Enhanced immunogenicity of seasonal influenza vaccines in young children using MF59 adjuvant

A quadrivalent recombinant influenza Hemagglutinin vaccine induced strong protective immune responses in animal models

Globally, influenza poses a substantial threat to public health, serving as a major contributor to both morbidity and mortality. The current vaccines for seasonal influenza are not optimal. A novel recombinant hemagglutinin (rHA) protein-based quadrivalent seasonal influenza vaccine, SCVC101, has been developed. SCVC101-S contains standard dose protein (15μg of rHA per virus strain) and an oil-in-water adjuvant, CD-A, which enhances the immunogenicity and cross-protection of the vaccine. Preclinical studies in mice, rats, and rhesus macaques demonstrate that SCVC101-S induces robust humoral and cellular immune responses, surpassing those induced by commercially available vaccines. Notably, a single injection with SCVC101-S can induce a strong immune response in macaques, suggesting the potential for a standard-dose vaccination with a recombinant protein influenza vaccine. Furthermore, SCVC101-S induces cross-protection immune responses against heterologous viral strains, indicating broader protection than current vaccines. In conclusion, SCVC101-S has demonstrated safety and efficacy in preclinical settings and warrants further investigation in human clinical trials. Its potential as a valuable addition to the vaccines against seasonal influenza, particularly for the elderly population, is promising.

Adjuvants in cutaneous vaccination: A comprehensive analysis

Skin is the body's largest organ and serves as a protective barrier from physical, thermal, and mechanical environmental challenges. Alongside, the skin hosts key immune system players, such as the professional antigen-presenting cells (APCs) like the Langerhans cells in the epidermis and circulating macrophages in the blood. Further, the literature supports that the APCs can be activated by antigen or vaccine delivery via multiple routes of administration through the skin. Once activated, the stimulated APCs drain to the associated lymph nodes and gain access to the lymphatic system. This further allows the APCs to engage with the adaptive immune system and activate cellular and humoral immune responses. Thus, vaccine delivery via skin offers advantages such as reliable antigen delivery, superior immunogenicity, and convenient delivery. Several preclinical and clinical studies have demonstrated the significance of vaccine delivery using various routes of administration via skin. However, such vaccines often employ adjuvant/(s), along with the antigen of interest. Adjuvants augment the immune response to a vaccine antigen and improve the therapeutic efficacy. Due to these reasons, adjuvants have been successfully used with infectious disease vaccines, cancer immunotherapy, and immune-mediated diseases. To capture these developments, this review will summarize preclinical and clinical study results of vaccine delivery via skin in the presence of adjuvants. A focused discussion regarding the FDA-approved adjuvants will address the experiences of using such adjuvant-containing vaccines. In addition, the challenges and regulatory concerns with these adjuvants will be discussed. Finally, the review will share the prospects of adjuvant-containing vaccines delivered via skin.

Memory-like innate response to booster vaccination with MF-59 adjuvanted influenza vaccine in children

The pediatric population receives the majority of vaccines globally, yet there is a paucity of studies on the transcriptional response induced by immunization in this special population. In this study, we performed a systems-level analysis of immune responses to the trivalent inactivated influenza vaccine adjuvanted with MF-59 in children (15-24 months old) and in young, healthy adults. We analyzed transcriptional responses elicited by vaccination in peripheral blood, as well as cellular and antibody responses following primary and booster vaccinations. Our analysis revealed that primary vaccination induced a persistent transcriptional signature of innate immunity; booster vaccination induced a transcriptional signature of an enhanced memory-like innate response, which was consistent with enhanced activation of myeloid cells assessed by flow cytometry. Furthermore, we identified a transcriptional signature of type 1 interferon response post-booster vaccination and at baseline that was correlated with the local reactogenicity to vaccination and defined an early signature that correlated with the hemagglutinin antibody titers. These results highlight an adaptive behavior of the innate immune system in evoking a memory-like response to secondary vaccination and define molecular correlates of reactogenicity and immunogenicity in infants.

Formulation of Recombinant H1N1 Hemagglutinin in MF59 and Alum Adjuvants: A Comparison of the Vaccines Potency and Efficacy in BALB/C Mice

In this study, we reported the expression and potency of the recombinant H1N1 hemagglutinin (HA) vaccine as our in-house vaccine in a BALB/c mouse model. Recombinant H1N1 HA was produced in SF9 cell line, purified and formulated in MF59 adjuvant. Experimental mice were injected on days 0 and 14 with MF59-formulated vaccine, alum-based vaccine, and phosphate-buffered saline (PBS). Interleukin (IL)-2, IL-4, and interferon (IFN)-γ were assessed with commercial enzyme-linked immunosorbent assay (ELISA). Antibody responses and cytotoxic T lymphocyte (CTL) activity were assessed by hemagglutination inhibition and granzyme B ELISA, respectively. Moreover, the mice were challenged to show the vaccine efficacy. A considerable rise in IFN-γ and IL-4, as well as IFN-γ/IL-4 ratio, was observed in comparison with the alum-based vaccine and PBS group. Furthermore, our candidate vaccine showed superiority in humoral immune responses and CTL activity versus the alum-based vaccine and PBS group. The challenge showed that the survival rate in the vaccinated groups revealed a significant increase as compared with that in the PBS group. In conclusion, our candidate vaccine showed a robust Th1 response and CTL activity the alum-based vaccine. Moreover, a significant humoral immune response and a higher survival rate were detected in our vaccine as compared with the alum-based vaccine. It seems that the superiority of the MF59-based vaccine is due to the type of vaccine formulation in the candidate vaccine.

Adjuvants for COVID-19 Vaccines

In recent decades, the improvement of traditional vaccines has meant that we have moved from inactivated whole virus vaccines, which provoke a moderate immune response but notable adverse effects, to much more processed vaccines such as protein subunit vaccines, which despite being less immunogenic have better tolerability profiles. This reduction in immunogenicity is detrimental to the prevention of people at risk. For this reason, adjuvants are a good solution to improve the immunogenicity of this type of vaccine, with much better tolerability profiles and a low prevalence of side effects. During the COVID-19 pandemic, vaccination focused on mRNA-type and viral vector vaccines. However, during the years 2022 and 2023, the first protein-based vaccines began to be approved. Adjuvanted vaccines are capable of inducing potent responses, not only humoral but also cellular, in populations whose immune systems are weak or do not respond properly, such as the elderly. Therefore, this type of vaccine should complete the portfolio of existing vaccines, and could help to complete vaccination against COVID-19 worldwide now and over the coming years. In this review we analyze the advantages and disadvantages of adjuvants, as well as their use in current and future vaccines against COVID-19.

New-age vaccine adjuvants, their development, and future perspective

In the present scenario, immunization is of utmost importance as it keeps us safe and protects us from infectious agents. Despite the great success in the field of vaccinology, there is a need to not only develop safe and ideal vaccines to fight deadly infections but also improve the quality of existing vaccines in terms of partial or inconsistent protection. Generally, subunit vaccines are known to be safe in nature, but they are mostly found to be incapable of generating the optimum immune response. Hence, there is a great possibility of improving the potential of a vaccine in formulation with novel adjuvants, which can effectively impart superior immunity. The vaccine(s) in formulation with novel adjuvants may also be helpful in fighting pathogens of high antigenic diversity. However, due to the limitations of safety and toxicity, very few human-compatible adjuvants have been approved. In this review, we mainly focus on the need for new and improved vaccines; the definition of and the need for adjuvants; the characteristics and mechanisms of human-compatible adjuvants; the current status of vaccine adjuvants, mucosal vaccine adjuvants, and adjuvants in clinical development; and future directions.

Immunogenicity and safety of seasonal influenza vaccines in children under 3 years of age

INTRODUCTION

Despite children aged 6-35 months developing more severe influenza infections, not all countries include influenza vaccines in their national immunization programs.

