SARS-CoV-2 vaccination induces mucosal antibody responses in previously infected individuals

Mucosal immune responses to SARS-CoV-2 infection and COVID-19 vaccination

SARS-CoV-2 continues to circulate in the community. We hypothesise that mucosal immunity is required to prevent continuing viral acquisition and transmission.

OBJECTIVES

To determine whether SARS-CoV-2 infection or vaccination elicits specific neutralising antibodies in saliva, and to assess the longevity of protection.

METHODS

Initially, 111 COVID-19 convalescent participants were recruited, 11-369 days after diagnosis. Saliva and blood samples were assayed for antibodies specific for Spike protein, Receptor Binding Domain and Nucleoprotein. In a second cohort, 123 participants were recruited. Saliva and serum antibodies to the same antigens were assayed before and after their first and second COVID-19 vaccinations, with 150 day follow up.

RESULTS

Natural infection induces and boosts IgA and IgG in oral fluid and serum; vaccination does not induce or boost specific saliva IgA; IgG can be found in saliva after vaccination, but only when serum IgG concentrations are high; IgA is important for SARS-CoV-2 neutralisation activity by oral fluid, but there can also be contributions from serum IgG and other factors.

CONCLUSIONS

New COVID-19 vaccines should target both systemic and mucosal immunity, to establish a first line of immune defence at the mucosal barrier. This would benefit vulnerable patient populations and may help to eradicate SARS-CoV-2 circulation.

Hybrid B- and T-Cell Immunity Associates With Protection Against Breakthrough Infection After Severe Acute Respiratory Syndrome Coronavirus 2 Vaccination in Avon Longitudinal Study of Parents and Children (ALSPAC) Participants

BACKGROUND

Immunological memory to vaccination and viral infection involves the coordinated action of B and T cells; thus, integrated analysis of these 2 components is critical for understanding their respective contributions to protection against breakthrough infections (BIs) after vaccination.

METHODS

We investigated cellular and humoral immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and/or vaccination in 300 adult participants from the Avon Longitudinal Study of Parents and Children (ALSPAC). Participants were grouped by those with (cases) and without (controls) a history of SARS-CoV-2 infection. To provide a quantitative correlate for protection against BI in the 8-month period after the study, Youden index thresholds were calculated for all immune measures analyzed.

RESULTS

The magnitude of antibody and T-cell responses following the second vaccine dose was associated with protection against BI in participants with a history of SARS-CoV-2 infection (cases), but not in infection-naive controls. Over 8 months of follow-up, 2 threshold combinations provided the best performance for protection against BI in cases: (i) anti-spike immunoglobulin G (IgG) (≥666.4 binding antibody units [BAU]/mL) combined with anti-nucleocapsid pan-immunoglobulin (pan-Ig) (≥0.1332 BAU/mL) and (ii) spike 1-specific T cells (≥195.6 spot-forming units/106 peripheral blood mononuclear cells) combined with anti-N pan-Ig (≥0.1332 BAU/mL). Both combinations offered 100% specificity for detecting cases without BI, with sensitivities of 83.3% and 72.2%, respectively.

CONCLUSIONS

Collectively, these results suggest that hybrid B- and T-cell immunity offers superior protection from BI after coronavirus disease 2019 (COVID-19) vaccination, and this finding has implications for designing next-generation COVID-19 vaccines that are capable of eliciting immunity to a broader repertoire of SARS-CoV-2 proteins.

An intranasal subunit vaccine induces protective systemic and mucosal antibody immunity against respiratory viruses in mouse models

Although vaccines are usually given intramuscularly, the intranasal delivery route may lead to better mucosal protection and limit the spread of respiratory virus while easing administration and improving vaccine acceptance. The challenge, however, is to achieve delivery across the selective epithelial cell barrier. Here we report on a subunit vaccine platform, in which the antigen is genetically fused to albumin to facilitate FcRn-mediated transport across the mucosal barrier in the presence of adjuvant. Intranasal delivery in conventional and transgenic mouse models induces both systemic and mucosal antigen-specific antibody responses that protect against challenge with SARS-CoV-2 or influenza A. When benchmarked against an intramuscularly administered mRNA vaccine or an intranasally administered antigen fused to an alternative carrier of similar size, only the albumin-based intranasal vaccine yields robust mucosal IgA antibody responses. Our results thus suggest that this needle-free, albumin-based vaccine platform may be suited for vaccination against respiratory pathogens.

Mucosal and Systemic Antibody Responses After Boosting With a Bivalent Messenger RNA Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine

BACKGROUND

Mucosal immunity plays a critical role in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and replication. Understanding the capacity of coronavirus disease 2019 (COVID-19) vaccines to elicit both mucosal and systemic antibodies could help optimize vaccination strategies.

METHODS

We conducted an open-label, phase 1/2 adaptive-design clinical trial to evaluate the safety and immunogenicity of COVID-19 immunizations. Healthy adults received 2 priming doses of mRNA-1273, a booster dose of mRNA-1273, and a second booster of bivalent (WA-1 and BA.4/BA.5) mRNA-1273.222. Adverse event data were collected. Serum and mucosal immunity were evaluated.

