Role of Egg-adaptation Mutations in Low Influenza A(H3N2) Vaccine Effectiveness During the 2012-2013 Season

Zoonosis and zooanthroponosis of emerging respiratory viruses

Lung infections in Influenza-Like Illness (ILI) are triggered by a variety of respiratory viruses. All human pandemics have been caused by the members of two major virus families, namely Orthomyxoviridae (influenza A viruses (IAVs); subtypes H1N1, H2N2, and H3N2) and Coronaviridae (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2). These viruses acquired some adaptive changes in a known intermediate host including domestic birds (IAVs) or unknown intermediate host (SARS-CoV-2) following transmission from their natural reservoirs (e.g. migratory birds or bats, respectively). Verily, these acquired adaptive substitutions facilitated crossing species barriers by these viruses to infect humans in a phenomenon that is known as zoonosis. Besides, these adaptive substitutions aided the variant strain to transmit horizontally to other contact non-human animal species including pets and wild animals (zooanthroponosis). Herein we discuss the main zoonotic and reverse-zoonosis events that occurred during the last two pandemics of influenza A/H1N1 and SARS-CoV-2. We also highlight the impact of interspecies transmission of these pandemic viruses on virus evolution and possible prophylactic and therapeutic interventions. Based on information available and presented in this review article, it is important to close monitoring viral zoonosis and viral reverse zoonosis of pandemic strains within a One-Health and One-World approach to mitigate their unforeseen risks, such as virus evolution and resistance to limited prophylactic and therapeutic interventions.

Antibody-mediated NK cell activation as a correlate of immunity against influenza infection

Antibodies play a critical role in protection against influenza; yet titers and viral neutralization represent incomplete correlates of immunity. Instead, the ability of antibodies to leverage the antiviral power of the innate immune system has been implicated in protection from and clearance of influenza infection. Here, post-hoc analysis of the humoral immune response to influenza is comprehensively profiled in a cohort of vaccinated older adults (65 + ) monitored for influenza infection during the 2012/2013 season in the United States (NCT: 01427309). While robust humoral immune responses arose against the vaccine and circulating strains, influenza-specific antibody effector profiles differed in individuals that later became infected with influenza, who are deficient in NK cell activating antibodies to both hemagglutinin and neuraminidase, compared to individuals who remained uninfected. Furthermore, NK cell activation was strongly associated with the NK cell senescence marker CD57, arguing for the need for selective induction of influenza-specific afucosylated NK activating antibodies in older adults to achieve protection. High dose vaccination, currently used for older adults, was insufficient to generate this NK cell-activating humoral response. Next generation vaccines able to selectively bolster NK cell activating antibodies may be required to achieve protection in the setting of progressively senescent NK cells.

Advances in Adjuvanted Influenza Vaccines

The numerous influenza infections that occur every year present a major public health problem. Influenza vaccines are important for the prevention of the disease; however, their effectiveness against infection can be suboptimal. Particularly in the elderly, immune induction can be insufficient, and the vaccine efficacy against infection is usually lower than that in young adults. Vaccine efficacy can be improved by the addition of adjuvants, and an influenza vaccine with an oil-in-water adjuvant MF59, FLUAD, has been recently licensed in the United States and other countries for persons aged 65 years and older. Although the adverse effects of adjuvanted vaccines have been a concern, many adverse effects of currently approved adjuvanted influenza vaccines are mild and acceptable, given the overriding benefits of the vaccine. Since sufficient immunity can be induced with a small amount of vaccine antigen in the presence of an adjuvant, adjuvanted vaccines promote dose sparing and the prompt preparation of vaccines for pandemic influenza. Adjuvants not only enhance the immune response to antigens but can also be effective against antigenically different viruses. In this narrative review, we provide an overview of influenza vaccines, both past and present, before presenting a discussion of adjuvanted influenza vaccines and their future.

Estimates of Inactivated Influenza Vaccine Effectiveness Among Children in Senegal: Results From 2 Consecutive Cluster-Randomized Controlled Trials in 2010 and 2011

BACKGROUND

We report results of years 2 and 3 of consecutive cluster-randomized controlled trials of trivalent inactivated influenza vaccine (IIV3) in Senegal.

METHODS

We cluster-randomized (1:1) 20 villages to annual vaccination with IIV3 or inactivated poliovirus vaccine (IPV) of age-eligible residents (6 months-10 years). The primary outcome was total vaccine effectiveness against laboratory-confirmed influenza illness (LCI) among age-eligible children (modified intention-to-treat population [mITT]). Secondary outcomes were indirect (herd protection) and population (overall community) vaccine effectiveness.