AREAS COVERED

This literature review examines the efficacy, immunogenicity, and safety of seasonal trivalent influenza vaccines (TIVs) and quadrivalent influenzae vaccines (QIVs) in children 6-35 months old to determine if greater valency promotes greater protection while maintaining a similar safety profile.

EXPERT OPINION

TIVs and QIVs are safe for children under 3 years old. TIVs and QIVs provided good seroprotection, and immunogenicity (GMT, SCR, and SPR) meeting recommended levels set by CHMP (European) and CBER (USA). However, as QIVs carry two influenza B strains and TIVs only one, QIVs has an overall higher seroprotection against particularly influenza B. Vaccines containing adjuncts had better immunogenicity, particularly after the first dose. Seroprotection of all vaccines lasted 12 months. Increasing the dosage from 0.25 mL to 0.5 mL did not cause more systemic or local side-effects. Further comparisons of efficacy, and wider promotion of influenza vaccines in general are required in preschool children.

An Overview of Vaccine Adjuvants: Current Evidence and Future Perspectives

Vaccinations are one of the most important preventive tools against infectious diseases. Over time, many different types of vaccines have been developed concerning the antigen component. Adjuvants are essential elements that increase the efficacy of vaccination practises through many different actions, especially acting as carriers, depots, and stimulators of immune responses. For many years, few adjuvants have been included in vaccines, with aluminium salts being the most commonly used adjuvant. However, recent research has focused its attention on many different new compounds with effective adjuvant properties and improved safety. Modern technologies such as nanotechnologies and molecular biology have forcefully entered the production processes of both antigen and adjuvant components, thereby improving vaccine efficacy. Microparticles, emulsions, and immune stimulators are currently in the spotlight for their huge potential in vaccine production. Although studies have reported some potential side effects of vaccine adjuvants such as the recently recognised ASIA syndrome, the huge worth of vaccines remains unquestionable. Indeed, the recent COVID-19 pandemic has highlighted the importance of vaccines, especially in regard to managing future potential pandemics. In this field, research into adjuvants could play a leading role in the production of increasingly effective vaccines.

Developments in Vaccine Adjuvants

Vaccines, including subunit, recombinant, and conjugate vaccines, require the use of an immunostimulator/adjuvant for maximum efficacy. Adjuvants not only enhance the strength and longevity of immune responses but may also influence the type of response. In this chapter, we review the adjuvants that are available for use in human vaccines, such as alum, MF59, AS03, and AS01. We extensively discuss their composition, characteristics, mechanism of action, and effects on the immune system. Additionally, we summarize recent trends in adjuvant discovery, providing a brief overview of saponins, TLRs agonists, polysaccharides, nanoparticles, cytokines, and mucosal adjuvants.

"World in motion" - emulsion adjuvants rising to meet the pandemic challenges

Emulsion adjuvants such as MF59 and AS03 have been used for more than two decades as key components of licensed vaccines, with over 100 million doses administered to diverse populations in more than 30 countries. Substantial clinical experience of effectiveness and a well-established safety profile, along with the ease of manufacturing have established emulsion adjuvants as one of the leading platforms for the development of pandemic vaccines. Emulsion adjuvants allow for antigen dose sparing, more rapid immune responses, and enhanced quality and quantity of adaptive immune responses. The mechanisms of enhancement of immune responses are well defined and typically characterized by the creation of an "immunocompetent environment" at the site of injection, followed by the induction of strong and long-lasting germinal center responses in the draining lymph nodes. As a result, emulsion adjuvants induce distinct immunological responses, with a mixed Th1/Th2 T cell response, long-lived plasma cells, an expanded repertoire of memory B cells, and high titers of cross-neutralizing polyfunctional antibodies against viral variants. Because of these various properties, emulsion adjuvants were included in pandemic influenza vaccines deployed during the 2009 H1N1 influenza pandemic, are still included in seasonal influenza vaccines, and are currently at the forefront of the development of vaccines against emerging SARS-CoV-2 pandemic variants. Here, we comprehensively review emulsion adjuvants, discuss their mechanism of action, and highlight their profile as a benchmark for the development of additional vaccine adjuvants and as a valuable tool to allow further investigations of the general principles of human immunity.

Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%-96%) and young children (range = 50%-100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%-70% in pregnant women and 20%-90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

Influenza Vaccination for the Prevention of Cardiovascular Disease in the Americas: Consensus document of the Inter-American Society of Cardiology and the Word Heart Federation

Background

Cardiovascular mortality is decreasing but remains the leading cause of death world-wide. Respiratory infections such as influenza significantly contribute to morbidity and mortality in patients with cardiovascular disease. Despite of proven benefits, influenza vaccination is not fully implemented, especially in Latin America.

Objective

The aim was to develop a regional consensus with recommendations regarding influenza vaccination and cardiovascular disease.

Methods

A multidisciplinary team composed by experts in the management and prevention of cardiovascular disease from the Americas, convened by the Inter-American Society of Cardiology (IASC) and the World Heart Federation (WHF), participated in the process and the formulation of statements. The modified RAND/UCLA methodology was used. This document was supported by a grant from the WHF.

Results

An extensive literature search was divided into seven questions, and a total of 23 conclusions and 29 recommendations were achieved. There was no disagreement among experts in the conclusions or recommendations.

Conclusions

There is a strong correlation between influenza and cardiovascular events. Influenza vaccination is not only safe and a proven strategy to reduce cardiovascular events, but it is also cost saving. We found several barriers for its global implementation and potential strategies to overcome them.

Antibody Response and Protection After Receipt of Inactivated Influenza Vaccine: A Systematic Review

CONTEXT

Children are at increased risk of influenza-related complications. Public health agencies recommend 2 doses of influenza vaccine for children 6 months through 8 years of age receiving the vaccine for the first time.

OBJECTIVE

To systematically review studies comparing vaccine effectiveness (VE) and immunogenicity after 1 or 2 doses of inactivated influenza vaccine (IIV) in children.

DATA SOURCES

Data sources included Medline, Embase, and Cochrane Library databases.

STUDY SELECTION

We included studies published in a peer reviewed journal up to April 2, 2019, with available abstracts, written in English, and with children aged 6 months through 8 years.

DATA EXTRACTION

VE among fully and partially vaccinated children was compared with that of unvaccinated children. We extracted geometric mean titers of serum hemagglutination inhibition (HAI) antibodies against influenza A(H1N1), A(H3N2), and B-lineage vaccine antigens after 1 and 2 IIV doses. Outcomes were evaluated by age, timing of doses, vaccine composition, and prevaccination titers.

RESULTS

A total of 10 VE and 16 immunogenicity studies were included. VE was higher for fully vaccinated groups than partially vaccinated groups, especially for children aged 6-23 months. Our findings show increased HAI titers after 2 doses, compared with 1. Older children and groups with prevaccination antibodies have robust HAI titers after 1 dose. Similar vaccine strains across doses, not the timing of doses, positively affects immune response.

LIMITATIONS

Few studies focused on older children. Researchers typically administered one-half the standard dose of IIV. HAI antibodies are an imperfect correlate of protection.

CONCLUSIONS

Findings support policies recommending 2 IIV doses in children to provide optimal protection against influenza.

Influenza Chimeric Protein (3M2e-3HA2-NP) Adjuvanted with PGA/Alum Confers Cross-Protection against Heterologous Influenza A Viruses

Vaccination is the most effective way to prevent influenza virus infections. However, conventional vaccines based on hemagglutinin (HA) have to be annually updated because the HA of influenza viruses constantly mutates. In this study, we produced a 3M2e-3HA2-NP chimeric protein as a vaccine antigen candidate using an Escherichia coli expression system. The vaccination of chimeric protein (15 μg) conferred complete protection against A/Puerto Rico/8/1934 (H1N1; PR8) in mice. It strongly induced influenza virus-specific antibody responses, cytotoxic T lymphocyte activity, and antibody-dependent cellular cytotoxicity. To spare the dose and enhance the cross-reactivity of the chimeric, we used a complex of poly-γ-glutamic acid and alum (PGA/alum) as an adjuvant. PGA/alum-adjuvanted, low-dose chimeric protein (1 or 5 μg) exhibited higher cross-protective effects against influenza A viruses (PR8, CA04, and H3N2) compared with those of chimeric alone or alum-adjuvanted proteins in vaccinated mice. Moreover, the depletion of CD4+ T, CD8+ T, and NK cells reduced the survival rate and efficacy of the PGA/alum-adjuvanted chimeric protein. Collectively, the vaccination of PGA/alum-adjuvanted chimeric protein induced strong protection efficacy against homologous and heterologous influenza viruses in mice, which suggests that it may be a promising universal influenza vaccine candidate.

