Rationale for two influenza B lineages in seasonal vaccines: A meta-regression study on immunogenicity and controlled field trials

Immunogenicity and safety of inactivated quadrivalent influenza vaccine compared with the trivalent vaccine for influenza infection: an overview of systematic reviews

BACKGROUND

Influenza infection is a highly preventable transmissible viral disease associated with mild upper respiratory symptoms and more severe conditions such as lethal pneumonia. Studies have shown that a broader spectrum influenza vaccine could reduce influenza's burden of disease in low- and middle-income countries. A considerable number of systematic reviews reported that quadrivalent influenza vaccines are considered more effective compared to trivalent vaccines, hence, there is a need for an overview in order to synthesize the current evidence pertaining to the comparison between quadrivalent and trivalent inactivated influenza vaccines.

OBJECTIVE

The aim was to summarize the evidence from systematic reviews that investigated the immunogenicity and safety of the Influenza's inactivated quadrivalent vaccine (QIV) compared to the trivalent vaccine (TIV), in the general population.

METHODS

We searched articles up to December 2022 at: Web of Science, EMBASE, MEDLINE, Cochrane Library, and SCOPUS. The search strategy was conducted following the PICO model. We included systematic reviews comparing the primary outcomes of immunogenicity (seroprotection rate and seroconversion rate) and adverse events using risk ratios. The AMSTAR 2 and ROBIS were used for quality assessments, and GRADE was used for evidence certainty assessments.

FINDINGS

We included five systematic reviews, totalling 47,740 participants. The Quadrivalent Inactivated Influenza Vaccine (QIV) exhibited enhanced immunogenicity in the context of B-lineage mismatch when compared to the Trivalent Inactivated Influenza Vaccine (TIV). While the safety profile of QIV was found to be comparable to that of TIV, the QIV showed a higher incidence of solicited local pain among children and adolescents, as well as an increased frequency of local adverse events within the adult population.

CONCLUSION

Our findings suggest that the QIV provides a superior immunogenicity response compared to the TIV in all age groups evaluated, especially when a lineage mismatch occurred. The safety of QIV was considered similar to the TIV, with no serious or systemic solicited or unsolicited adverse events; tough pain at the injection site was greater for QIV. We recommend caution owing to the high risk of bias in the selection process and no protocol registration.

Return on Investment (ROI) of Three Vaccination Programmes in Italy: HPV at 12 Years, Herpes Zoster in Adults, and Influenza in the Elderly

The calculation of the return on investment (ROI) allows the estimation of the opportunity cost of a series of interventions and can therefore help to make allocative choices. The objective of this study is to estimate the ROI of three vaccinations (HPV for adolescents, HZ for adults, and influenza for the elderly) in the Italian context, considering the impact of increasing vaccination coverage based on target objectives of the National Immunization Plan (PNPV) 2017-2019 and accounting for different eligibility criteria of each vaccination. Three separate static cohort models were constructed, including the eligible population for these vaccinations on the basis of the PNPV 2017-2019 and following this population until death (lifetime horizon) or until vaccination waning. Each model compares the level of investment at current vaccine coverage rates (current VCRs scenario) with that of optimal NIP target VCRs with a non-vaccination scenario. The ROI for HPV vaccination was the highest among the programs compared and was always above 1 (range: 1.4-3.58), while lower values were estimated for influenza vaccination in the elderly (range 0.48-0.53) and for vaccination against HZ (range: 0.09-0.27). Our analysis showed that a significant proportion of savings generated by vaccination programs occurred outside the NHS perspective and might often not be estimated with other forms of economic evaluation.

Relative effectiveness of the adjuvanted vs non-adjuvanted seasonal influenza vaccines against severe laboratory-confirmed influenza among hospitalized Italian older adults

OBJECTIVES

In this study, we aimed to investigate the relative vaccine effectiveness (rVE) of the MF59-adjuvanted trivalent (aTIV) and non-adjuvanted quadrivalent (QIVe) egg-based standard-dose vaccines against severe laboratory-confirmed influenza.

METHODS

This test-negative case-control study was conducted in a hospital setting during four recent Italian influenza seasons (from 2018/19 to 2021/22). The clinical outcome was severe acute respiratory infection (SARI) with laboratory confirmation diagnosed among subjects aged ≥65 years. rVE of aTIV versus QIVe was estimated through propensity score matching followed by logistic regression.

RESULTS

The influenza virus circulated to a significant extent only during the 2018/19 and 2019/20 seasons. The final population included 512 vaccinated older adults, of which 83 were cases and 429 were test-negative controls. aTIV and QIVe users differed substantially from the point of view of several baseline characteristics. The propensity score adjusted rVE of aTIV vs QIVe was 59.2% (95% CI: 14.6%, 80.5%), 54.7% (95% CI: -28.7%, 84.0%) and 56.9% (95% CI: -7.8%, 82.8%) against any influenza, A(H1N1)pdm09 and A(H3N2), respectively.

