Direct comparison of an inactivated subvirion influenza A virus subtype H5N1 vaccine administered by the intradermal and intramuscular routes

Microneedles: An Emerging Vaccine Delivery Tool and a Prospective Solution to the Challenges of SARS-CoV-2 Mass Vaccination

Vaccination is an effective measure to prevent infectious diseases. Protective immunity is induced when the immune system is exposed to a vaccine formulation with appropriate immunogenicity. However, traditional injection vaccination is always accompanied by fear and severe pain. As an emerging vaccine delivery tool, microneedles overcome the problems associated with routine needle vaccination, which can effectively deliver vaccines rich in antigen-presenting cells (APCs) to the epidermis and dermis painlessly, inducing a strong immune response. In addition, microneedles have the advantages of avoiding cold chain storage and have the flexibility of self-operation, which can solve the logistics and delivery obstacles of vaccines, covering the vaccination of the special population more easily and conveniently. Examples include people in rural areas with restricted vaccine storage facilities and medical professionals, elderly and disabled people with limited mobility, infants and young children afraid of pain. Currently, in the late stage of fighting against COVID-19, the main task is to increase the coverage of vaccines, especially for special populations. To address this challenge, microneedle-based vaccines have great potential to increase global vaccination rates and save many lives. This review describes the current progress of microneedles as a vaccine delivery system and its prospects in achieving mass vaccination against SARS-CoV-2.

Challenges in the Vaccination of the Elderly and Strategies for Improvement

In recent years, the elderly has become a rapidly growing proportion of the world's population as life expectancy is extending. Immunosenescence and inflammaging contribute to the increased risk of chronic non-communicable and acute infectious diseases. Frailty is highly prevalent in the elderly and is associated with an impaired immune response, a higher propensity to infection, and a lower response to vaccines. Additionally, the presence of uncontrolled comorbid diseases in the elderly also contributes to sarcopenia and frailty. Vaccine-preventable diseases that threaten the elderly include influenza, pneumococcal infection, herpes zoster, and COVID-19, which contribute to significant disability-adjusted life years lost. Previous studies had shown that conventional vaccines only yielded suboptimal protection that wanes rapidly in a shorter time. This article reviews published papers on several vaccination strategies that were developed for the elderly to solve these problems: more immunogenic vaccine formulations using larger doses of antigen, stronger vaccine adjuvants, recombinant subunit or protein conjugated vaccines, newly developed mRNA vaccines, giving booster shots, and exploring alternative routes of administration. Included also are several publications on senolytic medications under investigation to boost the immune system and vaccine response in the elderly. With all those in regard, the currently recommended vaccines for the elderly are presented.

Broadly Reactive IgG Responses to Heterologous H5 Prime-Boost Influenza Vaccination Are Shaped by Antigenic Relatedness to Priming Strains

Prime-boost vaccinations of humans with different H5 strains have generated broadly protective antibody levels. However, the effect of an individual’s H5 exposure history on antibody responses to subsequent H5 vaccination is poorly understood. To investigate this, we analyzed the IgG responses to H5 influenza A/Indonesia/5/2005 (Ind05) virus vaccination in three cohorts: (i) a doubly primed group that had received two H5 virus vaccinations, namely, against influenza A/Vietnam/203/2004 (Vie04) virus 5 years prior and A/Hong Kong/156/1997 (HK97) 11 years prior to the Ind05 vaccination; (ii) a singly primed group that had received a vaccination against Vie04 virus 5 years prior to the Ind05 vaccination; and (iii) an H5-naive group that received two doses of the Ind05 vaccine 28 days apart. Hemagglutinin (HA)-reactive IgG levels were estimated by a multiplex assay against an HA panel that included 21 H5 strains and 9 other strains representing the H1, H3, H7, and H9 subtypes. Relative HA antibody landscapes were generated to quantitatively analyze the magnitude and breadth of antibody binding after vaccination. We found that short-interval priming and boosting with the Ind05 vaccine in the naive group generated a low anti-H5 response. Both primed groups generated robust antibody responses reactive to a broad range of H5 strains after receiving a booster injection of Ind05 vaccine; IgG antibody levels persisted longer in subjects who had been doubly primed years ago. Notably, the IgG responses were strongest against the first priming H5 strain, which reflects influenza virus immune imprinting. Finally, the broad anti-H5 IgG response was stronger against strains having a small antigenic distance from the initial priming strain.