Immune Responses to Adjuvanted H7N9 Split Antigen in Aged Mice

The avian influenza A H7N9 virus has caused severe infection and high mortality in humans. It can be extremely hazardous to the elderly since age might diminish the immune response, and poor immunogenicity of H7 hemagglutinin could diminish the vaccine efficacy in this population. To overcome this issue, adjuvants are used to induce a stronger immune response. In this study, we generated a recombinant H7N9 influenza virus using reverse genetic techniques, consisting of hemagglutinin and neuraminidase genes derived from a human H7N9 virus, with the remaining genes from H1N1 A/Puerto Rico/8/34 (PR8). To evaluate whether the adjuvant can improve immune responses in aged animals, the humoral and cellular immune responses of 18-month-old BALB/c mice to different doses of split avian influenza A H7N9 vaccine with and without the adjuvant MF59 were compared. Our data showed that aged mice immunized with MF59 elicited higher levels of hemagglutination inhibition and microneutralization antibodies and interferon-gamma-specific enzyme-linked immunospot assay (ELISPOT) responses when compared with antigens alone. It is suggested that the split avian influenza A H7N9 vaccine combined with MF59 may significantly improve immune responses to influenza vaccination in elderly humans.

Engineered Nanoparticle Applications for Recombinant Influenza Vaccines

Influenza viruses cause seasonal epidemics and represent a pandemic risk. With current vaccine methods struggling to protect populations against emerging strains, there is a demand for a next-generation flu vaccine capable of providing broad protection. Recombinant biotechnology, combined with nanomedicine techniques, could address this demand by increasing immunogenicity and directing immune responses toward conserved antigenic targets on the virus. Various nanoparticle candidates have been tested for use in vaccines, including virus-like particles, protein and carbohydrate nanoconstructs, antigen-carrying lipid particles, and synthetic and inorganic particles modified for antigen presentation. These methods have yielded some promising results, including protection in animal models against antigenically distinct influenza strains, production of antibodies with broad reactivity, and activation of potent T cell responses. Based on the evidence of current research, it is feasible that the next generation of influenza vaccines will combine recombinant antigens with nanoparticle carriers.

Antibody Responses to SARS-CoV-2: Let's Stick to Known Knowns

The scale of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has thrust immunology into the public spotlight in unprecedented ways. In this article, which is part opinion piece and part review, we argue that the normal cadence by which we discuss science with our colleagues failed to properly convey likelihoods of the immune response to SARS-CoV-2 to the public and the media. As a result, biologically implausible outcomes were given equal weight as the principles set by decades of viral immunology. Unsurprisingly, questionable results and alarmist news media articles have filled the void. We suggest an emphasis on setting expectations based on prior findings while avoiding the overused approach of assuming nothing. After reviewing Ab-mediated immunity after coronavirus and other acute viral infections, we posit that, with few exceptions, the development of protective humoral immunity of more than a year is the norm. Immunity to SARS-CoV-2 is likely to follow the same pattern.

Self-Assembled Nanoparticles: Exciting Platforms for Vaccination

Vaccination is successfully advanced to control several fatal diseases and improve human life expectancy. However, additional innovations are required in this field because there are no effective vaccines to prevent some infectious diseases. The shift from the attenuated or inactivated pathogens to safer but less immunogenic protein or peptide antigens has led to a search for effective antigen delivery carriers that can function as both antigen vehicles and intrinsic adjuvants. Among these carriers, self-assembled nanoparticles (SANPs) have shown great potential to be the best representative. For the nanoscale and multiple presentation of antigens, with accurate control over size, geometry, and functionality, these nanoparticles are assembled spontaneously and mimic pathogens, resulting in enhanced antigen presentation and increased cellular and humoral immunity responses. In addition, they may be applied through needle-free routes due to their adhesive ability, which gives them a great future in vaccination applications. This review provides an overview of various SANPs and their applications in prophylactic vaccines.

Oil-in-water emulsion adjuvants for pediatric influenza vaccines: a systematic review and meta-analysis

Standard inactivated influenza vaccines are poorly immunogenic in immunologically naive healthy young children, who are particularly vulnerable to complications from influenza. For them, there is an unmet need for better influenza vaccines. Oil-in-water emulsion-adjuvanted influenza vaccines are promising candidates, but clinical trials yielded inconsistent results. Here, we meta-analyze randomized controlled trials with efficacy data (3 trials, n = 15,310) and immunogenicity data (17 trials, n = 9062). Compared with non-adjuvanted counterparts, adjuvanted influenza vaccines provide a significantly better protection (weighted estimate for risk ratio of RT-PCR-confirmed influenza: 0.26) and are significantly more immunogenic (weighted estimates for seroprotection rate ratio: 4.6 to 7.9) in healthy immunologically naive young children. Nevertheless, in immunologically non-naive children, adjuvanted and non-adjuvanted vaccines provide similar protection and are similarly immunogenic. These results indicate that oil-in-water emulsion adjuvant improves the efficacy of inactivated influenza vaccines in healthy young children at the first-time seasonal influenza vaccination.

Priming with MF59 adjuvanted versus nonadjuvanted seasonal influenza vaccines in children - A systematic review and a meta-analysis

BACKGROUND

Identifying optimal priming strategies for children <2 years could substantially improve the public health benefits of influenza vaccines. Adjuvanted seasonal influenza vaccines were designed to promote a better immune response among young vaccine-naïve children.

METHODS

We systematically reviewed randomized trials to assess hemagglutination inhibition (HAI) antibody response to MF59-adjuvanted inactivated influenza vaccine (aIIV) versus nonadjuvanted IIV among children. We estimated pooled ratios of post-vaccination HAI geometric mean titer (GMT) for aIIV versus IIV and confidence intervals (CIs) using the pooled variances derived from reported CIs.

RESULTS

Mean age was 28 months (range, 6-72 months). Children received vaccines with either 7.5 μg (6-35 months) or 15 μg (≥36 months) hemagglutinin of each strain depending on age. Seven of eight trials administered trivalent vaccines and one used quadrivalent vaccine. Pooled post-vaccination GMT ratios against the three influenza vaccine strains were 2.5-3.5 fold higher after 2-dose-aIIV versus 2-dose-IIV among children 6-72 months, and point estimates were higher among children 6-35 months compared with older children. When comparing 1-dose-aIIV to 2-dose-IIV doses, pooled GMT ratios were not significantly different against A/H1N1 (1.0; 95% CI: 0.5-1.8; p = 0.90) and A/H3N2 viruses (1.0; 95% CI: 0.7-1.5; p = 0.81) and were significantly lower against B viruses (0.6; 95% CI: 0.4-0.8; p < 0.001) for both age groups. Notably, GMT ratios for vaccine-mismatched heterologous viruses after 2-dose-aIIV compared with 2-dose-IIV were higher against A/H1N1 (2.0; 95% CI: 1.1-3.4), A/H3N2 (2.9; 95% CI: 1.9-4.2), and B-lineage viruses (2.1; 95% CI: 1.8-2.6).

CONCLUSIONS

Two doses of adjuvanted IIV consistently induced better humoral immune responses against Type A and B influenza viruses compared with nonadjuvanted IIVs in young children, particularly among those 6-35 months. One adjuvanted IIV dose had a similar response to two nonadjuvanted IIV doses against Type A influenza viruses. Longer-term benefits from imprinting and cell-mediated immunity, including trials of clinical efficacy, are gaps that warrant investigation.