CONCLUSION

aTIV was more effective than QIVe in preventing laboratory-confirmed SARI. The benefits of aTIV may be obscured by confounding indication.

Adjuvanted versus non-adjuvanted standard-dose influenza vaccines in preventing all-cause hospitalizations in the elderly: a cohort study with nested case-control analyses over 18 influenza seasons

BACKGROUND

The higher effectiveness of adjuvanted trivalent influenza vaccine (aTIV) versus non-adjuvanted (na) formulations in preventing all-cause hospitalization has been demonstrated for a single influenza season and in institutionalized elderly only. This study evaluated the relative vaccine effectiveness for aTIV vs. non-adjuvanted trivalent (naTIV) and/or quadrivalent (naQIV) influenza vaccines in preventing all-cause hospitalizations across 18 influenza seasons in primary care.

RESEARCH DESIGN AND METHODS

Using Health Search Database, a nested case-control analysis was conducted in a cohort of older adults being vaccinated with aTIV or naTIV/naQIV. Conditional logistic regression was adopted to estimate the odds ratio (OR) of all-cause hospitalizations occurred during the epidemic period.

RESULTS

Of 58,252 patients vaccinated with aTIV and naTIV/naQIV for the first time, 2,504 cases of all-cause hospitalization (3.46 per 1,000 person-weeks) during the 18 influenza seasons were identified. Compared with naTIV/naQIV, aTIV was associated with a 12% reduced the odds of all-cause hospitalizations (OR 0.88; 95% CI: 0.80-0.98).

CONCLUSIONS

In an 18-season cohort of older adults, aTIV reduced the risk of all-cause hospitalizations when compared with naTIV/naQIV. Our findings confirm additional benefits for adjuvanted influenza vaccines in older adults.

Influenza B Lineages Have More in Common Than Meets the Eye. Trivalent Influenza Vaccines Trigger Heterotypic Antibodies Against Both Influenza B Viruses

Influenza B is accountable for an important burden during flu epidemics, causing special impact in children and the elderly. Vaccination is the best approach to address influenza infections. However, one of the main problems of this virus is that two different lineages circulate together, Victoria and Yamagata; and trivalent vaccines, that only contain one of these lineages, are still in use. For that reason, if during an epidemic, the lineage not included in the vaccine predominates, a mismatch would occur, and the vaccine effectiveness will be very poor. In this work, we evaluated the cross-protection given by the trivalent Influenza vaccine and compared serological profiles based on age, sex, and the type of vaccine used. We performed a retrospective analysis of serum samples obtained before and after seasonal influenza vaccination during 20 seasons (1998–2018). The results showed that heterotypic reactivity between both influenza B lineages is common, but always lower than the homologous response. Age is a relevant factor for this cross-reactivity between both lineages, while the sex and the type of vaccine not. Vaccination with trivalent influenza vaccines elicits cross-reactive antibodies against both lineages, however, this response might not be enough to provide an appropriate serological protection in case of mismatch.

Mosaic Hemagglutinin-Based Whole Inactivated Virus Vaccines Induce Broad Protection Against Influenza B Virus Challenge in Mice

Influenza viruses undergo antigenic changes in the immuno-dominant hemagglutinin (HA) head domain, necessitating annual re-formulation of and re-vaccination with seasonal influenza virus vaccines for continuing protection. We previously synthesized mosaic HA (mHA) proteins of influenza B viruses which redirect the immune response towards the immuno-subdominant conserved epitopes of the HA via sequential immunization. As ~90% of current influenza virus vaccines are manufactured using the inactivated virus platform, we generated and sequentially vaccinated mice with inactivated influenza B viruses displaying either the homologous (same B HA backbones) or the heterologous (different B HA backbones) mosaic HAs. Both approaches induced long-lasting and cross-protective antibody responses showing strong antibody-dependent cellular cytotoxicity (ADCC) activity. We believe the B virus mHA vaccine candidates represent a major step towards a universal influenza B virus vaccine.

Influenza Vaccines: Successes and Continuing Challenges

Influenza vaccines have been available for over 80 years. They have contributed to significant reductions in influenza morbidity and mortality. However, there have been limitations in their effectiveness, in part due to the continuous antigenic evolution of seasonal influenza viruses, but also due to the predominant use of embryonated chicken eggs for their production. The latter furthermore limits their worldwide production timelines and scale. Therefore today, alternative approaches for their design and production are increasingly pursued, with already licensed quadrivalent seasonal influenza vaccines produced in cell cultures, including based on a baculovirus expression system. Next-generation influenza vaccines aim at inducing broader and longer-lasting immune responses to overcome seasonal influenza virus antigenic drift and to timely address the emergence of a new pandemic influenza virus. Tailored approaches target mechanisms to improve vaccine-induced immune responses in individuals with a weakened immune system, in particular older adults.