RESULTS

One hundred six persons were enrolled. Thirty received all 4 study-related vaccine doses. All vaccines were well tolerated, with injection site pain, malaise, myalgias, and headache being the most frequently reported symptoms. Among those who received a second booster, 24 of 30 (80%) had serological evidence of SARS-CoV-2 infection. Following the second booster, increases in geometric mean binding and pseudovirus neutralization antibody titers to the ancestral strain and BA.1 and BA.5 variants were observed. Increases in mucosal immunoglobulin G and immunoglobulin A (IgA) antibodies in nasal and salivary samples were observed in both previously infected and infection-naive participants, although prior infection markedly boosted virus-specific mucosal IgA responses.

CONCLUSIONS

The mRNA-1273.222 booster vaccine was safe and immunogenic and induced mucosal antibody responses in previously infected and infection-naive persons.

CLINICAL TRIALS REGISTRATION

NCT04889209.

Beyond the Pandemic Era: Recent Advances and Efficacy of SARS-CoV-2 Vaccines Against Emerging Variants of Concern

Vaccination has been instrumental in curbing the transmission of SARS-CoV-2 and mitigating the severity of clinical manifestations associated with COVID-19. Numerous COVID-19 vaccines have been developed to this effect, including BioNTech-Pfizer and Moderna's mRNA vaccines, as well as adenovirus vector-based vaccines such as Oxford-AstraZeneca. However, the emergence of new variants and subvariants of SARS-CoV-2, characterized by enhanced transmissibility and immune evasion, poses significant challenges to the efficacy of current vaccination strategies. In this review, we aim to comprehensively outline the landscape of emerging SARS-CoV-2 variants of concern (VOCs) and sub-lineages that have recently surfaced in the post-pandemic years. We assess the effectiveness of existing vaccines, including their booster doses, against these emerging variants and subvariants, such as BA.2-derived sub-lineages, XBB sub-lineages, and BA.2.86 (Pirola). Furthermore, we discuss the latest advancements in vaccine technology, including multivalent and pan-coronavirus approaches, along with the development of several next-generation coronavirus vaccines, such as exosome-based, virus-like particle (VLP), mucosal, and nanomaterial-based vaccines. Finally, we highlight the key challenges and critical areas for future research to address the evolving threat of SARS-CoV-2 subvariants and to develop strategies for combating the emergence of new viral threats, thereby improving preparedness for future pandemics.

A parainfluenza virus 5 (PIV5)-vectored intranasal SARS-CoV-2 vaccine (CVXGA1) elicits protective and long-lasting immunity in nonhuman primates

Waning immunity from approved COVID-19 vaccines and emerging variants of SARS-CoV-2 necessitate the need to develop alternative COVID-19 vaccines for improved durability and broader protection. This work investigates the efficacy and mucosal, humoral, and cellular immunogenicity of intranasal, parainfluenza virus 5 (PIV5)-vectored COVID-19 vaccine CVXGA1 in an African green monkey (AGM) nonhuman primate model. A single intranasal dose of CVXGA1 induced robust and sustained humoral and cellular immune responses in AGMs and protected against SARS-CoV-2 ancestral WA1 strain and alpha variant challenge infection in the respiratory tracts as demonstrated by lack of viral load and greatly decreased histopathology. Mucosal IgA antibodies were detected in the upper and lower respiratory tracts of immunized AGMs. CVXGA1-vaccinated AGMs maintained serum anti-S IgG and IgA antibody titers for over 245 days. S-specific CD4+ and CD8+ T cells producing predominantly IFN-γ, TNF-α, MIP-β, and CD107α cytokines peaked on day 28 and could be detected on day 180 by intracellular cytokine staining of peripheral blood mononuclear cells (PBMC). IL13-secreting CD4+ and CD8+ T cells were minimally detected, indicative of a dominant type 1 immune response. These data supported the clinical evaluation of CVXGA1 intranasal COVID-19 vaccine. These data demonstrate that intranasal immunization with CVXGA1 induces long-lasting protective SARS-CoV-2 S-specific mucosal, humoral, and cellular responses in AGMs.IMPORTANCEThe continued threat of SARS-CoV-2 indicates the need for a novel vaccine that induces long-lasting mucosal, cellular, and humoral immunity, as well as block transmission. This work demonstrates that intranasal, PIV5 viral-vectored SARS-CoV-2 vaccine CVXGA1 induces mucosal immunity and long-lasting cellular and humoral immunity that protects African green monkeys from SARS-CoV-2 challenge. The ability of our intranasal vaccine to elicit long-lasting mucosal, cellular, and humoral immunity against SARS-CoV-2 indicates great promise of the PIV5-vectored COVID-19 vaccine for further clinical development.