Vaccine-associated hypersensitivity

Vaccine-associated hypersensitivity reactions are not infrequent; however, serious acute-onset, presumably IgE-mediated or IgG and complement-mediated anaphylactic or serious delayed-onset T cell-mediated systemic reactions are considered extremely rare. Hypersensitivity can occur because of either the active vaccine component (antigen) or one of the other components. Postvaccination acute-onset hypersensitivity reactions include self-limited localized adverse events and, rarely, systemic reactions ranging from urticaria/angioedema to full-blown anaphylaxis with multisystem involvement. Risk of anaphylaxis after all vaccines is estimated to be 1.31 (95% CI, 0.90-1.84) per million vaccine doses, respectively. Serious hypersensitivity reactions after influenza vaccines are particularly important because of the large number of persons vaccinated annually. Influenza vaccines are unique in requiring annual changes in the vaccines' antigenic composition to match the predicted circulating influenza strains. Recently, novel influenza vaccine types were introduced in the United States (recombinant vaccines, some with higher antigen content and a new adjuvanted vaccine). Providers should be aware of changing recommendations on the basis of recent published evidence for persons with a history of egg allergy to receive annual influenza vaccination. Further research is needed to elucidate the pathophysiology and risk factors for reported vaccine-associated adverse events. Further research is also needed to determine whether repeated annual inactivated influenza vaccination, the number of vaccine antigens administered at the same time, and the current timing of routine infant vaccinations are optimal for overall population well-being.

MF59-adjuvanted seasonal trivalent inactivated influenza vaccine: Safety and immunogenicity in young children at risk of influenza complications

OBJECTIVE

To assess the safety and immunogenicity of the MF59-adjuvanted seasonal trivalent inactivated influenza vaccine (aIIV3; Fluad) in children aged 6 months through 5 years who are at risk of influenza complications.

METHODS

A retrospective analysis was performed to examine unsolicited adverse events (AEs) in an integrated dataset from six randomized clinical studies that compared aIIV3 with non-adjuvanted inactivated influenza vaccines (IIV3). The integrated safety set comprised 10 784 children, of whom 373 (3%) were at risk of influenza complications.

RESULTS

The at-risk safety population comprised 373 children aged 6 months through 5 years: 179 received aIIV3 and 194 received non-adjuvanted IIV3 (128 subjects received a licensed IIV3). The most important risk factors were respiratory system illnesses (62-70%) and infectious and parasitic diseases (33-39%). During the treatment period, unsolicited AEs occurred in 54% of at-risk children and 55% of healthy children who received aIIV3; of those receiving licensed IIV3, 59% of at-risk and 62% of healthy subjects reported an unsolicited AE. The most common AEs were infections, including upper respiratory tract infection. Serious AEs (SAEs) were reported in <10% of at-risk subjects, and no vaccine-related SAEs were observed. In the immunogenicity subset (involving 103 participants from one study), geometric mean titers (GMTs) were approximately 2- to 3-fold higher with aIIV3 than with IIV3 for all three homologous strains (A/H1N1, A/H3N2, and B). Seroconversion rates were high for both aIIV3 (79-96%) and IIV3 (83-89%).

CONCLUSIONS

In young children at risk of influenza complications, aIIV3 was well-tolerated and had a safety profile that was generally similar to that of non-adjuvanted IIV3. Similar to the not-at-risk population, the immune response in at-risk subjects receiving aIIV3 was increased over those receiving IIV3, suggesting aIIV3 is a valuable option in young children at risk of influenza complications.

Inactivated whole virus particle vaccine with potent immunogenicity and limited IL-6 induction is ideal for influenza

In contrast to current ether- or detergent-disrupted "split" vaccines (SVs) for influenza, inactivated whole influenza virus particle vaccines (WPVs) retain the original virus structure and components and as such may confer similar immunity to natural infection. In a collaboration between academia and industry, the potential of WPV as a new seasonal influenza vaccine was investigated. Each of the four seasonal influenza vaccine manufacturers in Japan prepared WPVs and SVs from the same batches of purified influenza virus. Both mice and monkeys vaccinated with the WPVs exhibited superior immune responses to those vaccinated with the corresponding SVs. Vaccination with A/California/07/2009 (H1N1) WPV enabled mice to survive a lethal challenge dose of homologous virus whereas those vaccinated with SV succumbed to infection within 6 days. Furthermore, mice vaccinated with WPV induced substantial numbers of multifunctional CD8⁺ T cells, important for control of antigenically drifted influenza virus strains. In addition, cytokines and chemokines were detected at early time points in the sera of mice vaccinated with WPV but not in those animals vaccinated with SV. These results indicate that WPVs induce enhanced innate and adaptive immune responses compared to equivalent doses of SVs. Notably, WPV at one fifth of the dose of SV was able to induce potent immunity with limited production of IL-6, one of the pyrogenic cytokines. We thus propose that WPVs with balanced immunogenicity and safety may set a new global standard for seasonal influenza vaccines.

Adjuvanted influenza vaccine dynamics

Adjuvanted influenza vaccines constitute a key element towards inducing neutralizing antibody responses in populations with reduced responsiveness, such as infants and elderly subjects, as well as in devising antigen-sparing strategies. In particular, squalene-containing adjuvants have been observed to induce enhanced antibody responses, as well as having an influence on cross-reactive immunity. To explore the effects of adjuvanted vaccine formulations on antibody response and their relation to protein-specific immunity, we propose different mathematical models of antibody production dynamics in response to influenza vaccination. Data from ferrets immunized with commercial H1N1pdm09 vaccine antigen alone or formulated with different adjuvants was instrumental to adjust model parameters. While the affinity maturation process complexity is abridged, the proposed model is able to recapitulate the essential features of the observed dynamics. Our numerical results suggest that there exists a qualitative shift in protein-specific antibody response, with enhanced production of antibodies targeting the NA protein in adjuvanted versus non-adjuvanted formulations, in conjunction with a protein-independent boost that is over one order of magnitude larger for squalene-containing adjuvants. Furthermore, simulations predict that vaccines formulated with squalene-containing adjuvants are able to induce sustained antibody titers in a robust way, with little impact of the time interval between immunizations.

Immunogenicity and safety of MF59-adjuvanted and full-dose unadjuvanted trivalent inactivated influenza vaccines among vaccine-naïve children in a randomized clinical trial in rural Senegal

INTRODUCTION

Effective, programmatically suitable influenza vaccines are needed for low-resource countries.

MATERIALS AND METHODS

This phase II, placebo-controlled, randomized safety and immunogenicity trial (NCT01819155) was conducted in Senegal using the 2012-2013 Northern Hemisphere trivalent influenza vaccine (TIV) formulation. Participants were allocated in a 2:2:1 ratio to receive TIV (full-dose for all age groups), adjuvanted TIV (aTIV), or placebo. Participants were stratified into age groups: 6-11, 12-35, and 36-71 months. All participants were vaccine-naïve and received two doses of study vaccine 4 weeks apart. The two independent primary objectives were to estimate the immunogenicity of TIV and of aTIV as the proportion of children with a hemagglutination inhibition (HI) antibody titer of ≥1:40 to each vaccine strain at 28 days post-dose two. Safety was evaluated by solicited local and systemic reactions, unsolicited adverse events, and serious adverse events.

RESULTS

296 children received TIV, aTIV, or placebo, and 235 were included in the final analysis. After two doses, children aged 6-11, 12-35, and 36-71 months receiving TIV had HI titers ≥1:40 against A/H1N1 (73.1%, 94.1%, and 97.0%), A/H3N2 (96.2%, 100.0%, and 100.0%), and B (80.8%, 97.1%, and 97.0%), respectively. After two doses, 100% children aged 6-11, 12-35, and 36-71 months receiving aTIV had ≥1:40 titers against A/H1N1, A/H3N2, and B. After a single dose, the aTIV response was comparable to or greater than the TIV response for all vaccine strains. TIV and aTIV reactogenicity were similar, except for mild elevation in temperature (37.5-38.4 °C) which occurred more frequently in aTIV than TIV after each vaccine dose. TIV and aTIV had similarly increased pain/tenderness at the injection site compared to placebo.