Effect of High-Dose Trivalent vs Standard-Dose Quadrivalent Influenza Vaccine on Mortality or Cardiopulmonary Hospitalization in Patients With High-risk Cardiovascular Disease: A Randomized Clinical Trial

IMPORTANCE

Influenza is temporally associated with cardiopulmonary morbidity and mortality among those with cardiovascular disease who may mount a less vigorous immune response to vaccination. Higher influenza vaccine dose has been associated with reduced risk of influenza illness.

OBJECTIVE

To evaluate whether high-dose trivalent influenza vaccine compared with standard-dose quadrivalent influenza vaccine would reduce all-cause death or cardiopulmonary hospitalization in high-risk patients with cardiovascular disease.

DESIGN, SETTING, AND PARTICIPANTS

Pragmatic multicenter, double-blind, active comparator randomized clinical trial conducted in 5260 participants vaccinated for up to 3 influenza seasons in 157 sites in the US and Canada between September 21, 2016, and January 31, 2019. Patients with a recent acute myocardial infarction or heart failure hospitalization and at least 1 additional risk factor were eligible.

INTERVENTIONS

Participants were randomly assigned to receive high-dose trivalent (n = 2630) or standard-dose quadrivalent (n = 2630) inactivated influenza vaccine and could be revaccinated for up to 3 seasons.

MAIN OUTCOMES AND MEASURES

The primary outcome was the time to the composite of all-cause death or cardiopulmonary hospitalization during each enrolling season. The final date of follow-up was July 31, 2019. Vaccine-related adverse events were also assessed.

RESULTS

Among 5260 randomized participants (mean [SD] age, 65.5 [12.6] years; 3787 [72%] men; 3289 [63%] with heart failure) over 3 influenza seasons, there were 7154 total vaccinations administered and 5226 (99.4%) participants completed the trial. In the high-dose trivalent vaccine group, there were 975 primary outcome events (883 hospitalizations for cardiovascular or pulmonary causes and 92 deaths from any cause) among 884 participants during 3577 participant-seasons (event rate, 45 per 100 patient-years), whereas in the standard-dose quadrivalent vaccine group, there were 924 primary outcome events (846 hospitalizations for cardiovascular or pulmonary causes and 78 deaths from any cause) among 837 participants during 3577 participant-seasons (event rate, 42 per 100 patient-years) (hazard ratio, 1.06 [95% CI, 0.97-1.17]; P = .21). In the high-dose vs standard-dose groups, vaccine-related adverse reactions occurred in 1449 (40.5%) vs 1229 (34.4%) participants and severe adverse reactions occurred in 55 (2.1%) vs 44 (1.7%) participants.

CONCLUSIONS AND RELEVANCE

In patients with high-risk cardiovascular disease, high-dose trivalent inactivated influenza vaccine, compared with standard-dose quadrivalent inactivated influenza vaccine, did not significantly reduce all-cause mortality or cardiopulmonary hospitalizations. Influenza vaccination remains strongly recommended in this population.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02787044.

Immunogenicity and safety of a quadrivalent inactivated influenza vaccine in healthy subjects aged 3 to 17 years old: A phase III, open label, single-arm study

BACKGROUND

Quadrivalent influenza vaccines are particularly valuable during seasons in which a mismatch occurs between the predicted influenza B lineage for the trivalent influenza vaccine and the circulating strain. This study evaluated the immunogenicity and safety of a quadrivalent inactivated influenza vaccine AdimFlu-S manufactured in Taiwan for the 2016-2017 influenza season in healthy children.

METHODS

A total of 174 healthy children aged 3 to 17 years old were separated into 3 groups (Group A: 3-8 years old, vaccine naïve; Group B: 3-8 years old, vaccine non-naïve; Group C: 9-17 years old, any vaccine status). Sera was collected pre and post vaccination for each participant. A hemagglutination inhibition (HAI) assay was utilized to calculate geometric mean titer (GMT), seroprotection rate, and seroconversion rate.

RESULTS

All enrolled participants completed the study. For the four vaccine strains four weeks after the last vaccination, geometric mean titer ratios (GMTRs) were between 2.9 and 20.9, seroconversion rates were between 42.9% and 90.9%, and seroprotection rates were all above 96.4%. This achieved all immunogenicity endpoints and fulfilled the criteria of the European Medical Agency's Committee for Medicinal Products for Human Use (CHMP). No serious adverse events (AEs) were reported during the follow-up period of 6 months.