Group IIC self-splicing intron-derived novel circular RNA vaccine elicits superior immune response against RSV

Introduction

The remarkable commercial success of mRNA vaccines against COVID-19 and tumors, along with their potential as therapeutic drugs, has significantly boosted enthusiasm for circular RNAs (circRNA) as a promising next-generation therapeutic platform. The development of novel circRNA cyclization technologies represents a significant leap forward in RNA engineering and therapeutic applications. Recent advancements in group I and IIB self-splicing intron-based ribozymes have enabled precise cyclization of RNA molecules. However, this approach faces significant limitations, including low cyclization efficiency and the requirement for additional additives, which restrict its broader application. Group IIC self-splicing introns represent the shortest known selfsplicing ribozymes and employ a splicing mechanism that is fundamentally distinct from that of group IIB self-splicing introns. However, the potential of group IIC self-splicing introns to carry exogenous sequences for the development of circular RNA-based platforms remains an open question and warrants further investigation.

Methods

Here, we demonstrate that group IIC self-splicing introns can efficiently circularize and express exogenous proteins of varying lengths, as evidenced by luciferase and GFP reporter systems. Leveraging structural biology-based design, we engineered the RSV pre-F protein and validated the potential of IIC self-splicing introns as a vaccine platform for preventing infectious diseases.

Results

In mouse models, the novel nucleic acid vaccine developed using IIC self-splicing introns elicited superior immunogenicity and in vivo protective efficacy compared to protein-adjuvant vaccines.

Discussion

The development of the novel circular RNA vaccine platform holds significant promise for advancing next-generation therapeutics for disease treatment and prevention.

Viral infection and antiviral immunity in the oral cavity

Individual tissues have distinct antiviral properties garnered through various mechanisms, including physical characteristics, tissue-resident immune cells and commensal organisms. Although the oral mucosa has long been appreciated as a critical barrier tissue that is exposed to a continuous barrage of pathogens, many fundamental aspects of the antiviral immune response in this tissue remain unknown. Several viral pathogens, such as herpesviruses and human papillomaviruses, have been acknowledged both historically and at present for infections in the oral cavity that result in substantial clinical burden. However, recent viral outbreaks, including those with SARS-CoV-2 and mpox, featured oral symptoms even though these viruses are not generally considered oral pathogens. Ensuing studies have shown that the oral cavity is an important locale for viral infection and potential transmission of newly emergent or re-emergent pathogens, highlighting the need for an increased understanding of the mechanisms of antiviral immunity at this site. In this Review, we provide a broad overview of antiviral immune responses in the oral cavity and discuss common viral infections and their manifestations in the oral mucosa. In addition, we present current mouse models for the study of oral viral infections.

Estimating the effect of COVID-19 vaccination and prior infection on cycle threshold values as a proxy of SARS-CoV-2 viral load

OBJECTIVES

SARS-CoV-2 viral load could be an important parameter for transmission potential. Here, we use quantitative reverse transcription-polymerase chain reaction cycle threshold (Ct) values as a proxy for viral load. We assess the effect of COVID-19 vaccination and prior infection status on Ct value while accounting for the virus variant.

METHODS

Using Dutch SARS-CoV-2 community testing data (n = 409,925 samples) from 8 March 2021 to 31 December 2022, separate univariable linear regressions were conducted for each explanatory variable, including age, sex, testing date, variant of infection, time since symptom onset, and testing laboratory. Subsequently, causal inference analysis assessed the impact of prior infection and vaccination status on Ct values, employing inverse propensity score weighting to adjust for confounders.

RESULTS

Our findings revealed a negative correlation between age and Ct values. Additionally, we observed modest differences in Ct values between different variants of infection, with lower Ct values (indicative of higher viral load) noted for Omicron variants compared to earlier variants. In addition, our results indicated an increase in Ct value (lower viral load) with prior infection. Conversely, the impact of vaccination was less pronounced.

CONCLUSIONS

We observed an association between prior infection status and higher Ct values, suggesting a decrease in viral load, which could possibly indicate lower transmissibility.

A live attenuated SARS-CoV-2 vaccine constructed by dual inactivation of NSP16 and ORF3a

BACKGROUND

Live attenuated vaccines against SARS-CoV-2 activate all phases of host immunity resembling a natural infection and they block viral transmission more efficiently than existing vaccines in human use. In our prior work, we characterised an attenuated SARS-CoV-2 variant, designated d16, which harbours a D130A mutation in the NSP16 protein, inactivating its 2'-O-methyltransferase function. The d16 variant has demonstrated an ability to induce both mucosal and sterilising immunity in animal models. However, further investigation is required to identify any additional modifications to d16 that could mitigate concerns regarding potential virulence reversion and the suboptimal regulation of the proinflammatory response.

METHODS

Mutations were introduced into molecular clone of SARS-CoV-2 and live attenuated virus was recovered from cultured cells. Virological, biochemical and immunological assays were performed in vitro and in two animal models to access the protective efficacies of the candidate vaccine strain.