CONCLUSIONS

Both aTIV and full-dose TIV were well-tolerated and immunogenic in children aged 6-71 months. These vaccines may play a role in programmatically suitable strategies to prevent influenza in low-resource settings.

Prospective randomized open-label comparative study of immunogenicity after subunit and polymeric subunit influenza vaccines administration among mothers and infants

Pregnant women are risk group for influenza infection. Results of new subunit vaccines application have not been studied enough. Prospective, randomized, open-label comparative study of subunit (Agrippal) and polymeric subunit (Grippol plus) vaccines. 42 pairs of mothers-infants were participated in the study. Protective antibodies (≥ 1:40) to different influenza strains were registered on day 1 after the birth on the same level as 53% of cases in pairs mothers-infants after immune adjuvant polymeric subunit and subunit vaccines administration. There were the same level of protective antibodies (AB) among mothers after 3 month, but transplacental antibodies decreased among infants and registered in the 13-22% cases of Grippol plus group and 31-43% cases in Agrippal S1 group. AB titre to influenza virus A/H1N1/pdm09 and A/H3N2/in pairs mothers-infants were the same in both groups in first days after birth, but AB levels to B strain were lower among infants without regard to vaccine. There is no difference in AB titres among infants of both groups at 3 month of age, but their levels were twice lower versus initial data. An immune adjuvant polymeric subunit as well as subunit vaccines application in pregnant women forms protective AB in pairs mothers-infants.

Analysis of the dose-sparing effect of adjuvanted Sabin-inactivated poliovirus vaccine (sIPV)

Sabin-based inactivated poliovirus vaccine(sIPV) is gradually replacing live-attenuated oral polio vaccine(OPV). Sabin-inactivated poliovirus vaccine(sIPV) has played a vital role in reducing economic burden of poliomyelitis and maintaining appropriate antibody levels in the population. However, due to its high cost and limited manufacturing capacity, sIPV cannot reach its full potential for global poliovirus eradication in developing countries. Therefore, to address this situation, we designed this study to evaluate the dose-sparing effects of AS03, CpG oligodeoxynucleotides (CpG-ODN) and polyinosinic:polycytidylic acid (PolyI:C) admixed with sIPV in rats. Our results showed that a combination of 1/4-dose sIPV adjuvanted with AS03 or AS03 with BW006 provides a seroconversion rate similar to that of full-dose sIPV without adjuvant and that, this rate is 5-fold higher than that of 1/4-dose sIPV without adjuvant after the first immunization. The combination of AS03 or AS03 with BW006 as an adjuvant effectively reduced sIPV dose by at least 4-fold and induced both humoral and cellular immune responses. Therefore, our study revealed that the combination of AS03 or AS03 with BW006 is a promising adjuvant for sIPV development.

Seasonal influenza vaccine in immunocompromised persons

Immunocompromised persons are at high risk of complications from influenza infection. This population includes those with solid organ transplants, hematopoietic stem cell transplants, solid cancers and hematologic malignancy as well as those with autoimmune conditions receiving biologic therapies. In this review, we discuss the impact of influenza infection and evidence for vaccine effectiveness and immunogenicity. Overall, lower respiratory disease from influenza is common; however, vaccine immunogenicity is low. Despite this, in some populations, influenza vaccine has demonstrated effectiveness in reducing severe disease. Various strategies to improve influenza vaccine immunogenicity have been attempted including two vaccine doses in the same influenza season, intradermal, adjuvanted, and high-dose vaccines. The timing of influenza vaccine is also important to achieve optimal immunogenicity. Given the suboptimal immunogenicity, family members and healthcare professionals involved in the care of these populations should be vaccinated. Health care professional recommendation for vaccination is an important factor in vaccine coverage.

Opinion: Making Inactivated and Subunit-Based Vaccines Work

Empirically derived vaccines have in the past relied on the isolation and growth of disease-causing microorganisms that are then inactivated or attenuated before being administered. This is often done without prior knowledge of the mechanisms involved in conferring protective immunity. Recent advances in scientific technologies and in our knowledge of how protective immune responses are induced enable us to rationally design novel and safer vaccination strategies. Such advances have accelerated the development of inactivated whole-organism- and subunit-based vaccines. In this review, we discuss ideal attributes and criteria that need to be considered for the development of vaccines and some existing vaccine platforms. We focus on inactivated vaccines against influenza virus and ways by which vaccine efficacy can be improved with the use of adjuvants and Toll-like receptor-2 signaling.

AS03- and MF59-Adjuvanted Influenza Vaccines in Children

Influenza is a major cause of respiratory disease leading to hospitalization in young children. However, seasonal trivalent influenza vaccines (TIVs) have been shown to be ineffective and poorly immunogenic in this population. The development of live-attenuated influenza vaccines and adjuvanted vaccines are important advances in the prevention of influenza in young children. The oil-in-water emulsions MF59 and adjuvant systems 03 (AS03) have been used as adjuvants in both seasonal adjuvanted trivalent influenza vaccines (ATIVs) and pandemic monovalent influenza vaccines. Compared with non-adjuvanted vaccine responses, these vaccines induce a more robust and persistent antibody response for both homologous and heterologous influenza strains in infants and young children. Evidence of a significant improvement in vaccine efficacy with these adjuvanted vaccines resulted in the use of the monovalent (A/H1N1) AS03-adjuvanted vaccine in children in the 2009 influenza pandemic and the licensure of the seasonal MF59 ATIV for children aged 6 months to 2 years in Canada. The mechanism of action of MF59 and AS03 remains unclear. Adjuvants such as MF59 induce proinflammatory cytokines and chemokines, including CXCL10, but independently of type-1 interferon. This proinflammatory response is associated with improved recruitment, activation and maturation of antigen presenting cells at the injection site. In young children MF59 ATIV produced more homogenous and robust transcriptional responses, more similar to adult-like patterns, than did TIV. Early gene signatures characteristic of the innate immune response, which correlated with antibody titers were also identified. Differences were detected when comparing child and adult responses including opposite trends in gene set enrichment at day 3 postvaccination and, unlike adult data, a lack of correlation between magnitude of plasmablast response at day 7 and antibody titers at day 28 in children. These insights show the utility of novel approaches in understanding new adjuvants and their importance for developing improved influenza vaccines for children.

Report on eighth WHO meeting on development of influenza vaccines that induce broadly protective and long-lasting immune responses: Chicago, USA, 23-24 August 2016

In August 2016, the World Health Organization (WHO) convened the "Eighth meeting on development of influenza vaccines that induce broadly protective and long-lasting immune responses" to discuss the regulatory requirements and pathways for licensure of next-generation influenza vaccines, and to identify areas where WHO can promote the development of such vaccines. Participants included approximately 120 representatives of academia, the vaccine industry, research and development funders, and regulatory and public health agencies. They reviewed the draft WHO preferred product characteristics (PPCs) of vaccines that could address prioritized unmet public health needs and discussed the challenges facing the development of such vaccines, especially for low- and middle-income countries (LMIC). They defined the data desired by public-health decision makers globally and explored how to support the progression of promising candidates into late-stage clinical trials and for all countries. This report highlights the major discussions of the meeting.