Vaccine delivery alerts innate immune systems for more immunogenic vaccination

Vaccine delivery technologies are mainly designed to minimally invasively deliver vaccines to target tissues with little or no adjuvant effects. This study presents a prototype laser-based powder delivery (LPD) with inherent adjuvant effects for more immunogenic vaccination without incorporation of external adjuvants. LPD takes advantage of aesthetic ablative fractional laser to generate skin microchannels to support high-efficient vaccine delivery and at the same time creates photothermal stress in microchannel-surrounding tissues to boost vaccination. LPD could significantly enhance pandemic influenza 2009 H1N1 vaccine immunogenicity and protective efficacy as compared with needle-based intradermal delivery in murine models. The ablative fractional laser was found to induce host DNA release, activate NLR family pyrin domain containing 3 inflammasome, and stimulate IL-1β release despite their dispensability for laser adjuvant effects. Instead, the ablative fractional laser activated MyD88 to mediate its adjuvant effects by potentiation of antigen uptake, maturation, and migration of dendritic cells. LPD also induced minimal local or systemic adverse reactions due to the microfractional and sustained vaccine delivery. Our data support the development of self-adjuvanted vaccine delivery technologies by intentional induction of well-controlled tissue stress to alert innate immune systems for more immunogenic vaccination.

Effect of recent seasonal influenza vaccination on serum antibody responses to candidate pandemic influenza A/H5N1 vaccines: A meta-analysis

Recent studies have suggested that among those receiving seasonal influenza vaccine (SIV), reduced immunogenicity is observed in recently vaccinated (RV; within the past season or 2) persons when compared with those not recently vaccinated (NRV). We performed a meta-analysis to assess the effect of recent immunization with SIV on serum H5 hemagglutination inhibition (HAI) antibody responses after influenza A/H5N1 vaccination using data from a series of randomized controlled trials. The primary outcome was seroconversion measured by HAI assays following receipt of 2 doses of H5N1 vaccine. The geometric mean titer (GMT) of serum HAI antibody after vaccination was the secondary outcome. Analyses were performed using propensity score (PS) matching. The PS for each individual in the meta-analysis cohort was calculated using logistic regression and covariates included age, gender, race, antigen dose, adjuvant, statin use and vaccine manufacturer. 2015 subjects enrolled in 7 clinical trials were eligible for inclusion in the meta-analysis cohort; among these, 915 (45%) were RV. 901 RV subjects were matched (1:1) with replacement to a subject who was NRV. Subjects who received SIV within the previous season were significantly less likely to seroconvert following H5N1 vaccination (adjusted odds ratio 0.76; 95%CI 0.60-0.96; p = 0.024), and the GMT was 18% higher among NRV subjects (GM ratio of HAI antibody 1.18; 95%CI 1.04-1.33; p = 0.008). Further work is needed to better define the effects of, and mechanisms contributing to, reduced immune responses to H5N1 vaccine among RV subjects.

Pandemic influenza vaccines: what they have taught us about B cell immunology

The emergence of avian influenza viruses stimulated pandemic concerns and efforts to develop protective vaccines. Studies of the immune responses to experimental vaccines for pandemic influenza have taught us lessons about human immunity to influenza in general that can be applied to seasonal, pandemic, and even universal vaccine responses. For example, the concepts of targeting the hemagglutinin stalk and elicitation of stalk reactive antibodies grew out of studies of the 2009 pandemic H1N1 vaccines. More recently, the phenomenon of imprinting, the influence of early life exposure to influenza modifying responses to the viruses or vaccines later in life, has been reinforced through the study of potential pandemic influenza virus vaccines such as H7N9. These studies have also revealed potential strategies to improve responses to novel influenza strains and produce more broadly cross-reactive B cell and antibody responses. These concepts are discussed in detail in this review.

Fighting against a protean enemy: immunosenescence, vaccines, and healthy aging

The progressive increase of the aged population worldwide mandates new strategies to ensure sustained health and well-being with age. The development of better and/or new vaccines against pathogens that affect older adults is one pivotal intervention in approaching this goal. However, the functional decline of various physiological systems, including the immune system, requires novel approaches to counteract immunosenescence. Although important progress has been made in understanding the mechanisms underlying the age-related decline of the immune response to infections and vaccinations, knowledge gaps remain, both in the areas of basic and translational research. In particular, it will be important to better understand how environmental factors, such as diet, physical activity, co-morbidities, and pharmacological treatments, delay or contribute to the decline of the capability of the aging immune system to appropriately respond to infectious diseases and vaccination. Recent findings suggest that successful approaches specifically targeted to the older population can be developed, such as the high-dose and adjuvanted vaccines against seasonal influenza, the adjuvanted subunit vaccine against herpes zoster, as well as experimental interventions with immune-potentiators or immunostimulants. Learning from these first successes may pave the way to developing novel and improved vaccines for the older adults and immunocompromised. With an integrated, holistic vaccination strategy, society will offer the opportunity for an improved quality of life to the segment of the population that is going to increase most significantly in numbers and proportion over future decades.

