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

Tissue-specific sex differences in pediatric and adult immune cell composition and function

Sex-based differences in immune cell composition and function can contribute to distinct adaptive immune responses. Prior work has quantified these differences in peripheral blood, but little is known about sex differences within human lymphoid tissues. Here, we characterized the composition and phenotypes of adaptive immune cells from male and female ex vivo tonsils and evaluated their responses to influenza antigens using an immune organoid approach. In a pediatric cohort, female tonsils had more memory B cells compared to male tonsils direct ex vivo and after stimulation with live-attenuated but not inactivated vaccine, produced higher influenza-specific antibody responses. Sex biases were also observed in adult tonsils but were different from those measured in children. Analysis of peripheral blood immune cells from in vivo vaccinated adults also showed higher frequencies of tissue homing CD4 T cells in female participants. Together, our data demonstrate that distinct memory B and T cell profiles are present in male vs. female lymphoid tissues and peripheral blood respectively and suggest that these differences may in part explain sex biases in response to vaccines and viruses.

Sex Differences in the Immunogenicity and Efficacy of Seasonal Influenza Vaccines: A Meta-analysis of Randomized Controlled Trials

Background

Sex impacts individuals' response to vaccination. However, most vaccine studies do not report these differences disaggregated by sex. The aim of this study was to assess sex differences in the immunogenicity and efficacy of influenza vaccine.

Methods

We performed a meta-analysis using phase 3 randomized controlled trial data conducted between 2010 and 2018. Using hemagglutination inhibition antibody titers for each strain, differences in geometric mean ratios (GMRs) were calculated by sex. Risk ratios (RRs) comparing seroconversion proportions were pooled for females and males using random-effects models. Vaccine efficacy (VE) was assessed. Data were analyzed by age group (18-64 vs ≥65 years).

Results

A total of 33 092 healthy adults from 19 studies were included for immunogenicity analysis, and 6740 from 1 study for VE. Whereas no sex differences in immunogenicity were found in adults <65 years old, older females had a significantly greater chance to seroconvert compared to older males for all strains: RRH1N1 = 1.17 [95% confidence interval {CI}, 1.12-1.23]; RRH3N2 = 1.09 [95% CI, 1.05-1.14]; RRVictoria = 1.23 [95% CI, 1.14-1.31]; RRYamagata = 1.22 [95% CI, 1.14-1.30]. GMRs were also higher in older females for all strains compared to older males. VE in preventing laboratory-confirmed influenza was higher in older females compared to older males with VEs of 27.32% (95% CI, 1.15%-46.56%) and 6.06% (95% CI, -37.68% to 35.90%), respectively.

Conclusions

Our results suggest a higher immunogenicity and VE in females compared to males in older adults. These differences in immunogenicity and VE support the disaggregation of vaccine data by sex in clinical trials and observational studies.

Clinical Trials Registration

CRD42018112260.

Antibody titres elicited by the 2018 seasonal inactivated influenza vaccine decline by 3 months post-vaccination but persist for at least 6 months

BACKGROUND

In Australia, seasonal inactivated influenza vaccine is typically offered in April. However, the onset, peak and end of a typical influenza season vary, and optimal timing for vaccination remains unclear. Here, we investigated vaccine-induced antibody response kinetics over 6 months in different age groups.

METHODS

We conducted a prospective serosurvey among 71 adults aged 18-50 years, 15 community-dwelling ('healthy') and 16 aged-care facility resident ('frail') older adults aged ≥65 years who received the 2018 southern hemisphere vaccines. Sera were collected at baseline, and 1, 2, 4, and 6 months post-vaccination. Antibody titres were measured by haemagglutination inhibition or microneutralisation assays. Geometric mean titres were estimated using random effects regression modelling and superimposed on 2014-2018 influenza season epidemic curves.

RESULTS

Antibody titres peaked 1.2-1.3 months post-vaccination for all viruses, declined by 3 months post-vaccination but, notably, persisted above baseline after 6 months in all age groups by 1.3- to 1.5-fold against A(H1N1)pdm09, 1.7- to 2-fold against A(H3N2), 1.7- to 2.1-fold against B/Yamagata and 1.8-fold against B/Victoria. Antibody kinetics were similar among different age groups. Antibody responses were poor against cell-culture grown compared to egg-grown viruses.

CONCLUSIONS

These results suggest subtype-specific antibody-mediated protection persists for at least 6 months, which corresponds to the duration of a typical influenza season.

Systems Biological Analysis of Immune Response to Influenza Vaccination

The last decade has witnessed tremendous progress in immunology and vaccinology, owing to several scientific and technological breakthroughs. Systems vaccinology is a field that has emerged at the forefront of vaccine research and development and provides a unique way to probe immune responses to vaccination in humans. The goals of systems vaccinology are to use systems-based approaches to define signatures that can be used to predict vaccine immunogenicity and efficacy and to delineate the molecular mechanisms driving protective immunity. The application of systems biological approaches in influenza vaccination studies has enabled the discovery of early signatures that predict immunogenicity to vaccination and yielded novel mechanistic insights about vaccine-induced immunity. Here we review the contributions of systems vaccinology to influenza vaccine development and critically examine the potential of systems vaccinology toward enabling the development of a universal influenza vaccine that provides robust and durable immunity against diverse influenza viruses.

Age-Specific Incidence of Influenza A Responds to Change in Virus Subtype Dominance

When H3N2 replaced H1N1 as the dominant influenza A subtype during the 2018-2019 season, the pattern of age-specific incidence shifted due to the lingering effects of antigenic imprinting. The characteristic shape that imprinting leaves on influenza susceptibility could foster important advances in understanding and predicting the epidemiology of influenza.