FINDINGS

Here we describe evaluation of a derivative of d16. We further modified the d16 variant by inverting the open reading frame of the ORF3a accessory protein, resulting in the d16i3a strain. This modification is anticipated to enhance safety and reduce pathogenicity. d16i3a appeared to be further attenuated in hamsters and transgenic mice compared to d16. Intranasal vaccination with d16i3a stimulated humoural, cell-mediated and mucosal immune responses, conferring sterilising protection against SARS-CoV-2 Delta and Omicron variants in animals. A version of d16i3a expressing the XBB.1.16 spike protein further expanded the vaccine's protection spectrum against circulating variants. Notably, this version has demonstrated efficacy as a booster in hamsters, providing protection against Omicron subvariants and achieving inhibition of viral transmission.

INTERPRETATION

Our work established a platform for generating safe and effective live attenuated vaccines by dual inactivation of NSP16 and ORF3a of SARS-CoV-2.

FUNDING

This work was supported by National Key Research and Development Program of China (2021YFC0866100, 2023YFC3041600, and 2023YFE0203400), Hong Kong Health and Medical Research Fund (COVID190114, CID-HKU1-9, and 23220712), Hong Kong Research Grants Council (C7142-20GF and T11-709/21-N), Hong Kong Innovation and Technology Commission grant (MHP/128/22), Guangzhou Laboratory (EKPG22-01) and Health@InnoHK (CVVT). Funding sources had no role in the writing of the manuscript or the decision to submit it for publication.

Systemic and Mucosal Antibody Responses to SARS-CoV-2 Variant-Specific Prime-and-Boost and Prime-and-Spike Vaccination: A Comparison of Intramuscular and Intranasal Bivalent Vaccine Administration in a Murine Model

Background: The rapid genetic evolution of SARS-CoV-2 has led to the emergence of immune-evading, highly transmissible variants of concern (VOCs). This prompts the need for next-generation vaccines that elicit robust mucosal immunity in the airways to directly curb viral infection. Objective: Here, we investigate the impact of heterologous variant prime-boost regimens on humoral responses, focusing on intramuscular (IM) and intranasal (IN) routes of administration. Using a murine model, we assessed the immunogenicity of unadjuvanted protein boosts with Wu-1, Omicron BA.4/5, or Wu-1 + BA.4/5 spike antigens following monovalent or bivalent IM priming with mRNA-LNP vaccines. Results: IM priming induced strong systemic total and neutralizing antibody responses that were further enhanced by IN boosts with BA.4/5. IN boosting achieved the broadest serum neutralization across all VOCs tested. Notably, bivalent mRNA-LNP IM priming induced robust, cross-variant serum neutralizing antibody production, independent of subsequent IN boost combinations. Conclusions: Our findings highlight the benefit of including distinct antigenic variants in the prime vaccination followed by a variant-tailored IN boost to elicit both systemic and mucosal variant-specific responses that are potentially capable of reducing SARS-CoV-2 transmission.

Evaluation of dual pathogen recognition receptor agonists as adjuvants for respiratory syncytial virus - virus-like particles for pulmonary delivery

Introduction

Respiratory syncytial virus (RSV) remains a significant global health concern, particularly for infants and young children in developing countries. Despite ongoing research efforts, an effective RSV vaccine has yet to be approved for widespread use. Use of two separate pattern recognition receptor (PRR) agonists as adjuvants in vaccine formulations has shown to enhance the immune response against the antigen. The limitation with the use of two adjuvants is that they need not necessarily bind to PRRs on the same cell. This study evaluates the efficacy of two different dual PRR binding chimeric molecules CL413 (TLR2/TLR7 agonist) and CL429 (TLR2/NOD2 agonist) as adjuvants for RSV virus-like particles (VLPs) delivered via the pulmonary route in mice for induction of mucosal and systemic immunity.

Methods

BALB/c mice were immunized twice with the RSV-VLPs alone or adjuvanted with CL413, CL429, mixture of single PRR agonists Pam3CSK4+ L18-MDP or Pam3CSK4+ imiquimod via the pulmonary route. The mixture of single PRR agonists adjuvants was used as control for chimeric adjuvants. Immune responses were evaluated by measuring antibody levels in sera and respiratory tract; cytokine production, B and T cell responses in the lungs and spleen.

Results

Pulmonary immunization with CL413-adjuvanted VLPs induced robust nasal IgA responses against the RSV F and G proteins, which was not observed for the other adjuvant combinations. CL413 also enhanced serum IgG levels and promoted a balanced Th1/Th2 response, as evidenced by IgG2a/IgG1 ratios. CL413 elicited strong pro-inflammatory responses in the lungs of mice, including elevated levels of IFN-γ, TNF-α, IL-6, and IL-17A. Flow cytometry analysis revealed increased numbers of tissue-resident class-switched B cells in the lungs of mice that were immunized with VLPs adjuvanted with CL413 and CL429. CD4+ and CD8+ T cell responses were also enhanced in both lungs and spleens of mice receiving VLPs adjuvanted with chimeric molecules to various extents. Mice immunized with formalin inactivated RSV (FI-RSV), which are used as the positive control for vaccine induced pathology after RSV challenge developed alveolitis, perivascular infiltration. While all the mice receiving adjuvanted VLP formulations showed protection against lung pathology after RSV challenge.