CONCLUSION

This quadrivalent influenza vaccine is demonstrated to be well tolerated and displays robust immunogenicity for each influenza strain. This could potentially improve protection against the antigenically distinct B/Yamagata and B/Victoria lineages.

Influenza vaccine effectiveness against hospitalization with laboratory-confirmed influenza in Greece: A pooled analysis across six seasons, 2013-2014 to 2018-2019

BACKGROUND

Monitoring seasonal influenza Vaccine Effectiveness (VE) is key to inform vaccination strategies and sustain uptake. Pooling data across multiple seasons increases precision and allows for subgroup analyses, providing more conclusive evidence. Our aim was to assess VE against hospitalization with laboratory-confirmed influenza in Greece over six seasons, from 2013 to 2014 to 2018-2019, using routinely collected surveillance data.

METHODS

Swab samples from hospitalized patients across the country were tested for influenza by RT-PCR. We used the test-negative design, with patients testing positive for influenza serving as cases and those testing negative serving as controls. VE was calculated as one minus the Odds Ratio (OR) for influenza vaccination, estimated by mixed-effects logistic regression and adjusted for age, sex, hospitalization type (being in intensive care or not), time from symptom onset to swabbing, and calendar time. Stratified estimates by age and hospitalization type were obtained, and also subgroup estimates by influenza type/subtype and season. Antigenic and genetic characterization of a subset of circulating influenza strains was performed.

RESULTS

A total of 3,882 test-positive cases and 5,895 test-negative controls were analyzed. Across all seasons, adjusted VE was 45.5% (95% CI: 31.6-56.6) against all influenza, 62.8% against A(H1N1)pdm09 (95% CI: 40.7-76.7), 28.2% against A(H3N2) (95% CI: 12.0-41.3) and 45.5% against influenza B (95% CI: 29.1-58.1). VE was slightly lower for patients aged 60 years and over, and similar between patients hospitalized inside or outside intensive care. Circulating A(H1N1)pdm09 and B strains were antigenically similar to the vaccine strains, whereas A(H3N2) were not.

CONCLUSION

Our results confirm the public health benefits from seasonal influenza vaccination, despite the suboptimal effectiveness against A(H3N2) strains. Continued monitoring of VE is essential, and routinely collected surveillance data can be valuable in this regard.

Association between vaccine adjuvant effect and pre-seasonal immunity. Systematic review and meta-analysis of randomised immunogenicity trials comparing squalene-adjuvanted and aqueous inactivated influenza vaccines

The immunogenicity benefit of inactivated influenza vaccine (IIV) adjuvanted by squalene over non-adjuvanted aqueous IIV was explored in a meta-analysis involving 49 randomised trials published between 1999 and 2017, and 22,470 eligible persons of all age classes. Most vaccines contained 15 μg viral haemagglutinin per strain. Adjuvanted IIV mostly contained 9.75 mg squalene per dose. Homologous pre- and post-vaccination geometric mean titres (GMTs) of haemagglutination-inhibition (HI) antibody were recorded for 290 single influenza (sub-)type arms. The adjuvant effect was expressed as the ratio of post-vaccination GMTs between squalene-IIV and aqueous IIV (GMTR, 145 estimates). GMTRs > 1.0 favoured squalene-IIV over aqueous IIV. For all influenza (sub-)types, the adjuvant effect proved negatively associated with pre-vaccination GMT and mean age. The adjuvant effect appeared most pronounced in young children (mean age < 2.5 years) showing an average GMTR of 3.7 (95% CI: 2.5 to 5.5). With increasing age, GMTR values gradually decreased towards 1.4 (95% CI: 1.0 to 1.9) in older adults. Heterologous antibody titrations simulating mismatch between vaccine and circulating virus (30 GMTR estimates) again showed a larger adjuvant effect at young age. GMT values and their variances were converted to antibody-predicted protection rates using an evidence-based clinical protection curve. The adjuvant effect was expressed as the protection rate differences, which showed similar age patterns as corresponding GMTR values. However for influenza B, the adjuvant effect lasted longer than for influenza A, possibly due to a generally later influenza B virus exposure. Collectively, this meta-analysis indicates the highest benefit of squalene-IIV over aqueous IIV in young children and decreasing benefit with progressing age. This trend is similar for seasonal influenza (sub-)types and the 2009 pandemic strain, by both homologous and heterologous titration. The impact of pre-seasonal immunity on vaccine effectiveness, and its implications for age-specific vaccination recommendations, are discussed.