RESULTS

We vaccinated 74% of 12 408 age-eligible children in year 2 (June 2010-April 11) and 74% of 11 988 age-eligible children in year 3 (April 2011-December 2011) with study vaccines. Annual cumulative incidence of LCI was 4.7 (year 2) and 4.2 (year 3) per 100 mITT child vaccinees of IPV villages. In year 2, IIV3 matched circulating influenza strains. The total effectiveness was 52.8% (95% confidence interval [CI], 32.3-67.0), and the population effectiveness was 36.0% (95% CI, 10.2-54.4) against LCI caused by any influenza strain. The indirect effectiveness against LCI by A/H3N2 was 56.4% (95% CI, 39.0-68.9). In year 3, 74% of influenza detections were vaccine-mismatched to circulating B/Yamagata and 24% were vaccine-matched to circulating A/H3N2. The year 3 total effectiveness against LCI was -14.5% (95% CI, -81.2-27.6). Vaccine effectiveness varied by type/subtype of influenza in both years.

CONCLUSIONS

IIV3 was variably effective against influenza illness in Senegalese children, with total and indirect vaccine effectiveness present during the year when all circulating strains matched the IIV3 formulation.

CLINICAL TRIALS REGISTRATION

NCT00893906.

Phase III: Randomized observer-blind trial to evaluate lot-to-lot consistency of a new plant-derived quadrivalent virus like particle influenza vaccine in adults 18-49 years of age

BACKGROUND

The global reliance on eggs to produce most influenza vaccines has several limitations and new approaches to influenza vaccine production are needed. Herein we describe a phase 3, lot-to-lot consistency trial (NCT03321968) of a quadrivalent, recombinant, virus-like particle (VLP) influenza vaccine produced in plants. This platform is based on transient expression of proteins in Nicotiana benthamiana and yields VLPs bearing hemagglutinin (HA) protein trimers that are combined in a quadrivalent vaccine (QVLP).

METHODS

The HAs targeted in this study were A/California/07/2009 H1N1, A/Hong Kong/4801/2014 H3N2, B/Brisbane/60/08 and B/Phuket/3073/2013: recommended for the 2016-2017 Northern Hemisphere season. Healthy adults 18-49 years of age (n = 1200) were randomized 1:1:1 to receive a 0.5 mL intramuscular injection of QVLP (30 μg HA/strain) from three sequential lots. Local and systemic reactions were monitored for 21 days post-vaccination and blood was collected pre-vaccination and at day 21 (D21) after vaccination to measure hemagglutination inhibition (HI) antibodies.

RESULTS

Subject demographics were similar between groups and compliance with study procedures was 96.3%. The study population was 54.8% female, the mean age (±SD) was 29.9 ± 9.01 and the racial distribution was 77.8% Caucasian, 15.6% Asian, 5.8% Black/African American and 0.8% other. The HI responses met the Center for Biologics Evaluation and Research criteria for seroconversion (SCR ≥ 40%) and seroprotection rates (SPR ≥ 70%). The geometric mean fold rise in HI titers was ≥ 2.5 for all 4 strains for each lot. Lot-to-lot consistency was met with the 95% confidence intervals of the D21 mean geometric titre ratios falling between 0.67 and 1.5 for all four strains. No safety concerns were identified. Solicited adverse events were generally mild and transient: typical for what is reported after inactivated influenza vaccines.

CONCLUSIONS

This study supported earlier findings of the safety profile and immunogenicity of the plant-derived QVLP and demonstrated the consistency with which it can be produced.

Retrospective Assessment of the Antigenic Similarity of Egg-Propagated and Cell Culture-Propagated Reference Influenza Viruses as Compared with Circulating Viruses across Influenza Seasons 2002-2003 to 2017-2018

Suboptimal vaccine effectiveness against seasonal influenza is a significant public health concern, partly explained by antigenic differences between vaccine viruses and viruses circulating in the environment. Haemagglutinin mutations within vaccine viruses acquired during serial passage in eggs have been identified as a source of antigenic variation between vaccine and circulating viruses. This study retrospectively compared the antigenic similarity of circulating influenza isolates with egg- and cell-propagated reference viruses to assess any observable trends over a 16-year period. Using annual and interim reports published by the Worldwide Influenza Centre, London, for the 2002-2003 to 2017-2018 influenza seasons, we assessed the proportions of circulating viruses which showed antigenic similarity to reference viruses by season. Egg-propagated reference viruses were well matched against circulating viruses for A/H1N1 and B/Yamagata. However, A/H3N2 and B/Victoria cell-propagated reference viruses appeared to be more antigenically similar to circulating A/H3N2 and B/Victoria viruses than egg-propagated reference viruses. These data support the possibility that A/H3N2 and B/Victoria viruses are relatively more prone to egg-adaptive mutation. Cell-propagated A/H3N2 and B/Victoria reference viruses were more antigenically similar to circulating A/H3N2 and B/Victoria viruses over a 16-year period than were egg-propagated reference viruses.