Heterologous Immune Responses to Influenza Vaccine in Kidney Transplant Recipients

Influenza vaccine is known to have suboptimal immunogenicity in transplant recipients. Despite this, influenza vaccine may have the added benefit of inducing a cross-reactive immune response to viral strains not found in the vaccine. This is termed "heterologous immunity" and has not been assessed previously in transplant patients. Pre- and postvaccination sera from kidney transplant recipients (n = 60) immunized with the 2012-2013 adjuvanted or nonadjuvanted influenza vaccine underwent testing by hemagglutination inhibition assay for strains not present in vaccine: A/New Caledonia/20/99 (H1N1), A/Texas/50/2012 (H3N2) and B/Brisbane/60/2008. The geometric mean titer of antibody to heterologous strains increased after vaccine (H1N1: 80.0 to 136.1, p < 0.001; H3N2: 23.3 to 77.3, p < 0.001; B: 13.3 to 19.5, p < 0.001). Seroconversion rates were 16.7%, 41.7%, and 13.3%, respectively. No differences in heterologous response were seen in the adjuvanted versus nonadjuvanted groups. Patients were more likely to seroconvert for a cross-reactive antigen if they seroconverted for the specific vaccine antigen. Seroconversion to heterologous A/H3N2, for example, was 84.0% for homologous H3N2 seroconverters versus 11.4% for nonseroconverters (p < 0.001). This study provides novel evidence that transplant recipients are able to mount significant cross-protective responses to influenza vaccine that may be an additional, previously unknown benefit of immunization.

Seasonal Influenza Vaccination of Children Induces Humoral and Cell-Mediated Immunity Beyond the Current Season: Cross-reactivity With Past and Future Strains

BACKGROUND

Influenza viruses gradually accumulate point mutations, reducing the effectiveness of prior immune protection.

METHODS

Children aged 9-14 years received 2010-2011 trivalent inactivated influenza vaccine (TIV). Vaccination history, hemagglutination-inhibition (HI) titers, and cell-mediated immune responses were assessed to investigate the cross-reactivity with past and future influenza virus strains.

RESULTS

2010-2011 TIV induced significant T-cell responses and HI titers of ≥160, with a fold-rise of ≥4 and titers of ≥100 maintained for >7 months in the majority of children. Pre-existing memory B cells in these children differentiated quickly to antibody-secreting cells to the new vaccine antigens. Children vaccinated in the previous year maintained high HI titers well into 2010, demonstrating elevated HI titers against A/Perth/16/2009, the future (in 2010-2011) H3N2 component. Prior vaccination enhanced CD8+ T-cell responses to A/Perth/16/2009. Children vaccinated with the prior 2009-2010 seasonal vaccine also demonstrated higher preexisting levels of interferon γ-secreting CD4+CD69+ T cells to 2009 pandemic influenza A(H1N1). Children previously vaccinated with 2009-2010 seasonal influenza vaccine also showed greater expansion of tumor necrosis factor α-secreting CD8+CD69+ T cells to 2009 pandemic influenza A(H1N1) upon vaccination in the 2010-2011 season than those who were not previously vaccinated.

CONCLUSIONS

Seasonal influenza viruses continuously drift, which allows them to circumvent protective immunity, but conserved epitopes provide immunological cross-reactivity in children through either vaccination directly or through prime/boost in the prior influenza season.

A phase 1, open-label, randomized study to compare the immunogenicity and safety of different administration routes and doses of virosomal influenza vaccine in elderly

BACKGROUND

Influenza remains a significant problem in elderly despite widespread vaccination coverage. This randomized, phase-I study in elderly compared different strategies of improving vaccine immunogenicity.

METHODS

A total of 370 healthy participants (⩾65years) were randomized equally 1:1:1:1:1:1 to six influenza vaccine treatments (approximately 60-63 participants per treatment arm) at day 1 that consisted of three investigational virosomal vaccine formulations at doses of 7.5, 15, and 45μg HA antigen/strain administered intradermally (ID) by MicronJet600™ microneedle device (NanoPass Technologies) or intramuscularly (IM), and three comparator registered seasonal vaccines; Inflexal V™ (Janssen) and MF59 adjuvanted Fluad™ (Novartis) administered IM and Intanza™ (Sanofi Pasteur) administered ID via Soluvia™ prefilled microinjection system (BD). Serological evaluations were performed at days 22 and 90 and safety followed-up for 6months.

RESULTS

Intradermal delivery of virosomal vaccine using MicronJet600™ resulted in significantly higher immunogenicity than the equivalent dose of virosomal Inflexal V™ administered intramuscularly across most of the parameters and strains, as well as in some of the readouts and strains as compared with the 45μg dose of virosomal vaccine formulation. Of 370 participants, 300 (81.1%) reported ⩾1 adverse event (AE); more participants reported solicited local AEs (72.2%) than solicited systemic AEs (12.2%).

CONCLUSIONS

Intradermal delivery significantly improved influenza vaccine immunogenicity compared with intramuscular delivery. Triple dose (45μg) virosomal vaccine did not demonstrate any benefit on vaccine's immunogenicity over 15μg commercial presentation. All treatments were generally safe and well-tolerated.

Protection of young children from influenza through universal vaccination

Influenza is a very common disease among infants and young children, with a considerable clinical and socioeconomic impact. A significant number of health authorities presently recommend universal influenza vaccination for the pediatric population, but a large number of European health authorities is still reluctant to include influenza vaccination in their national vaccination programs. The reasons for this reluctance include the fact that the protection offered by the currently available vaccines is considered poor. This review shows that although future research could lead to an increase in the immunogenicity and potential efficacy of influenza vaccines, the available vaccines, even with their limits, assure sufficient protection in most subjects aged ≥ 6 months, thus reducing the total burden of influenza in young children and justifying the recommendation for the universal vaccination of the whole pediatric population. For younger subjects, the vaccination of their mother during pregnancy represents an efficacious strategy.

Development of a stable liquid formulation of live attenuated influenza vaccine

Vaccination is the most effective means of preventing influenza. However, the cost of producing annual seasonal influenza vaccines puts them out of reach for most developing countries. While live attenuated influenza vaccines are among the most efficacious and can be manufactured at low cost, they may require lyophilization to be stable enough for developing-country use, which adds a significant cost burden. The development of a liquid live attenuated seasonal influenza vaccine that is stable for around a year-the duration of an annual influenza season-would significantly improve not only the production output but also the use and accessibility of influenza vaccines in low-resource settings. In this study, potential stabilizing excipients were screened and optimized using the least stable influenza vaccine strain presently known, H1N1 (A/California/07/2009), as a model. The stability-conferring properties of the lead formulations were also tested with a Type B strain of influenza virus (B/Brisbane/60/2008). Stability was also evaluated with higher titers of influenza virus and exposure to agitation and freeze-thaw stresses to further confirm the stability of the lead formulations. Through this process, we identified a liquid formulation consisting of sucrose phosphate glutamate buffer with 1% arginine and 0.5% recombinant human serum albumin that provided storage stability of one year at 2-8°C for the influenza A and B strains tested.

Adjuvants: Classification, Modus Operandi, and Licensing

Vaccination is one of the most efficient strategies for the prevention of infectious diseases. Although safer, subunit vaccines are poorly immunogenic and for this reason the use of adjuvants is strongly recommended. Since their discovery in the beginning of the 20th century, adjuvants have been used to improve immune responses that ultimately lead to protection against disease. The choice of the adjuvant is of utmost importance as it can stimulate protective immunity. Their mechanisms of action have now been revealed. Our increasing understanding of the immune system, and of correlates of protection, is helping in the development of new vaccine formulations for global infections. Nevertheless, few adjuvants are licensed for human vaccines and several formulations are now being evaluated in clinical trials. In this review, we briefly describe the most well known adjuvants used in experimental and clinical settings based on their main mechanisms of action and also highlight the requirements for licensing new vaccine formulations.

A phase 1, open-label safety and immunogenicity study of an AS03-adjuvanted trivalent inactivated influenza vaccine in children aged 6 to 35 months

Background: There is a need for better vaccines and vaccine strategies to reduce the burden of influenza in very young children.