Priming Vaccination With Influenza Virus H5 Hemagglutinin Antigen Significantly Increases the Duration of T cell Responses Induced by a Heterologous H5 Booster Vaccination

BACKGROUND

Influenza A(H5N1) virus and other avian influenza virus strains represent major pandemic threats. Like all influenza A virus strains, A(H5N1) viruses evolve rapidly. Innovative immunization strategies are needed to induce cross-protective immunity.

METHODS

Subjects primed with clade 1 H5 antigen, with or without adjuvant, and H5-naive individuals were boosted with clade 2 H5 antigen. The impact of priming on T cells capable of both proliferation and cytokine production after antigen restimulation was assessed.

RESULTS

Subjects previously vaccinated with clade 1 H5 antigen developed significantly enhanced clade 2 H5 cross-reactive T cell responses detectable 6 months after vaccination with clade 2 H5 antigen. Priming dose (15 µg vs 45 or 90 µg) had no effect on magnitude of heterotypic H5 T cell responses. In contrast, age at priming negatively modulated both the magnitude and duration of heterotypic H5 T cell responses. Elderly subjects developed significantly less heterotypic H5 T cell boosting, predominantly for T cells capable of cytokine production. Adjuvant had a positive albeit weaker effect than age. The magnitude of CD4(+) interferon-γ producing T cells correlated with H5 antibody responses.

CONCLUSIONS

H5 heterotypic priming prior to onset of an A(H5N1) pandemic may increase magnitude and duration of immunity against a newly drifted pandemic H5 virus.

Local innate immune responses in the vaccine adjuvant-injected muscle

Inducing a high magnitude of antibodies, possibly in combination with T-cell responses that offer epitope breadth over prolonged periods of time is likely a prerequisite for effective vaccines against severe diseases such as HIV-1 infection, malaria and tuberculosis. A much better understanding of the innate immune mechanisms that are critical for inducing desired responses to vaccination would help in the design of novel vaccines. The majority of human vaccines are administered into the muscle. In this brief review, we focus on the initial innate immune events that occur locally at the site of intramuscular vaccine delivery, and how they are influenced by clinically approved vaccine adjuvants. In particular, the effects on cell mobilization, cell activation and vaccine antigen uptake are reviewed. Understanding how distinct adjuvants enhance and tailor vaccine responses would facilitate the selection of the best-suited adjuvant to improve vaccine efficacy to a given pathogen.

Cell mediated immune responses following revaccination with an influenza A/H5N1 vaccine

PURPOSE

The study aims were to determine whether inactivated influenza A/H5N1 vaccine administration elicited cell mediated immune (CMI) responses and the impact of adjuvant, vaccine dose and subject age on these responses.

METHODS

Adults who were previously primed with either adjuvanted or unadjuvanted, inactivated, A/H5N1/Vietnam/1203/2004 (Clade 1) vaccine or unprimed (received placebo) in previous vaccine studies were randomized to receive one (primed) or two (unprimed) 15- or 90-mcg doses of inactivated, A/H5N1/Indonesia/05/05 (Clade 2) vaccine. Peripheral blood mononuclear cells (PBMCs) were collected and analyzed from a subset of vaccinees to assess CMI responses using IFN-γ and granzyme B ELISPOT assays. Cytokine measurements were performed on PBMC supernatants after stimulation with H5N1 virus.

RESULTS

PBMCs were available from 177 participants; 88 and 89 received 15-mcg and 90-mcg of unadjuvanted clade 2 vaccine, respectively. Following H5N1 clade 1 stimulation, IFN-γ but not granzyme B normalized spot-forming cell numbers had statistically significant increased numbers at each of the post-vaccination timepoints compared to baseline in pooled analyses of all vaccine doses and age groups. Clade 2 stimulation resulted in statistically significant increased numbers of IFN-γ cells only 180 days following the last vaccination. Responses were similar among younger and older study participants, as were responses among those primed with alum-adjuvanted or non-adjuvanted clade 1 H5N1 vaccines. The dosage of clade 2 vaccine did not impact CMI responses among primed subjects, but responses were statistically significantly greater in unprimed recipients of the 90-mcg dosage compared to unprimed recipients of the 15-mcg dosage. IFN-γ levels in the supernatants of stimulated PBMC were strongly correlated with IFN-γ ELISPOT results.

CONCLUSION

CMI responses occur in adults administered influenza A/H5N1 inactivated influenza vaccine.