Discussion

The lack of pathology, combined with the robust mucosal and systemic immune responses, suggests that pulmonary delivery of adjuvanted RSV-VLPs may provide effective protection without the risk of vaccine-enhanced disease. The study also demonstrates that the chimeric TLR2/TLR7 agonist CL413 is a promising adjuvant for RSV-VLPs to induce mucosal and systemic immune response and warrant further investigations in more advanced preclinical models.

Protection conferred by mucosal novel bivalent Klebsiella pneumoniae vaccine immunization associates with presence of lung CD4+ TRM

Klebsiella pneumoniae is the principal cause of hospital-acquired infection with a high morbidity and mortality in immunocompromised individuals, yet no vaccine is approved. Here, we developed a novel bivalent subunit vaccine for the prevention of K. pneumoniae infection based on the outer membrane protein GlnH and the fimbriae protein FimA. The survival rate of immunized mice was significantly increased compared to that of unimmunized mice, while the bacterial burden, weight loss, and lung pathology were drastically reduced. Furthermore, vaccine-elicited CD4+ TRM cells were observed in lung tissues and appeared to play a critical role in vaccine efficacy. Transcriptomic analysis of total lung tissues from mice treated by FTY720 (S1PR1 inhibitor that blocks lymphocyte egress from secondary lymphoid structures) showed that cell activation, cytokine secretion and enhancement of the killing ability of neutrophils were related to the mechanism of protection against K. pneumoniae infection. These findings indicate that GlnH and FimA are effective candidate bivalent vaccine to fight K. pneumoniae infection.

IgA class switching enhances neutralizing potency against SARS-CoV-2 by increased antibody hinge flexibility

IgA antibodies are critical components of the mucosal immune barrier, providing essential first-line defense against viral infections. In this study, we investigated the impact of antibody class switching on neutralization efficacy by engineering recombinant antibodies of different isotypes (IgA1, IgG1) with identical variable regions from SARS-CoV-2 convalescent patients. A potent, broad-spectrum neutralizing monoclonal antibody CAV-C65 exhibited a ten-fold increase in neutralization potency upon switching from IgG1 to IgA1 monomer. Structural analysis revealed that this antibody binds to two adjacent receptor binding domains on the spike protein. Enhanced neutralization by IgA1 was attributed to the combined effects of increased affinity, unique hinge region properties, and potential cross-linking of viral particles. Inhaled CAV-C65 IgA1 demonstrated prophylactic efficacy against lethal SARS-CoV-2 infection in hACE2 mice. These findings highlight the pivotal role of IgA in antiviral immunity and inform the development of IgA-based therapeutics.

A single immunization with intranasal Newcastle disease virus (NDV)-based XBB.1.5 variant vaccine reduces disease and transmission in animals against matched-variant challenge

The rapid development of coronavirus disease 2019 (COVID-19) vaccines has helped mitigate the initial impact of the pandemic. However, in order to reduce transmission rates and protect more vulnerable and immunocompromised individuals unable to mount an effective immune response, development of a next-generation of mucosal vaccines is necessary. Here, we developed an intranasal Newcastle disease virus (NDV)-based vaccine expressing the spike of the XBB.1.5 variant stabilized in its pre-fusion conformation (NDV-HXP-S). We demonstrated that one or two intranasal immunizations with live NDV-HXP-S expressing the XBB.1.5 spike induces systemic and mucosal antibody responses in mice and protects them from a challenge with the XBB.1.5 variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Furthermore, one or two intranasal vaccinations with NDV-HXP-S XBB.1.5 protected hamsters from variant matched infection and reduced virus emission, thereby providing complete protection to naïve animals in a direct contact transmission study. The data shown in this study supports the notion that intranasal vaccination with variant-adapted NDV-HXP-S induces protective mucosal immunity and reduces transmission rates, highlighting the robust protective efficacy of a single mucosal vaccination in mice and hamsters.

Mucosal immune response in biology, disease prevention and treatment

The mucosal immune system, as the most extensive peripheral immune network, serves as the frontline defense against a myriad of microbial and dietary antigens. It is crucial in preventing pathogen invasion and establishing immune tolerance. A comprehensive understanding of mucosal immunity is essential for developing treatments that can effectively target diseases at their entry points, thereby minimizing the overall impact on the body. Despite its importance, our knowledge of mucosal immunity remains incomplete, necessitating further research. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has underscored the critical role of mucosal immunity in disease prevention and treatment. This systematic review focuses on the dynamic interactions between mucosa-associated lymphoid structures and related diseases. We delve into the basic structures and functions of these lymphoid tissues during disease processes and explore the intricate regulatory networks and mechanisms involved. Additionally, we summarize novel therapies and clinical research advances in the prevention of mucosal immunity-related diseases. The review also addresses the challenges in developing mucosal vaccines, which aim to induce specific immune responses while maintaining tolerance to non-pathogenic microbes. Innovative therapies, such as nanoparticle vaccines and inhalable antibodies, show promise in enhancing mucosal immunity and offer potential for improved disease prevention and treatment.

