSIONS

Introducing cell-based influenza vaccines in the French immunization program prevents influenza cases, hospitalizations, death, while reducing costs versus egg-based influenza vaccines.

Vaccine Effectiveness of Cell-Based Quadrivalent Influenza Vaccine in Children: A Narrative Review

Cell-based manufacturing of seasonal influenza vaccines eliminates the risk of egg-adaptation of candidate vaccine viruses, potentially increasing vaccine effectiveness (VE). We present an overview of published data reporting the VE and cost-effectiveness of a cell-based quadrivalent influenza vaccine (QIVc) in preventing influenza-related outcomes in the pediatric population. We identified 16 clinical studies that included data on the VE of a QIVc or the relative VE (rVE) of a QIVc versus an egg-based QIV (QIVe) in children and/or adolescents, 11 of which presented estimates specifically for the pediatric age group. Of these, two studies reported rVE against hospitalizations. Point estimates of rVE varied from 2.1% to 33.0%, with studies reporting significant benefits of using a QIVc against influenza-related, pneumonia, asthma, and all-cause hospitalization. Four studies reported rVE against influenza-related medical encounters, with point estimates against non-strain specific encounters ranging from 3.9% to 18.8% across seasons. One study evaluated rVE against any influenza, with variable results by strain. The other four studies presented VE data against laboratory-confirmed influenza. Three health economics studies focusing on a pediatric population also found the use of QIVc to be cost-effective or cost-saving. Overall, using a QIVc is effective in pediatric patients, with evidence of incremental benefits over using a QIVe in preventing hospitalizations and influenza-related medical encounters in nearly all published studies.

The burden of influenza and the role of influenza vaccination in adults aged 50-64 years: A summary of available evidence

Influenza is a vaccine-preventable disease and a global public health problem. Although most national influenza vaccination recommendations focus on subjects aged ≥65 years, an extensive burden of influenza has also been reported in those aged ≥50 years and is exacerbated by immune system aging. The main purpose of this review is to provide an overview of the burden of influenza and its potential prevention within the 50-64 age-group. These subjects account for a large proportion of the workforce, and play a central economic and social role. Individuals aged 50-64 years had a 3-times higher rate of hospitalization and a 9-fold higher mortality rate attributable to influenza than those aged 18-49-years, generating higher influenza-related hospitalization costs. Available data suggest that including healthy subjects aged 50-64 years in influenza vaccination recommendations would allow a broader population to be reached, reducing the economic and social burden of influenza.

Development of MDCK-based quadrivalent split seasonal influenza virus vaccine with high safety and immunoprotection: A preclinical study

Vaccination remains the best prevention strategy against influenza. The MDCK-based influenza vaccine prompted the development of innovative cell culture manufacturing processes. In the present study, we report the effects of multiple administrations of a candidate, seasonal, MDCK-based, quadrivalent split influenza virus vaccine MDCK-QIV in Sprague-Dawley (SD) rats. Moreover, the effects of the vaccine were evaluated in terms of fertility and early embryonic development, embryo-fetal development, and perinatal toxicity in the SD rats and immunogenicity in Wistar rats and BALB/c mice. Regarding the safety profile, MDCK-QIV demonstrated tolerance in local stimulation with repeated dose administration and presented no significant effect on the development, growth, behavior, fertility, and reproductive performance of the adult male rats, maternal rats, and their offspring. MDCK-QIV elicited strong hemagglutination inhibition neutralizing antibody response and protection against the influenza virus in the mouse model. Thus, data supported that MDCK-QIV could be further evaluated in human clinical trial, which is currently underway.