Effect of receptor binding specificity on the immunogenicity and protective efficacy of influenza virus A H1 vaccines

The biological basis for the poor immunogenicity of unadjuvanted avian influenza A virus vaccines in mammals is not well understood. Here, we mutated the hemagglutinin (HA) of two H1N1 virus vaccines to determine whether virus receptor binding specificity contributes to the low immunogenicity of avian influenza virus vaccines. Mutations were introduced into the HA of an avian influenza virus, A/Duck/New York/15024-21/96 (Dk/96) which switched the binding preference from α2,3- to α2,6-linked sialic acid (SA). A switch in receptor specificity of the human A/South Carolina/1/18 (SC/18) virus generated a mutant virus with α2,3 SA (avian) binding preference. Inactivated vaccines were generated and administered to mice and ferrets intramuscularly. We found that the vaccines with human receptor binding preference induced slightly higher antibody titers and cell-mediated immune responses compared to their isogenic viruses with avian receptor binding specificity. Upon challenge with DK/96 or SC18 virus, differences in lung virus titers between the vaccine groups with different receptor-binding specificities were minimal. Overall, our data suggest that receptor binding specificity contributes only marginally to the immunogenicity of avian influenza vaccines and that other factors may also be involved.

Vaccine strategies to enhance immune responses in the aged

The elderly population is more susceptible to infections with higher risks of morbidity and mortality. This is caused by the accumulation of immune defects with aging. The best way to protect people against infections is vaccination. Unfortunately, the same immune defects that render the elderly susceptible to infectious diseases also prevent the development of protective immunity following immunization. A good example of this is the influenza vaccine that only protects between 40 and 60% of the vaccinees over 65 years. In the past decade, tremendous efforts have been put toward improving the influenza vaccine for the elderly. We therefore use this example to present various strategies employed to overcome these age-associated immune defects and hence make vaccines more efficacious for the aged.

Cross-protection against drifted influenza viruses: options offered by adjuvanted and intradermal vaccines

Antigenic drift, the evolutionary mechanism of influenza viruses, results in an increased susceptibility of vaccinated subjects against circulating viruses. New vaccines able to grant a broader and cross-reactive immune response against drifted influenza variants are needed. Several strategies were explored to enhance the immunogenicity of plain vaccines: adjuvants, carriers and intradermal administration of influenza vaccine emerge as a promising options. To evaluate the ability of a MF59-adjuvanted and intradermal influenza vaccine to elicit an effective antibody response against circulating viruses presenting antigenic patterns different from those of the vaccine strains, we compared antibody responses elicited by "implemented" vaccines and conventional intramuscular trivalent inactivated vaccine against heterologous circulating influenza A viruses. Different studies, simulating different epidemiological pictures produced by the natural antigenic drift of seasonal influenza viruses, highlighted the superior cross-reactivity of the antibodies elicited by MF59 and intradermal vaccines, compared with subunit or split vaccine against heterologous viruses.

Evaluations for in vitro correlates of immunogenicity of inactivated influenza a H5, H7 and H9 vaccines in humans

Background

Serum antibody responses in humans to inactivated influenza A (H5N1), (H9N2) and A (H7) vaccines have been varied but frequently low, particularly for subunit vaccines without adjuvant despite hemagglutinin (HA) concentrations expected to induce good responses.

Design

To help understand the low responses to subunit vaccines, we evaluated influenza A (H5N1), (H9N2), (H7N7) vaccines and 2009 pandemic (H1N1) vaccines for antigen uptake, processing and presentation by dendritic cells to T cells, conformation of vaccine HA in antibody binding assays and gel analyses, HA titers with different red blood cells, and vaccine morphology in electron micrographs (EM).

Results

Antigen uptake, processing and presentation of H5, H7, H9 and H1 vaccine preparations evaluated in humans appeared normal. No differences were detected in antibody interactions with vaccine and matched virus; although H7 trimer was not detected in western blots, no abnormalities in the conformation of the HA antigens were identified. The lowest HA titers for the vaccines were <1∶4 for the H7 vaccine and 1∶661 for an H9 vaccine; these vaccines induced the fewest antibody responses. A (H1N1) vaccines were the most immunogenic in humans; intact virus and virus pieces were prominent in EM. A good immunogenic A (H9N2) vaccine contained primarily particles of viral membrane with external HA and NA. A (H5N1) vaccines intermediate in immunogenicity were mostly indistinct structural units with stellates; the least immunogenic A (H7N7) vaccine contained mostly small 5 to 20 nm structures.

Summary

Antigen uptake, processing and presentation to human T cells and conformation of the HA appeared normal for each inactivated influenza A vaccine. Low HA titer was associated with low immunogenicity and presence of particles or split virus pieces was associated with higher immunogenicity.