Mucosal SARS-CoV-2 S1 adenovirus-based vaccine elicits robust systemic and mucosal immunity and protects against disease in animals

The COVID-19 pandemic has emphasized the importance and need for accessible safe, effective, and versatile vaccine platforms. While approved SARS-CoV-2 vaccines have been instrumental in saving lives and reducing healthcare and economic burdens, the induction of mucosal immunity remains an unmet need. Here, we engineered and evaluated a non-replicating adenovirus 5 (rAd5)-based vaccine expressing the SARS-CoV-2 S1 subunit (rAd5-SARS2-S1). We assessed the immunogenicity, durability, and protective efficacy of intramuscular (IM) and intranasal (IN) administration of rAd5-SARS2-S1 in mice and Syrian hamsters. Two IM or IN doses of rAd5-SARS2-S1 elicited robust and sustained Th1-skewed S1-specific serum IgG, neutralizing antibodies (nAbs) against several SARS-CoV-2 variants and systemic antigen-specific memory T cell responses in mice. Additionally, IN vaccination induced potent and long-lasting mucosal S1-specific IgG, IgA, and nAbs and pulmonary memory T cells. Importantly, while IM vaccine significantly ameliorated disease severity in hamsters by reducing viral burden, lung pathology, and, to some extent, weight loss, IN immunization significantly reduced viral replication and provided superior protection against disease and weight loss. Together, our study demonstrates that the rAd5-SARS2-S1 vaccine is immunogenic in both mice and hamsters when administered intramuscularly or intranasally, with IN administration providing better protection. These findings suggest that IN delivery of rAd5-SARS2-S1 could be a promising approach for inducing mucosal and systemic immunity, offering enhanced protection against SARS-CoV-2 and emerging variants.

IMPORTANCE

This publication presents an assessment of the immune response and effectiveness of a vaccine containing genetically modified non-replicating recombinant that expresses the S1 subunit protein of SARS-CoV-2. We conducted a comparative analysis of the immune response potency, durability, and protective effectiveness of this vaccine using intramuscular (IM) and intranasal (IN) inoculation in mice and Syrian hamsters. Our findings indicate that both vaccinations were effective in stimulating strong and long-lasting immune responses, both locally and across the body, when administered through either IM or IN methods. Crucially, our study demonstrated that the IN vaccination outperformed the IM vaccine by effectively and significantly suppressing the multiplication of the virus in the lungs and nasal turbinates. Additionally, the IN vaccine provided protection against disease-related weight loss and lung damage in the animals. This work showcases the potential of intranasal administration as a viable method to stimulate both mucosal and systemic immunity. This technique provides improved defense against SARS-CoV-2 and maybe additional variations.

Comprehensive analyses of immune activity in COVID-19-vaccinated idiopathic pulmonary fibrosis patients

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease, characterized by impaired wound repair, tissue remodeling and fibrosis. Immune system may participate in the development and progression of the disease as indicated by altered activity in IPF sufferers. This study investigates the immune response to the BNT162b2 COVID-19 vaccine in patients with IPF compared to healthy controls, with a particular focus on evaluation of antibody responses, interferon-gamma release, cytokine profiling and a broad panel of immune cell subpopulations. IPF patients without prior exposure to SARS-CoV-2 had undetectable levels of anti-N IgG antibodies, highlighting their lack of previous infection. After vaccination, IPF patients showed a significant increase in anti-S1 IgG and IgA antibodies, though their levels were lower compared to healthy controls and convalescent IPF patients. Additionally, IPF patients exhibited altered proportions of regulatory T cells (Tregs) and effector T lymphocytes (Teffs) before and after vaccination. Specifically, IPF patients had higher percentages of Tregs with a Th2 phenotype and Th17 Tregs, along with reduced proportions of Th1/17 Tregs. Teffs in IPF patients showed a decrease in Th1-like and Th2-like populations after vaccination. Moreover, IPF patients demonstrated elevated populations of cytotoxic T lymphocytes (Tc) before vaccination and increased levels of γδ Tc cells throughout the study. Alterations in cytokine profiles were also observed, IPF patients showed higher levels of IL-6 and IL-22 compared to healthy controls. These findings suggest a distinct immune response in IPF patients to the COVID-19 vaccine, characterized by differences in antibody production, T cell differentiation and cytokine secretion compared to healthy individuals.

COVID-19 mRNA Vaccines Induce Robust Levels of IgG but Limited Amounts of IgA Within the Oronasopharynx of Young Children

BACKGROUND

Understanding antibody responses to SARS-CoV-2 vaccination is crucial for refining COVID-19 immunization strategies. Generation of mucosal immune responses, including mucosal IgA, could be of potential benefit to vaccine efficacy; however, limited evidence exists regarding the production of mucosal antibodies following the administration of current mRNA vaccines to young children.

