Roadmap for Sex-Responsive Influenza and COVID-19 Vaccine Research in Older Adults

COVID-19 booster doses reduce sex disparities in antibody responses among nursing home residents

BACKGROUND

Data suggest that antibody responses following COVID-19 vaccines are a correlate of protection. Some studies, including the clinical trials of COVID-19 mRNA vaccines, did not stratify and evaluate whether antibody responses to COVID-19 vaccines differed between the sexes or with aging. This gap in research is particularly relevant for older populations such as nursing home residents (NHR). We hypothesized that sex differences in vaccine-induced antibody responses may intersect with age and be diminished among older adults residing in nursing homes.

METHODS

We analyzed serum samples from 638 NHRs collected serially after the primary two-dose series and three subsequent booster doses of mRNA SARS-CoV-2 vaccinations. We analyzed anti-Spike IgG and neutralizing antibody titers to the Wuhan and Omicron BA.4/5 variant strains. Mixed-effects models predicting log-transformed titers were estimated to compare responses across vaccine doses, focusing on sex-differential responses. For detected post-dose sex differences, additional sample times were analyzed to assess the duration of the difference.

RESULTS

Following the primary series, female NHRs with a prior history of SARS-CoV-2 infection had significantly higher Wuhan anti-Spike antibodies and neutralizing antibody titers than male NHRs with differences persisting up to nine months post-vaccination. Subsequent monovalent booster doses and a bivalent booster dose eliminated this disparity. We did not detect any differential response to the Omicron BA.4/5 variant.

CONCLUSIONS

The blunting of sex differences in antibody response observed following the primary series by the 1st booster dose underscores the importance of booster vaccination in this population.

Independent effects of testosterone, estradiol, and sex chromosomes on gene expression in immune cells of trans- and cisgender individuals

The origins of sex differences in human disease are elusive, in part because of difficulties in separating the effects of sex hormones and sex chromosomes. To separate these variables, we examined gene expression in four groups of trans- or cisgender individuals: XX individuals treated with exogenous testosterone (n=21), XY treated with exogenous estradiol (n=13), untreated XX (n=20), and untreated XY (n=15). We performed single-cell RNA-sequencing of 358,426 peripheral blood mononuclear cells. Across the autosomes, 8 genes responded with a significant change in expression to testosterone, 34 to estradiol, and 32 to sex chromosome complement with no overlap between the groups. No sex-chromosomal genes responded significantly to testosterone or estradiol, but X-linked genes responded to sex chromosome complement in a remarkably stable manner across cell types. Through leveraging a four-state study design, we successfully separated the independent actions of testosterone, estradiol, and sex chromosome complement on genome-wide gene expression in humans.

Mitigating COVID-19 Mortality and Morbidity in China's Aging Population: A Focus on Available Medications and Future Developments

The COVID-19 pandemic, often referred to as the geropandemic, has put immense pressure on global healthcare systems worldwide, leading to a rush in the development and approval of medications for the treatment of the viral infection. Clinical trials on efficacy and safety had a limited spectrum on inclusion and endpoints because of the urgent need for fast results. The chronologically and biologically aged population is especially at risk for severe or lethal disease, as well as treatment-associated toxicity. In China, the growing elderly population segment has been a focus in public health measurements of COVID-19, guiding towards herd immunity with a mild variant, thus minimizing overall deaths and morbidity. While the COVID-19 pandemic has now been reclassified and the virus weakened, there is a clear need for novel therapies to protect the elderly. This paper reviews the current safety and efficacy of available COVID-19 medications in China, with a specific focus on 3CL protease inhibitors and the aging population. The current COVID wave in China has demonstrated a significant impact on the elderly and the need for new drugs that are effective at low doses and can be used alone, without harmful side effects, generation of viral resistance, and drug-drug interactions. The rush to develop and approve COVID-19 medications has brought up important questions about the balance between speed and caution, resulting in a pipeline of novel therapies now moving through clinical trials, including third-generation 3CL protease inhibitors. A majority of those therapeutics are being developed in China.

How Estrogen, Testosterone, and Sex Differences Influence Serum Immunoglobulin Isotype Patterns in Mice and Humans

Females often exhibit superior immune responses compared to males toward vaccines and pathogens such as influenza viruses and SARS-CoV-2. To help explain these differences, we first studied serum immunoglobulin isotype patterns in C57BL/6 male and female mice. We focused on IgG2b, an isotype that lends to virus control and that has been previously shown to be elevated in murine females compared to males. Improvements in IgG2b serum levels, and/or IgG2b ratios with other non-IgM isotypes, were observed when: (i) wildtype (WT) female mice were compared to estrogen receptor knockout mice (IgG2b, IgG2b/IgG3, IgG2b/IgG1, and IgG2b/IgA were all higher in WT mice), (ii) unmanipulated female mice were compared to ovariectomized mice (IgG2b/IgA was higher in unmanipulated animals), (iii) female mice were supplemented with estrogen in the context of an inflammatory insult (IgG2b and IgG2b/IgG3 were improved by estrogen supplementation), and (iv) male mice were supplemented with testosterone, a hormone that can convert to estrogen in vivo (IgG2b, IgG2b/IgG3, IgG2b/IgG1, and IgG2b/IgA were all improved by supplementation). We next examined data from three sets of previously described male and female human blood samples. In each case, there were higher IgG2 levels, and/or ratios of IgG2 with non-IgM isotypes, in human females compared to males. The effects of sex and sex hormones in the mouse and human studies were subtle, but frequent, suggesting that sex hormones represent only a fraction of the factors that influence isotype patterns. Examination of the gene loci suggested that upregulation of murine IgG2b or human IgG2 could be mediated by estrogen receptor binding to estrogen response elements and cytosine-adenine (CA) repeats upstream of respective Cγ genes. Given that murine IgG2b and human IgG2 lend to virus control, the isotype biases in females may be sufficient to improve outcomes following vaccination or infection. Future attention to sex hormone levels, and consequent immunoglobulin isotype patterns, in clinical trials are encouraged to support the optimization of vaccine and drug products for male and female hosts.