Moderately Low Effectiveness of the Influenza Quadrivalent Vaccine: Potential Mismatch between Circulating Strains and Vaccine Strains

The annual seasonal influenza vaccination is the most effective way of preventing influenza illness and hospitalization. However, the effectiveness of influenza vaccines has always been controversial. Therefore, we investigated the ability of the quadrivalent influenza vaccine to induce effective protection. Here we report strain-specific influenza vaccine effectiveness (VE) against laboratory-confirmed influenza cases during the 2019/2020 season, characterized by the co-circulation of four different influenza strains. During 2019-2020, 778 influenza-like illness (ILI) samples were collected from 302 (39%) vaccinated ILI patients and 476 (61%) unvaccinated ILI patients in Riyadh, Saudi Arabia. VE was found to be 28% and 22% for influenza A and B, respectively. VE for preventing A(H3N2) and A(H1N1)pdm09 illness was 37.4% (95% CI: 43.7-54.3) and 39.2% (95% CI: 21.1-28.9), respectively. The VE for preventing influenza B Victoria lineage illness was 71.7% (95% CI: -0.9-3), while the VE for the Yamagata lineage could not be estimated due to the limited number of positive cases. The overall vaccine effectiveness was moderately low at 39.7%. Phylogenetic analysis revealed that most of the Flu A genotypes in our dataset clustered together, indicating their close genetic relatedness. In the post-COVID-19 pandemic, flu B-positive cases have reached three-quarters of the total number of influenza-positive cases, indicating a nationwide flu B surge. The reasons for this phenomenon, if related to the quadrivalent flu VE, need to be explored. Annual monitoring and genetic characterization of circulating influenza viruses are important to support Influenza surveillance systems and to improve influenza vaccine effectiveness.

Estimating the Impact of Influenza Vaccination on Acute and ICU Hospital Bed Usage in an Influenza Season under Endemic COVID-19 in the US

In 2021–2022, influenza vaccine coverage in the US dropped below pre-COVID-19 pandemic levels. Cocirculation of COVID-19 and influenza could place a substantial burden on hospital utilization in future seasons, particularly given the reduced exposure to influenza during the pandemic. We used a dynamic susceptible-exposed-infected-recovered model to simulate influenza transmission with varying influenza vaccine coverage against a background of COVID-19 circulation, in order to estimate acute and ICU hospital bed occupancy for both diseases. We evaluated two vaccine scenarios: egg-based quadrivalent influenza vaccine (QIVe) for all age groups or cell-based QIV (QIVc) for 0.5–64 year-olds with adjuvanted QIV (aQIV) for ≥65 year-olds. ICU bed availability was more limiting than general hospital bed availability, with a vaccine coverage of ≥70% required to avoid negatively impacting ICU bed availability in a high-incidence influenza season. The timing of disease peaks was a key factor together with vaccine coverage, with a difference of ≥50 days needed between peak influenza and COVID-19 bed usage together with 65% influenza vaccine coverage to avoid negative impacts. QIVc + aQIV resulted in lower bed occupancy which, while not substantial, may be critical in very high hospital resource usage situations. In a situation with co-circulating influenza and COVID-19, proactive vaccination planning could help to avert overwhelming healthcare systems in upcoming influenza seasons.

[Aging of the immune system]

Mit zunehmendem Alter sind ein Anstieg der Inzidenz von Infektionen, inflammatorischen Erkrankungen, wie Arteriosklerose, und Tumoren sowie parallel eine Reduktion des Impferfolgs zu beobachten. Dafür ist ein dysfunktionelles Immunsystem verantwortlich. Das Immunsystem kann in 3 Bereiche eingeteilt werden. Die erste Barriere, die epitheloide Schutzschicht der Haut und der Schleimhäute, verliert mit dem Alter ihre Schutzfunktion. Die zweite Barriere, das angeborene Immunsystem, wird im Alter durch eine chronische niedriggradige Entzündung bei gleichzeitiger Reduktion einer adäquaten Antwort auf Pathogene charakterisiert. Die reduzierte Bildung neuer naiver Lymphozyten und eine Abnahme der Diversität kennzeichnen das adaptive Immunsystem, die dritte Barriere, im Alter. Diese als Immunseneszenz zusammengefassten Veränderungen sind für eine Vielzahl von degenerativen Erkrankungen mitverantwortlich.