METHODS

We measured the levels of antibodies against SARS-CoV-2 from a cohort of children under 5 years of age (n = 24) undergoing SARS-CoV-2 mRNA vaccination (serially collected, matched serum and saliva samples) or in a convenience sample of children under 5 years of age presenting to pediatric emergency department (nasal swabs, n = 103). Furthermore, we assessed salivary and nasal samples for the ability to induce SARS-CoV-2 spike-mediated neutrophil extracellular traps (NET) formation.

RESULTS

Longitudinal analysis of post-vaccine responses in saliva revealed the induction of SARS-CoV-2-specific IgG but not IgA. Similarly, SARS-CoV-2-specific IgA was only observed in nasal samples obtained from previously infected children with or without vaccination, but not in vaccinated children without a history of infection. In addition, oronasopharyngeal samples obtained from children with prior infection were able to trigger enhanced spike-mediated NET formation, and IgA played a key role in driving this process.

CONCLUSIONS

Despite the induction of specific IgG in the oronasal mucosa, current intramuscular vaccines have limited ability to generate mucosal IgA in young children. These results confirm the independence of mucosal IgA responses from systemic humoral responses following mRNA vaccination and suggest potential future vaccination strategies for enhancing mucosal protection in this young age group.

mRNA vaccine-induced IgG mediates nasal SARS-CoV-2 clearance in mice

Coronavirus disease 2019 (COVID-19) mRNA vaccines that have contributed to controlling the SARS-CoV-2 pandemic induce specific serum antibodies, which correlate with protection. However, the neutralizing capacity of antibodies for emerging SARS-CoV-2 variants is altered. Suboptimal antibody responses are observed in patients with humoral immunodeficiency diseases, ongoing B cell depletion therapy, and aging. Common experimental mouse models with altered B cell compartments, such as B cell depletion or deficiency, do not fully recapitulate scenarios of declining or suboptimal antibody levels as observed in humans. We report on SARS-CoV-2 immunity in a transgenic mouse model with restricted virus-specific antibodies. Vaccination of C57BL/6-Tg(IghelMD4)4Ccg/J mice with unmodified or N1mΨ-modified mRNA encoding for ancestral spike (S) protein and subsequent challenge with mouse-adapted SARS-CoV-2 provided insights into antibody-independent immunity and the impact of antibody titers on mucosal immunity. Protection against fatal disease was independent of seroconversion following mRNA vaccination, suggesting that virus-specific T cells can compensate for suboptimal antibody levels. In contrast, mRNA-induced IgG in the nasal conchae limited the local viral load and disease progression. Our results indicate that parenteral mRNA immunization can elicit nasal IgG antibodies that effectively suppress local viral replication, highlighting the potential of vaccines in controlling SARS-CoV-2 transmission and epidemiology.

Safety and immunogenicity of heterologous boosting with orally administered aerosolized bivalent adenovirus type-5 vectored COVID-19 vaccine and B.1.1.529 variant adenovirus type-5 vectored COVID-19 vaccine in adults 18 years and older: a randomized, double blinded, parallel controlled trial

Vaccination strategies that can induce a broad spectrum immune response are important to enhance protection against SARS-CoV-2 variants. We conducted a randomized, double-blind and parallel controlled trial to evaluate the safety and immunogenicity of the bivalent (5×1010viral particles) and B.1.1.529 variant (5×1010viral particles) adenovirus type-5 (Ad5) vectored COVID-19 vaccines administrated via inhalation. 451 eligible subjects aged 18 years and older who had been vaccinated with three doses inactivated COVID-19 vaccines were randomly assigned to inhale one dose of either B.1.1.529 variant Ad5 vectored COVID-19 vaccine (Ad5-nCoVO-IH group, N=150), bivalent Ad5 vectored COVID-19 vaccine (Ad5-nCoV/O-IH group, N=151), or Ad5 vectored COVID-19 vaccine (5×1010viral particles; Ad5-nCoV-IH group, N=150). Adverse reactions reported by 37 (24.67%) participants in the Ad5-nCoVO-IH group, 28 (18.54%) in the Ad5-nCoV/O-IH group, and 26 (17.33%) in the Ad5-nCoV-IH group with mainly mild to moderate dry mouth, oropharyngeal pain, headache, myalgia, cough, fever and fatigue. No serious adverse events related to the vaccine were reported. Investigational vaccines were immunogenic, with significant difference in the GMTs of neutralizing antibodies against Omicron BA.1 between Ad5-nCoV/O-IH (43.70) and Ad5-nCoV-IH (29.25) at 28 days after vaccination (P=0.0238). The seroconversion rates of neutralizing antibodies against BA.1 in Ad5-nCoVO-IH, Ad5-nCoV/O-IH, and Ad5-nCoV-IH groups were 56.00%, 59.60% and 48.67% with no significant difference among the groups. Overall, the investigational vaccines were demonstrated to be safe and well tolerated in adults, and was highly effective in inducing mucosal immunities in addition to humoral and cellular immune responses defending against SARS-CoV-2 variants.Trial registration: Chictr.org identifier: ChiCTR2200063996.