Evaluation of Waning Immunity at 6 Months after Both Trivalent and Quadrivalent Influenza Vaccination in Korean Children Aged 6-35 Months

BACKGROUND

The titer of influenza vaccine-induced antibodies declines over time, and younger children have lower immunogenicity and shorter duration of immunity. This study aimed to compare persistence of antibody at 6 months after influenza vaccination according to influenza virus strains, vaccine type, antigen dose, and primed status in children aged 6 to 35 months.

METHODS

A total 124 healthy children aged 6 to 35 months were enrolled from September to December 2016 at 10 hospitals in Korea and randomly assigned to either a full dose of quadrivalent influenza vaccine or a half dose of trivalent influenza vaccine with Victoria B strain group. Hemagglutination inhibition antibody titers (that measure the seroprotection rates) were assessed for the recommended influenza strains at 6 months post vaccination.

RESULTS

The seroprotection rates at 6 months for strains A (H1N1), A (H3N2), B/Yamagata, and B/Victoria were 88.7%, 97.4%, 36.6%, and 27.6%, respectively. The seroprotection rates for A (H1N1), A (H3N2) and B (Victoria) were 91.4%, 98.7% and 27.5% in a full dose of quadrivalent vaccine vs. 83.7%, 94.6% and 27.9% in a half dose trivalent vaccine, respectively. The seroprotection rate for the B (Yamagata) strain was 23.8% in the quadrivalent group and 14.0% in the trivalent group.

CONCLUSION

Persistence of antibodies at 6 months was more favorable against the influenza A strains than against the B strains. Persistence of antibodies to additional B strain at 6 months was superior in the quadrivalent vaccine group. The immunity of primed children with different B strains was not superior to that of the unprimed group with another B strain.

Adjuvanted influenza vaccine for the Italian elderly in the 2018/19 season: an updated health technology assessment

BACKGROUND

The elderly, defined here as subjects aged ≥ 65 years, are among at-risk subjects for whom annual influenza vaccination is recommended. For the 2018/19 season, three vaccine types are available for the elderly in Italy: trivalent inactivated vaccine (TIV), adjuvanted TIV (aTIV) and quadrivalent inactivated vaccines (QIV). No health technology assessment (HTA) of seasonal influenza vaccination in the elderly has previously been conducted in Italy.

METHODS

An HTA was conducted in 2017 to analyze the burden of influenza illness, the characteristics, efficacy, safety and cost-effectiveness of available vaccines and the related organizational and ethical implications. This was then contextualized to the 2018/19 influenza season. Comprehensive literature reviews/analyses were performed and a static mathematical model developed in order to address the above issues.

RESULTS

In Italy, influenza is usually less common in the elderly than in other age-classes, but the burden of disease is the highest; >10% of infected elderly subjects develop complications, and about 90% of all influenza-related deaths occur in this age-class. All available vaccines are effective, safe and acceptable from an ethical standpoint. However, aTIV has proved more immunogenic and effective in the elderly. Furthermore, from the third payer's perspective, aTIV is highly cost-effective and cost-saving in comparison with TIV and QIV, respectively. Nevertheless, vaccination coverage needs to be improved.

CONCLUSIONS

According to this HTA, aTIV appeared the vaccine of choice in the elderly. HTA should be reapplied whenever new relevant data become available.

Comparative epidemiology of influenza B by lineage in intensive care unit-admitted patients with complications: A nationwide study in Taiwan, 2013-2017

BACKGROUND

We describe the relative proportions and epidemiological features of influenza B/Victoria and B/Yamagata, using data from nationwide surveillance systems.

METHODS

We collected respiratory samples from outpatients with influenza-like illness (ILI) and intensive care unit (ICU)-admitted patients with complications (pulmonary or neurological complications, myocarditis/pericarditis or invasive bacterial infection) for virus isolation and lineage typing. Demographics, epidemiological features, and vaccination history from ICU-admitted patients with complications were analyzed.

RESULTS

From July 2013-June 2017, 21% of 11517 influenza isolates were influenza B. B/Victoria was the predominant circulating strain in 2013-2014, accounted for 56% of all influenza B positive samples and B/Yamagata was predominant in 2014-2017 (82%, 69%, and 85%, respectively). Among all typed viruses, the proportion of B/Yamagata was higher among specimens from ICU-admitted patients with complications (77%, 154/199) than from ILI outpatients (66%, 276/418, p<0.005). Compared to B/Victoria, B/Yamagata infected ICU-admitted patients with complications were older, median age (71 vs. 59 years, p<0.05), had longer durations of hospitalization (15 vs. 7.5 days, p<0.05) and ICU stays (8.5 vs. 5.5 days, p<0.05).