The Effects of Imprinting and Repeated Seasonal Influenza Vaccination on Adaptive Immunity after Influenza Vaccination

(1) Background: The influenza virus continues to cause significant annual morbidity and mortality. The overall efficacy of seasonal influenza vaccination is suboptimal, which is partly due to host immune factors. The effects of imprinting and repeated seasonal influenza vaccination were investigated to assess for immune factors and mechanisms that impact influenza vaccine responses. (2) Methods: Twenty participants were enrolled into a prospective pilot study based on birth cohort and seasonal influenza immunization history. Immunologic parameters were assessed over a six-month period after the seasonal influenza vaccine was administered. (3) Results: There was no significant imprinting effect, as measured by hemagglutination inhibition (HAI) fold change, HAI geometric mean titer (GMT) for Day 29 or Day 180 post-vaccination and antigen- specific antibody-secreting cells (ASC) for Day 8 post-vaccination. Individuals who had minimal prior seasonal influenza vaccination had a higher magnitude ASC response and a higher HAI fold change post-vaccination than individuals who were repeatedly vaccinated. (4) Conclusions: Repeated seasonal influenza vaccination resulted in a decreased fold change of the immune response, although individuals in this cohort tended to have high HAI titers at baseline that persisted after vaccination. Imprinting effects were not observed in this cohort. These host immune factors should be considered in the development of universal influenza vaccines. ClinicalTrials.gov Identifier: NCT03686514.

Insights from the comparison of genomic variants from two influenza B viruses grown in the presence of human antibodies in cell culture

Understanding the extent and limitation of viral genome evolution can provide insight about potential drug and vaccine targets. Influenza B Viruses (IBVs) infect humans in a seasonal manner and causes significant morbidity and mortality. IBVs are negative-sense single-stranded RNA viruses with a segmented genome and can be divided into two antigenically distinct lineages. The two lineages have been circulating and further evolving for almost four decades. The immune response to IBV infection can lead to antibodies that target the strain causing the infection. Some antibodies are cross-reactive and are able to bind strains from both lineages but, because of antigenic drift and immunodominance, both lineages continue to evolve and challenge human health. Here we investigate changes in the genomes of an IBVs from each lineage after passage in tissue culture in the presence of human sera containing polyclonal antibodies directed toward antigenically and temporally distinct viruses. Our previous analysis of the fourth segment, which encodes the major surface protein HA, revealed a pattern of change in which signature sequences from one lineage mutated to the signature sequences of the other lineage. Here we analyze genes from the other genomic segments and observe that most of the quasispecies’ heterogeneity occurs at the same loci in each lineage. The nature of the variants at these loci are investigated and possible reasons for this pattern are discussed. This work expands our understanding of the extent and limitations of genomic change in IBV.

Immune Pressure on Polymorphous Influenza B Populations Results in Diverse Hemagglutinin Escape Mutants and Lineage Switching

Mutations arise in the genomes of progeny viruses during infection. Mutations that occur in epitopes targeted by host antibodies allow the progeny virus to escape the host adaptive, B-cell mediated antibody immune response. Major epitopes have been identified in influenza B virus (IBV) hemagglutinin (HA) protein. However, IBV strains maintain a seasonal presence in the human population and changes in IBV genomes in response to immune pressure are not well characterized. There are two lineages of IBV that have circulated in the human population since the 1980s, B-Victoria and B-Yamagata. It is hypothesized that early exposure to one influenza subtype leads to immunodominance. Subsequent seasonal vaccination or exposure to new subtypes may modify subsequent immune responses, which, in turn, results in selection of escape mutations in the viral genome. Here we show that while some mutations do occur in known epitopes suggesting antibody escape, many mutations occur in other parts of the HA protein. Analysis of mutations outside of the known epitopes revealed that these mutations occurred at the same amino acid position in viruses from each of the two IBV lineages. Interestingly, where the amino acid sequence differed between viruses from each lineage, reciprocal amino acid changes were observed. That is, the virus from the Yamagata lineage become more like the Victoria lineage virus and vice versa. Our results suggest that some IBV HA sequences are constrained to specific amino acid codons when viruses are cultured in the presence of antibodies. Some changes to the known antigenic regions may also be restricted in a lineage-dependent manner. Questions remain regarding the mechanisms underlying these results. The presence of amino acid residues that are constrained within the HA may provide a new target for universal vaccines for IBV.

Age-associated changes in the impact of sex steroids on influenza vaccine responses in males and females

Vaccine-induced immunity declines with age, which may differ between males and females. Using human sera collected before and 21 days after receipt of the monovalent A/Cal/09 H1N1 vaccine, we evaluated cytokine and antibody responses in adult (18-45 years) and aged (65+ years) individuals. After vaccination, adult females developed greater IL-6 and antibody responses than either adult males or aged females, with female antibody responses being positively associated with concentrations of estradiol. To test whether protection against influenza virus challenge was greater in females than males, we primed and boosted adult (8-10 weeks) and aged (68-70 weeks) male and female mice with an inactivated A/Cal/09 H1N1 vaccine or no vaccine and challenged with a drift variant A/Cal/09 virus. As compared with unvaccinated mice, vaccinated adult, but not aged, mice experienced less morbidity and better pulmonary viral clearance following challenge, regardless of sex. Vaccinated adult female mice developed antibody responses that were of greater quantity and quality and more protective than vaccinated adult males. Sex differences in vaccine efficacy diminished with age in mice. To determine the role of sex steroids in vaccine-induced immune responses, adult mice were gonadectomized and hormones (estradiol in females and testosterone in males) were replaced in subsets of animals before vaccination. Vaccine-induced antibody responses were increased in females by estradiol and decreased in males by testosterone. The benefit of elevated estradiol on antibody responses and protection against influenza in females is diminished with age in both mice and humans.