Influenza Classification Suite: An automated Galaxy workflow for rapid influenza sequence analysis

Influenza viruses continually evolve to evade population immunity, and the different lineages are assigned into clades based on shared mutations. We have developed a publicly available computational workflow, the Influenza Classification Suite, for rapid clade mapping of sequenced influenza viruses. This suite provides a user‐friendly workflow implemented in Galaxy to automate clade calling and antigenic site extraction. Workflow input includes clade definition and amino acid index array files, which can be customized to identify any clades of interest. The Influenza Classification Suite provides rapid, high‐resolution understanding of circulating influenza strain evolution to inform influenza vaccine effectiveness and the need for potential vaccine reformulation.

Effectiveness of influenza vaccine against influenza A in Europe in seasons of different A(H1N1)pdm09 and the same A(H3N2) vaccine components (2016-17 and 2017-18)

•

Influenza A(H3N2) circulated in Europe in 2016–17 and 2017–18 and A(H1N1)pdm09 in 2017–18.

•

Changed A(H1N1)pdm09 vaccine component VE was 58% against A(H1N1)pdm09 in 2017–18.

•

A(H3N2) VE was 13% and 28% among all ages in 2016–17 and 2017–18, respectively.

Introduction

Influenza A(H3N2) viruses predominated in Europe in 2016–17. In 2017–18 A(H3N2) and A(H1N1)pdm09 viruses co-circulated. The A(H3N2) vaccine component was the same in both seasons; while the A(H1N1)pdm09 component changed in 2017–18. In both seasons, vaccine seed A(H3N2) viruses developed adaptations/alterations during propagation in eggs, impacting antigenicity.

Methods

We used the test-negative design in a multicentre primary care case-control study in 12 European countries to measure 2016–17 and 2017–18 influenza vaccine effectiveness (VE) against laboratory-confirmed influenza A(H1N1)pdm09 and A(H3N2) overall and by age group.

Results

During the 2017–18 season, the overall VE against influenza A(H1N1)pdm09 was 59% (95% CI: 47–69). Among those aged 0–14, 15–64 and ≥65 years, VE against A(H1N1)pdm09 was 64% (95% CI: 37–79), 50% (95% CI: 28–66) and 66% (95% CI: 42–80), respectively. Overall VE against influenza A(H3N2) was 28% (95% CI: 17–38) in 2016–17 and 13% (95% CI: −15 to 34) in 2017–18. Among 0–14-year-olds VE against A(H3N2) was 28% (95%CI: −10 to 53) and 29% (95% CI: −87 to 73), among 15–64-year-olds 34% (95% CI: 18–46) and 33% (95% CI: −3 to 56) and among those aged ≥65 years 15% (95% CI: −10 to 34) and −9% (95% CI: −74 to 32) in 2016–17 and 2017–18, respectively.

Conclusions

Our study suggests the new A(H1N1)pdm09 vaccine component conferred good protection against circulating strains, while VE against A(H3N2) was <35% in 2016–17 and 2017–18. The egg propagation derived antigenic mismatch of the vaccine seed virus with circulating strains may have contributed to this low effectiveness. A(H3N2) seed viruses for vaccines in subsequent seasons may be subject to the same adaptations; in years with lower than expected VE, recommendations of preventive measures other than vaccination should be given in a timely manner.

Determining optimal community protection strategies for the influenza vaccine

Introduction: Seasonal influenza poses a major risk to the health of the population. Optimal strategies for influenza vaccination can help to reduce this risk. Areas covered: Systematic evaluations of the burden of influenza are first reviewed. Key meta-analysis, randomized trials, and observational studies are critically reviewed to provide the best estimates of the efficacy of influenza vaccine. The concept of herd effect is first introduced and this is followed by the rationale and the evidence to support herd effect that can be provided with strategic use of influenza vaccination in populations. Challenges including the effect of repeated influenza vaccination and vaccine hesitancy are reviewed. The citations were selected by the authors based on PubMed searches of the literature. Expert opinion: Efforts to develop new vaccines, including a universal vaccine, offer the best prospects for improved herd effect. Increasing uptake in new populations can increase likelihood of a herd effect.