CONCLUSIONS

Two lineages of influenza B viruses co-circulate annually in Taiwan. Among ICU-admitted patients with complications, B/Yamagata causes more severe illness than B/Victoria.

Effectiveness of the trivalent MF59 adjuvated influenza vaccine in preventing hospitalization due to influenza B and A(H1N1)pdm09 viruses in the elderly in Italy, 2017 - 2018 season

Background: Evidence on influenza vaccine effectiveness (VE) in preventing mortality and morbidity in the elderly is weak. Our aim was to measure the VE against severe outcomes in the elderly. Methods: We conducted a multicentre hospital-based test-negative design (TND) case-control study, during the 2017/18 season, in four Italian hospitals. The study population included individuals aged ≥65 years hospitalized with Severe Acute Respiratory Infections (SARI). Patients were classified as cases and controls based on the results of the PCR influenza testing. We estimated VE by virus subtypes and specific VE for the trivalent adjuvanted vaccine (TIVadj). Results: 502 patients with SARI were enrolled: 118 (23.5%) tested positive (cases) and 384 (76.5%) tested negative (controls) for influenza. The adjusted VE of 48.5% for all vaccines was comparable to the adjusted VE for the TIVadj vaccine (48.3%). Adjusted VE for the TIVadj vaccine was 67.5% for A(H1N1)pdm09 and 44.5% for B viruses. Conclusion: We show a moderate adjusted VE of the TIVadj against all viruses, a good adjusted VE against A(H1N1)pdm09 strains and a moderate adjusted VE against B strains, despite a mismatch between the B circulating lineage and the lineage included in the vaccine. This is likely due to the cross-protection among B strains induced by the TIVadj in elderly patients.

Adjuvanted versus nonadjuvanted influenza vaccines and risk of hospitalizations for pneumonia and cerebro/cardiovascular events in the elderly

Background: The higher effectiveness of MF59®-adjuvanted trivalent influenza vaccine (MF59-TIV) vs. nonadjuvanted TIV in preventing influenza-related hospitalizations was found considering few influenza seasons, local and heterogeneous settings. This study evaluated the relative vaccine effectiveness (rVE) of MF59-TIV vs. nonadjuvanted TIV on the risk of hospitalization for pneumonia and cerebro/cardiovascular events across 15 consecutive influenza seasons. Research design and methods: Using Health Search Database, a case-control study was nested in a cohort of elderly vaccinated with MF59-TIV or TIV. Conditional logistic regression was used to estimate the odds ratio with 95% confidence intervals (CI) of hospitalizations potentially related to influenza in patients vaccinated with MF59-TIV or TIV. Results: Of 43,000 patients vaccinated with MF59-TIV (66.2%) and TIV (33.8%) for the first time, 103 cases of hospitalization for pneumonia or cerebro/cardiovascular events (0.11 per 1,000 person-weeks) during 15 influenza seasons were identified. The MF59-TIV was associated with a reduced risk of hospitalizations for pneumonia and cerebro/cardiovascular events vs. TIV [rVE: 39% (95% CI: 4-61%)]. Conclusions: In a 15-season cohort of elderly, MF59-TIV seems to reduce the risk of hospitalizations for pneumonia and cerebro/cardiovascular events when compared with nonadjuvanted TIV. Our findings support the recommendation for MF59-TIV in the elderly population.

Development of Influenza B Universal Vaccine Candidates Using the "Mosaic" Hemagglutinin Approach

Influenza B viruses cause seasonal epidemics and are a considerable burden to public health. However, protection by current seasonal vaccines is suboptimal due to the antigenic changes of the circulating strains. In this study, we report a novel universal influenza B virus vaccination strategy based on "mosaic" hemagglutinins. We generated mosaic B hemagglutinins by replacing the major antigenic sites of the type B hemagglutinin with corresponding sequences from exotic influenza A hemagglutinins and expressed them as soluble trimeric proteins. Sequential vaccination with recombinant mosaic B hemagglutinin proteins conferred cross-protection against both homologous and heterologous influenza B virus strains in the mouse model. Of note, we rescued recombinant influenza B viruses expressing mosaic B hemagglutinins, which could serve as the basis for a universal influenza B virus vaccine.IMPORTANCE This work reports a universal influenza B virus vaccination strategy based on focusing antibody responses to conserved head and stalk epitopes of the hemagglutinin. Recombinant mosaic influenza B hemagglutinin proteins and recombinant viruses have been generated as novel vaccine candidates. This vaccine strategy provided broad cross-protection in the mouse model. Our findings will inform and drive development toward a more effective influenza B virus vaccine.