Sex-disaggregated outcomes of adverse events after COVID-19 vaccination: A Dutch cohort study and review of the literature

Background

Albeit the need for sex-disaggregated results of adverse events after immunization (AEFIs) is gaining attention since the COVID-19 pandemic, studies with emphasis on sexual dimorphism in response to COVID-19 vaccination are relatively scarce. This prospective cohort study aimed to assess differences in the incidence and course of reported AEFIs after COVID-19 vaccination between males and females in the Netherlands and provides a summary of sex-disaggregated outcomes in published literature.

Methods

Patient reported outcomes of AEFIs over a six month period following the first vaccination with BioNTech-Pfizer, AstraZeneca, Moderna or the Johnson&Johnson vaccine were collected in a Cohort Event Monitoring study. Logistic regression was used to assess differences in incidence of 'any AEFI', local reactions and the top ten most reported AEFIs between the sexes. Effects of age, vaccine brand, comorbidities, prior COVID-19 infection and the use of antipyretic drugs were analyzed as well. Also, time-to-onset, time-to-recovery and perceived burden of AEFIs was compared between the sexes. Third, a literature review was done to retrieve sex-disaggregated outcomes of COVID-19 vaccination.

Results

The cohort included 27,540 vaccinees (38.5% males). Females showed around two-fold higher odds of having any AEFI as compared to males with most pronounced differences after the first dose and for nausea and injection site inflammation. Age was inversely associated with AEFI incidence, whereas a prior COVID-19 infection, the use of antipyretic drugs and several comorbidities were positively associated. The perceived burden of AEFIs and time-to-recovery were slightly higher in females.

Discussion

The results of this large cohort study correspond to existing evidence and contribute to the knowledge gain necessary to disentangle the magnitude of the effect sex in response to vaccination. Whilst females have a significant higher probability of experiencing an AEFI than males, we observed that the course and burden is only to a minor extent different between the sexes.

Impaired CD4+ T cell response in older adults is associated with reduced immunogenicity and reactogenicity of mRNA COVID-19 vaccination

Whether age-associated defects in T cells impact the immunogenicity and reactogenicity of mRNA vaccines remains unclear. Using a vaccinated cohort (n = 216), we demonstrated that older adults (aged ≥65 years) had fewer vaccine-induced spike-specific CD4⁺ T cells including CXCR3⁺ circulating follicular helper T cells and the T_H1 subset of helper T cells after the first dose, which correlated with their lower peak IgG levels and fewer systemic adverse effects after the second dose, compared with younger adults. Moreover, spike-specific T_H1 cells in older adults expressed higher levels of programmed cell death protein 1, a negative regulator of T cell activation, which was associated with low spike-specific CD8⁺ T cell responses. Thus, an inefficient CD4⁺ T cell response after the first dose may reduce the production of helper T cytokines, even after the second dose, thereby lowering humoral and cellular immunity and reducing systemic reactogenicity. Therefore, enhancing CD4⁺ T cell response following the first dose is key to improving vaccine efficacy in older adults.

Sex-Differential and Non-specific Effects of Vaccines Over the Life Course

Biological sex and age have profound effects on immune responses throughout the lifespan and impact vaccine acceptance, responses, and outcomes. Mounting evidence from epidemiological, clinical, and animal model studies show that males and females respond differentially to vaccination throughout the lifespan. Within age groups, females tend to produce greater vaccine-induced immune responses than males, with sex differences apparent across all age groups, but are most pronounced among reproductive aged individuals. Females report more adverse effects following vaccination than males. Females, especially among children under 5 years of age, also experience more non-specific effects of vaccination. Despite these known sex- and age-specific differences in vaccine-induced immune responses and outcomes, sex and age are often ignored in vaccine research. Herein, we review the known sex differences in the immunogenicity, effectiveness, reactogenicity, and non-specific effects of vaccination over the lifespan. Ways in which these data can be leveraged to improve vaccine research are described.

Association of Frailty, Age, and Biological Sex With Severe Acute Respiratory Syndrome Coronavirus 2 Messenger RNA Vaccine-Induced Immunity in Older Adults

BACKGROUND

Male sex and old age are risk factors for severe coronavirus disease 2019, but the intersection of sex and aging on antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines has not been characterized.

METHODS

Plasma samples were collected from older adults (aged 75-98 years) before and after 3 doses of SARS-CoV-2 mRNA vaccination, and from younger adults (aged 18-74 years) post-dose 2, for comparison. Antibody binding to SARS-CoV-2 antigens (spike protein [S], S receptor-binding domain, and nucleocapsid), functional activity against S, and live-virus neutralization were measured against the vaccine virus and the Alpha, Delta, and Omicron variants of concern (VOCs).

RESULTS

Vaccination induced greater antibody titers in older females than in older males, with both age and frailty associated with reduced antibody responses in males but not females. Responses declined significantly in the 6 months after the second dose. The third dose restored functional antibody responses and eliminated disparities caused by sex, age, and frailty in older adults. Responses to the VOCs, particularly the Omicron variant, were significantly reduced relative to the vaccine virus, with older males having lower titers to the VOCs than older females. Older adults had lower responses to the vaccine and VOC viruses than younger adults, with greater disparities in males than in females.

CONCLUSIONS

Older and frail males may be more vulnerable to breakthrough infections owing to low antibody responses before receipt of a third vaccine dose. Promoting third dose coverage in older adults, especially males, is crucial to protecting this vulnerable population.