 

Methods: This phase 1, open-label study assessed the reactogenicity, safety, and immunogenicity of an inactivated trivalent influenza vaccine (TIV) containing low doses of hemagglutinin antigen (7.5 µg each strain), adjuvanted with a tocopherol-based oil-in-water emulsion Adjuvant System (AS03). Influenza vaccine-naïve children aged 6–35 months were sequentially enrolled to receive TIV-AS03_D (1.48 mg tocopherol) or TIV-AS03_C (2.97 mg tocopherol), then a 6-month booster of conventional TIV. The primary endpoint was the incidence of fever (axillary temperature >38 °C) for 7 days post-vaccination. Immune responses were assessed by hemagglutination-inhibition (HI) assay.

Results: Forty children were sequentially enrolled into the TIV-AS03_D or the TIV-AS03_C group. Fever >38.0 °C was reported in 5/20 (25.0%) and 7/20 (35.0%) children after the first and second doses of TIV-AS03_D, respectively, and in 7/20 (35.0%) children after 1 dose of TIV-AS03_C; the latter fulfilled the holding rule for safety, and the second dose of TIV-AS03_C was cancelled. HI immune responses exceeded adult European licensure criteria for the immunogenicity, and all children had HI antibody titers ≥ 1:40 after 1 dose of TIV booster against booster strains.

Conclusions: One dose of primary vaccine containing a low dose of antigen and AS03 may be a possible influenza vaccination strategy for young children. The relatively high frequency of fever warrants further investigation, although the generalizability of the findings are uncertain given that many of the children had antibody evidence suggesting recent infection with A(H1N1)pdm09.

A systematic review and meta-analysis on the safety of newly adjuvanted vaccines among children

INTRODUCTION

New adjuvants such as the AS- or the MF59-adjuvants improve vaccine efficacy and facilitate dose-sparing. Their use in influenza and malaria vaccines has resulted in a large body of evidence on their clinical safety in children.

METHODS

We carried out a systematic search for safety data from published clinical trials on newly adjuvanted vaccines in children ≤10 years of age. Serious adverse events (SAEs), solicited AEs, unsolicited AEs and AEs of special interest were evaluated for four new adjuvants: the immuno-stimulants containing adjuvant systems AS01 and AS02, and the squalene containing oil-in-water emulsions AS03 and MF59. Relative risks (RR) were calculated, comparing children receiving newly adjuvanted vaccines to children receiving other vaccines with a variety of antigens, both adjuvanted and unadjuvanted.

RESULTS

Twenty-nine trials were included in the meta-analysis, encompassing 25,056 children who received at least one dose of the newly adjuvanted vaccines. SAEs did not occur more frequently in adjuvanted groups (RR 0.85, 95%CI 0.75-0.96). Our meta-analyses showed higher reactogenicity following administration of newly adjuvanted vaccines, however, no consistent pattern of solicited AEs was observed across adjuvant systems. Pain was the most prevalent AE, but often mild and of short duration. No increased risks were found for unsolicited AEs, febrile convulsions, potential immune mediated diseases and new onset of chronic diseases.

CONCLUSIONS

Our meta-analysis did not show any safety concerns in clinical trials of the newly adjuvanted vaccines in children ≤10 years of age. An unexplained increase of meningitis in one Phase III AS01-adjuvanted malaria trial and the link between narcolepsy and the AS03-adjuvanted pandemic vaccine illustrate that continued safety monitoring is warranted.

Immunogenicity and safety of cell-derived MF59®-adjuvanted A/H1N1 influenza vaccine for children

Mass immunization of children has the potential to decrease infection rates and prevent the transmission of influenza. We evaluated the immunogenicity, safety, and tolerability of different formulations of cell-derived MF59-adjuvanted and nonadjuvanted A/H1N1 influenza vaccine in children and adolescents. This was a randomized, single-blind, multicenter study with a total of 666 healthy subjects aged 6 months-17 y in one of 3 vaccination groups, each receiving formulations containing different amounts of influenza A/H1N1 antigen with or without MF59. A booster trivalent seasonal MF59 vaccine was administered one year after primary vaccinations. Antibody titers were assessed by hemagglutination inhibition (HI) and microneutralization assays obtained on days 1, 22, 43, 366, and 387 (3 weeks post booster). Safety was monitored throughout the study. One vaccination with 3.75 μg of A/H1N1 antigen formulated with 50% MF59 (3.75_halfMF59) or 7.5 μg of A/H1N1 antigen formulated with 100% MF59 (7.5_fullMF59) induced an HI titer ≥1:40 in >70% of children in the 1-<3, 3-8, and 9-17 y cohorts; however, 2 vaccinations with nonadjuvanted 15 μg A/H1N1 antigen were needed to achieve this response in the 1-<3 and 3-8 y cohorts. Among children aged 6-11 months, 1 dose of 7.5_fullMF59 resulted in an HI titer ≥1:40 in >70% while 2 doses of 3.75_halfMF59 were required to achieve this result. All vaccines were well tolerated. Our findings support the immunogenicity and safety of the 3.75_halfMF59 (2 doses for children <12 months) and 7.5_fullMF59 vaccine formulations for use in children and adolescents aged 6 months to 17 y The use of the 3.75_halfMF59 could have the benefit of antigen and adjuvant sparing, increasing the available vaccine doses allowing vaccination of more people.

Matrix-M™ adjuvation broadens protection induced by seasonal trivalent virosomal influenza vaccine

Background

Influenza virus infections are responsible for significant morbidity worldwide and therefore it remains a high priority to develop more broadly protective vaccines. Adjuvation of current seasonal influenza vaccines has the potential to achieve this goal.

Methods

To assess the immune potentiating properties of Matrix-M™, mice were immunized with virosomal trivalent seasonal vaccine adjuvated with Matrix-M™. Serum samples were isolated to determine the hemagglutination inhibiting (HAI) antibody titers against vaccine homologous and heterologous strains. Furthermore, we assess whether adjuvation with Matrix-M™ broadens the protective efficacy of the virosomal trivalent seasonal vaccine against vaccine homologous and heterologous influenza viruses.

Results

Matrix-M™ adjuvation enhanced HAI antibody titers and protection against vaccine homologous strains. Interestingly, Matrix-M™ adjuvation also resulted in HAI antibody titers against heterologous influenza B strains, but not against the tested influenza A strains. Even though the protection against heterologous influenza A was induced by the adjuvated vaccine, in the absence of HAI titers the protection was accompanied by severe clinical scores and body weight loss. In contrast, in the presence of heterologous HAI titers full protection against the heterologous influenza B strain without any disease symptoms was obtained.

Conclusion

The results of this study emphasize the promising potential of a Matrix-M™-adjuvated seasonal trivalent virosomal influenza vaccine. Adjuvation of trivalent virosomal vaccine does not only enhance homologous protection, but in addition induces protection against heterologous strains and thus provides overall more potent and broad protective immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-015-0435-9) contains supplementary material, which is available to authorized users.

Safety and Immunogenicity of Full-Dose Trivalent Inactivated Influenza Vaccine (TIV) Compared With Half-Dose TIV Administered to Children 6 Through 35 Months of Age

BACKGROUND

Children 6 through 35 months of age are recommended to receive half the dose of influenza vaccine compared with older children and adults.

METHODS

This was a 6-site, randomized 2:1, double-blind study comparing full-dose (0.5 mL) trivalent inactivated influenza vaccine (TIV) with half-dose (0.25 mL) TIV in children 6 through 35 months of age. Children previously immunized with influenza vaccine (primed cohort) received 1 dose, and those with no previous influenza immunizations (naive cohort) received 2 doses of TIV. Local and systemic adverse events were recorded. Sera were collected before immunization and 1 month after last dose of TIV. Hemagglutination inhibition antibody testing was performed.

RESULTS

Of the 243 subjects enrolled (32 primed, 211 naive), data for 232 were available for complete analysis. No significant differences in local or systemic reactions were observed. Few significant differences in immunogenicity to the 3 vaccine antigens were noted. The immune response to H1N1 was significantly higher in the full-dose group among primed subjects. In the naive cohort, the geometric mean titer for all 3 antigens after 2 doses of TIV were significantly higher in the 12 through 35 months compared with the 6 through 11 months age group.