Use of adjuvanted trivalent influenza vaccine in older-age adults: a systematic review of economic evidence

Seasonal influenza is a very common disease. Yearly vaccination of at-risk population groups is a well-recognized cost-effective/cost-saving preventive measure. It is, however, unclear which available alternative has the most favorable economic profile. Some available options are: trivalent (TIV) and quadrivalent (QIV) inactivated vaccines, adjuvanted TIV (aTIV). Because of immunosenescence, aTIV has been specifically developed for elderly. The present study aimed at assessing the available evidence of aTIV use in elderly from the economic perspective. A systematic literature review targeting aTIV economic evaluations in adults aged ≥65 years was performed using Medline via Ovid, Embase, DARE and NHS/EED. Of a total of 3,654 papers screened, 18 studies (13 full papers, 5 conference abstracts) were included. It emerged that compared with both non-vaccination or non-adjuvanted vaccines, aTIV was cost-effective or cost-saving. The vaccinations strategies incorporating aTIV based on age and/or risk profile are associated with the most favorable economic outcomes.

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.

Seasonal influenza immunisation: Strategies for older adults

Adults over the age of 60-65 years suffer disproportionally from seasonal influenza, experiencing high rates of complications, exacerbation of underlying medical comorbidities, and excess mortality. Thus, older adults are an important priority for influenza immunisation campaigns. Unfortunately, older adults generally display lower immune responses to standard influenza vaccines because of immunosenescence, with resulting suboptimal vaccine effectiveness. Thus, the development of improved vaccines that heighten immune responses and improve effectiveness is an important medical need. To this end, enhanced influenza vaccines specifically targeting this age group have been developed, which seek to overcome the inherent limitations in the immune responses of older adults. Both the licensed high-dose trivalent influenza vaccine (hdTIV) containing fourfold higher antigen contents than standard vaccine, and the MF59^® -adjuvanted trivalent influenza vaccine (aTIV) have been proven to be safe and well-tolerated while enhancing the immune response. Healthcare providers for populations of older adults should be advised to routinely use these enhanced influenza vaccines in seasonal immunisation campaigns to provide improved immunity against influenza and its consequences in this particularly susceptible age group.

[Seasonal flu vaccination for older people: Evaluation of the quadrivalent vaccine. Positioning report]

Influenza is a significant health problem, particularly in those persons susceptible to having associated complications, older people, children less than 2 years, patients with chronic diseases, immunocompromised patients, and pregnant women. But influenza also has a large impact on the health system, with an increase in the healthcare demand and a spectacular increase in outpatient visits, overloading the emergency and hospital services. During epidemic outbreaks, the hospital admission rates of people over 65 years are at a maximum, and the mortality notified for the 2017/2018 influenza season was 960 deaths. The seasonal anti-influenza vaccine is the method with a better cost-effective ratio of primary prevention of influenza, reducing associated respiratory diseases, the number of hospital admissions, and deaths in high risk individuals, as well as work absenteeism in adults. In the last few years, influenza B has received little attention in the scientific literature, although in the periods between epidemics influenza B can be one of the main causes of seasonal epidemics, causing considerable morbidity and mortality and an increase in costs. The quadrivalent vaccine has a second-line immunological protection against influenza B, and according to a critical review of the scientific literature, it provides wider protection without affecting immunogenicity of the other three vaccine strains common to the trivalent and tetravalent vaccine. The quadrivalent vaccine is cost-effective in reducing the number of influenza cases, and is always a worthwhile intervention, with a significant cost saving for the health system and for society, by reducing the hospital admission rates and mortality associated with the complications of influenza. Supplement information: This article is part of a supplement entitled 'Seasonal flu vaccination for older people: Evaluation of the quadrivalent vaccine' which is sponsored by Sanofi-Aventis, S.A.

The Effects of Birth Year, Age and Sex on Hemagglutination Inhibition Antibody Responses to Influenza Vaccination

The first exposure to influenza is thought to impact subsequent immune responses later in life. The consequences of this can be seen during influenza epidemics and pandemics with differences in morbidity and mortality for different birth cohorts. There is a need for better understanding of how vaccine responses are affected by early exposures to influenza viruses. In this analysis of hemagglutination inhibition (HI) antibody responses in two cohorts of military personnel we noticed differences related to age, sex, prior vaccination, deployment and birth year. These data suggest that HI antibody production, in response to influenza vaccination, is affected by these factors. The magnitude of this antibody response is associated with, among other factors, the influenza strain that circulated following birth.

Heterogeneous estimates of influenza virus types A and B in the elderly: Results of a meta-regression analysis

Influenza has many age‐dependent characteristics. A previous systematic review of randomized controlled trials showed that the detection rate of influenza B was higher in children than in non‐elderly adults. However, no comprehensive reviews have targeted the elderly, who carry the main burden of disease. We aimed to quantify the relative detection rates of virus types A and B among the elderly, to identify factors affecting these proportions, and to compare type distribution among seniors and younger age‐classes. A comprehensive literature search was conducted to identify multiseason studies reporting A and B virus type distributions in the elderly. A random‐effects meta‐analysis was planned to quantify the prevalence of type B among elderly subjects with laboratory‐confirmed influenza. Meta‐regression was then applied to explain the sources of heterogeneity. Across 27 estimates identified, the type B detection rate among seniors varied from 5% to 37%. Meta‐analysis was not feasible owing to high heterogeneity (I² = 98.5%). Meta‐regression analysis showed that study characteristics, such as number of seasons included, hemisphere, and setting, could have contributed to the heterogeneity observed. The final adjusted model showed that studies that included both outpatients and inpatients reported a significantly (P = .024) lower proportion than those involving outpatients only. The detection rate of type B among the elderly was generally lower than in children/adolescents, but not non‐elderly adults. Influenza virus type B has a relatively low detection rate in older adults, especially in settings covering both inpatients and outpatients. Public health implications are discussed.

Influenza vaccines: Evaluation of the safety profile

The safety of vaccines is a critical factor in maintaining public trust in national vaccination programs. Vaccines are recommended for children, adults and elderly subjects and have to meet higher safety standards, since they are administered to healthy subjects, mainly healthy children. Although vaccines are strictly monitored before authorization, the possibility of adverse events and/or rare adverse events cannot be totally eliminated. Two main types of influenza vaccines are currently available: parenteral inactivated influenza vaccines and intranasal live attenuated vaccines. Both display a good safety profile in adults and children. However, they can cause adverse events and/or rare adverse events, some of which are more prevalent in children, while others with a higher prevalence in adults. The aim of this review is to provide an overview of influenza vaccine safety according to target groups, vaccine types and production methods.

Cost-effectiveness analysis of different seasonal influenza vaccines in the elderly Italian population

In the perspective of reaching at least 75% influenza vaccination coverage in the elderly and substantial budget constraints, Italian decision makers are facing important challenges in determining an optimal immunization strategy for this growing and particularly vulnerable population. Four different influenza vaccines are currently available for Italian older adults aged 65 years or above, namely trivalent inactivated vaccines (TIVs), MF59-adjuvanted TIV (MF59-TIV), intradermal TIV (ID-TIV) and quadrivalent inactivated vaccines (QIVs). The present study is the first to compare the cost-effectiveness profiles of virtually all possible public health strategies, including the aforementioned four vaccine formulations as well non-vaccination. For this purpose, a decision tree model was built ex novo; the analysis was conducted from the third-payer perspective in the timeframe of one year. All available vaccines were cost-effective compared with non-vaccination. However, MF59-TIV had the most favorable economic profile in the Italian elderly population. Indeed, compared with non-vaccination, it was deemed highly cost-effective with an incremental cost-effectiveness ratio (ICER) of €10,750 per quality-adjusted life year (QALY). The ICER was much lower (€4,527/QALY) when MF59-TIV was directly compared with TIV. ID-TIV and QIV were dominated by MF59-TIV as the former comparators were associated with greater total costs and lower health benefits. Both deterministic and probabilistic sensitivity analyses confirmed robustness of the base case results. From the economic perspective, MF59-TIV should be considered as a preferential choice for Italian older adults aged 65 years or above.

Primary Human Influenza B Virus Infection Induces Cross-Lineage Hemagglutinin Stalk-Specific Antibodies Mediating Antibody-Dependent Cellular Cytoxicity

Influenza A virus (IAV) and influenza B virus (IBV) cause substantial morbidity and mortality during annual epidemics. Two distinct lineages of IBV are distinguished, based on variation in hemagglutinin (HA): B/Victoria/2/87-like (B/Vic) and B/Yamagata/16/88-like (B/Yam). Here, we show that, in humans, primary IBV infection with either lineage induces HA-specific antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies. IBV infection induced antibodies specific to the HA head and stalk, but only HA stalk-specific antibodies mediated ADCC efficiently and displayed cross-reactivity with IBV of both lineages. This corresponds to recent findings that 2 points of contact between the effector and target cell (ie, HA and sialic acid, respectively, and the fragment crystallizable [Fc] domain and Fcγ receptor IIIα, respectively) are required for efficient ADCC activity and that antibodies specific for the receptor-binding site located in the head domain of HA therefore fail to mediate ADCC. Potentially, ADCC-mediating antibodies directed to the HA stalk of IBV contribute to cross-protective immunity to IBV of both lineages.