CONCLUSIONS

Our study confirms the safety of full-dose TIV given to children 6 through 35 months of age. An increase in antibody responses after full- versus half-dose TIV was not observed, except for H1N1 in the primed group. Larger studies are needed to clarify the potential for improved immunogenicity with higher vaccine doses. Recommending the same dose could simplify the production, storage, and administration of influenza vaccines.

Systematic review of fever, febrile convulsions and serious adverse events following administration of inactivated trivalent influenza vaccines in children

In 2010, increased febrile convulsions (FC) occurred after administration of inactivated trivalent influenza vaccine (TIV) in Australia. We systematically reviewed the rates of fever, FC and serious adverse events (SAEs) after TIV, focussing on published and unpublished clinical trial data from 2005 to 2012, and performed meta-analysis of fever rates. From 4,372 records in electronic databases, 18 randomised controlled trials (RCTs), 14 non-randomised clinical trials, six observational studies and 12 registered trials (five RCTs and seven non-randomised) were identified. In published RCTs, fever ≥ 38 °C rates after first dose of non-adjuvanted TIV were 6.7% and 6.9% for children aged 6–35 months and ≥ 3 years, respectively. Analysis of RCTs by vaccine manufacturer showed pooled fever estimates up to 5.1% with Sanofi or GlaxoSmithKline vaccines; bioCSL vaccines were used in two non-randomised clinical trials and one unpublished RCT and were associated with fever in 22.5–37.1% for children aged 6–35 months. In RCTs, FCs occurred at a rate of 1.1 per 1,000 vaccinated children. While most TIVs induced acceptably low fever rates, bioCSL influenza vaccines were associated with much higher rates of fever in young children. Future standardised study methodology and access to individual level data would be illuminating.

Current and next generation influenza vaccines: Formulation and production strategies

Vaccination is the most effective method to prevent influenza infection. However, current influenza vaccines have several limitations. Relatively long production times, limited vaccine capacity, moderate efficacy in certain populations and lack of cross-reactivity are important issues that need to be addressed. We give an overview of the current status and novel developments in the landscape of influenza vaccines from an interdisciplinary point of view. The feasibility of novel vaccine concepts not only depends on immunological or clinical outcomes, but also depends on biotechnological aspects, such as formulation and production methods, which are frequently overlooked. Furthermore, the next generation of influenza vaccines is addressed, which hopefully will bring cross-reactive influenza vaccines. These developments indicate that an exciting future lies ahead in the influenza vaccine field.

Influenza virus prevalence in asymptomatic and symptomatic subjects during pandemic and postpandemic periods

BACKGROUND

In 2009, Influenza A(H1N1)pdm09 had a major effect on global health, causing thousands of deaths. However, the results of asymptomatic infection in transmission has not been well studied. We analyzed asymptomatic influenza infection in individuals with different risk factors for acquiring influenza in a university hospital.

METHODS

Respiratory samples from 100 children with respiratory symptoms, their asymptomatic caregivers, 100 asymptomatic HIV-infected patients, and 100 health care workers collected during 2009-2011 were tested for influenza by real time real-time polymerase chain reaction.

RESULTS

Influenza infection rate in symptomatic children was 44% and in asymptomatic adults it was 8.3% (P < .01). Children older than age 5 years had a 3.4 times greater chance of being infected during influenza season than younger children. Among the asymptomatic group, influenza was more frequent in caregivers (14%; P = .032) and a higher rate (31.8%) was observed if a child was infected during the 2009 pandemic. Contact with an infected child was an important risk factor for influenza acquisition (odds ratio, 3.8; 95% confidence interval, 1.1-13.2) among caregivers. The mean cluster of differentiation 4 T-cell count of HIV-positive patients infected with influenza was not statistically different from uninfected patients (P = .29).

CONCLUSIONS

Asymptomatic household contacts of symptomatic children may play an important role in community transmission and a more proactive intervention should be considered during future pandemics.

Influenza vaccination in pediatric age

To increase the protective efficacy against influenza in pediatric populations, several attempts to modify the composition or the route of administration of an inactivated influenza vaccine have been made. Adjuvants have been added, vaccines with higher antigen content have been developed and intradermal administration of inactivated influenza vaccine with a variety of devices has been considered. Such attempts to develop universal influenza vaccines will continue to be made. For some time, the knowledge that the licensed influenza vaccines induce strain-specific immunity and may have low efficacy in unexpected outbreaks of new epidemic strains has motivated the development of preparations with broader and longer-lasting protection. Ideally, children would be included early in the evaluation of the efficacy of new vaccines to avoid lengthy delays in making the protection available to this vulnerable population. Moreover, further studies to clarify definitively whether protection of infants <6 months of age can be obtained through vaccination of the pregnant woman have to be performed.

Dissecting the immune response to MF59-adjuvanted and nonadjuvanted seasonal influenza vaccines in children less than three years of age

INTRODUCTION

Annual seasonal influenza epidemics are particularly dangerous for the very young, the elderly and chronically ill individuals, in whom infection can cause severe morbidity, hospitalization and death. Existing, nonadjuvanted influenza vaccines exhibit a suboptimal immunogenicity and efficacy in immunologically naive subjects such as young children.

METHODS

This phase II, randomized clinical trial was conducted to evaluate the antibody and cell-mediated responses to a trivalent influenza vaccine administered without adjuvant (TIV) or adjuvanted with MF59 (ATIV) in previously nonvaccinated children less than 3 years of age.

RESULTS

The MF59-adjuvanted vaccine was well tolerated, and induced higher titers of hemagglutination inhibition antibodies able to recognize strains different from the one used in the vaccine (heterovariant) than TIV. The presence of the adjuvant MF59 induced a larger expansion of vaccine-specific CD4 T cells. Interestingly, the adjuvant MF59 did not modify the cytokine profile of the elicited T cells, characterized by the production of IL-2 and TNF-α, and did not bias the response toward either Th1 or Th2. The advantage of ATIV over TIV was more pronounced for the virus strains that had not circulated in the years that preceded this study and for the heterovariant strains.

CONCLUSION

These data highlight the relevant role played by the oil-in-water adjuvant MF59 in enhancing the immunogenicity of inactivated influenza vaccines in immunologically naive individuals.

Immunogenicity and tolerability of an MF59-adjuvanted, egg-derived, A/H1N1 pandemic influenza vaccine in children 6-35 months of age

BACKGROUND

Vaccines against pandemic A/H1N1 influenza should provide protective immunity in children, because they are at greater risk of disease than adults. This study was conducted to identify the optimal dose of an MF59®-adjuvanted, egg-derived, A/H1N1 influenza vaccine for young children.

METHODS

Children 6-11 months (N = 144) and 12-35 months (N = 186) of age received vaccine formulations containing either 3.75 μg antigen with half the standard dose of MF59 or 7.5 μg antigen with a standard dose of MF59, or a nonadjuvanted formulation containing 15 μg antigen (children 12-35 months only). Participants were given 2 primary vaccine doses 3 weeks apart, followed by 1 booster dose of MF59-adjuvanted seasonal influenza vaccine 1 year later. Immunogenicity was assessed by hemagglutination inhibition and microneutralization assays.

RESULTS

All vaccine formulations were highly immunogenic and met all 3 European licensure criteria after 2 doses. MF59-adjuvanted vaccines met all licensure criteria after 1 dose in both age cohorts, while nonadjuvanted vaccine did not meet all criteria after 1 dose in children 12-35 months. A single booster dose was highly immunogenic, and stable antibody persistence was observed in response to all vaccines. All vaccines were well tolerated.

CONCLUSIONS

In this study, a single dose of 3.75 μg antigen with half the standard dose of MF59 was shown to be optimal, providing adequate levels of immediate and long-term antibodies in pediatric subjects 6-35 months of age. These data demonstrated that MF59 adjuvant allowed for reduced antigen content and promoted significant long-term antibody persistence in children, with a satisfactory safety profile.