Salivary Immunoglobulin a Alterations in Health and Disease: A Bibliometric Analysis of Diagnostic Trends from 2009 to 2024

BACKGROUND/OBJECTIVES

Salivary immunoglobulin A (IgA) is a mediator of local immunity and host defence. Altered IgA levels may predispose to bacterial invasion of the mucosa in the gastrointestinal tract, including the oral cavity. Our study aimed to present the diagnostic trends related to salivary IgA in health and disease based on a bibliometric analysis of published papers between 2009 and 2024.

METHODS

By 14 September 2024, 1247 English original articles were found in the database Web of Science. We selected 838 records considering the diagnostic usefulness of IgA in human subjects. Based on bibliographic data, we created citation and keyword co-occurrence maps using VOSviewer 1.6.20.

RESULTS

Most articles belonged to the "Sport Sciences" category (n = 169), followed by the "Immunology" category (n = 93). The Brazilian researcher Alexandre Moreira from the University of Sao Paulo had the most published and most frequently cited papers. Most of the included articles came from the USA (n = 158), England (n = 105), Brazil (n = 95), and Japan (n = 95). The most cited article described research on IgA in response to SARS-CoV-2 infection (n = 690), but the subsequent two papers considered the role of salivary IgA in the dysbiosis of the intestinal microbiota in inflammatory bowel diseases (n = 272) and the formation of systemic immune responses from the gastrointestinal tract (n = 245).

CONCLUSIONS

Salivary IgA is a widely evaluated diagnostic marker in both patients and healthy individuals. Numerous reports have identified its changes as a result of physical exertion in various groups of athletes, during infections (including SARS-CoV-2) and in the course of local diseases (e.g., periodontal disease) or systemic diseases (e.g., inflammatory bowel disease).

A self-amplifying RNA RSV prefusion-F vaccine elicits potent immunity in pre-exposed and naïve non-human primates

Newly approved subunit and mRNA vaccines for respiratory syncytial virus (RSV) demonstrate effectiveness in preventing severe disease, with protection exceeding 80% primarily through the generation of antibodies. An alternative vaccine platform called self-amplifying RNA (saRNA) holds promise in eliciting humoral and cellular immune responses. We evaluate the immunogenicity of a lipid nanoparticle (LNP)-formulated saRNA vaccine called SMARRT.RSV.preF, encoding a stabilized form of the RSV fusion protein, in female mice and in non-human primates (NHPs) that are either RSV-naïve or previously infected. Intramuscular vaccination with SMARRT.RSV.preF vaccine induces RSV neutralizing antibodies and cellular responses in naïve mice and NHPs. Importantly, a single dose of the vaccine in RSV pre-exposed NHPs elicits a dose-dependent anamnestic humoral immune response comparable to a subunit RSV preF vaccine. Notably, SMARRT.RSV.preF immunization significantly increases polyfunctional RSV.F specific memory CD4+ and CD8+ T-cells compared to RSV.preF protein vaccine. Twenty-four hours post immunization with SMARRT.RSV.preF, there is a dose-dependent increase in the systemic levels of inflammatory and chemotactic cytokines associated with the type I interferon response in NHPs, which is not observed with the protein vaccine. We identify a cluster of analytes including IL-15, TNFα, CCL4, and CXCL10, whose levels are significantly correlated with each other after SMARRT.RSV.preF immunization. These findings suggest saRNA vaccines have the potential to be developed as a prophylactic RSV vaccine based on innate, cellular, and humoral immune profiles they elicit.

mRNA vaccines for infectious diseases - advances, challenges and opportunities

The concept of mRNA-based vaccines emerged more than three decades ago. Groundbreaking discoveries and technological advancements over the past 20 years have resolved the major roadblocks that initially delayed application of this new vaccine modality. The rapid development of nucleoside-modified COVID-19 mRNA vaccines demonstrated that this immunization platform is easy to develop, has an acceptable safety profile and can be produced at a large scale. The flexibility and ease of antigen design have enabled mRNA vaccines to enter development for a wide range of viruses as well as for various bacteria and parasites. However, gaps in our knowledge limit the development of next-generation mRNA vaccines with increased potency and safety. A deeper understanding of the mechanisms of action of mRNA vaccines, application of novel technologies enabling rational antigen design, and innovative vaccine delivery strategies and vaccination regimens will likely yield potent novel vaccines against a wide range of pathogens.

Repeated COVID-19 mRNA-based vaccination contributes to SARS-CoV-2 neutralizing antibody responses in the mucosa

To prevent infection by respiratory viruses and consequently limit virus circulation, vaccines need to promote mucosal immunity. The extent to which the currently used messenger RNA (mRNA)-based COVID-19 vaccines induce mucosal immunity remains poorly characterized. We evaluated mucosal neutralizing antibody responses in a cohort of 183 individuals. Participants were sampled at several time points after primary adenovirus vector-based or mRNA-based COVID-19 vaccination and after mRNA-based booster vaccinations. Our findings revealed that repeated vaccination with mRNA boosters promoted severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies in nasal secretions. Nasal and serum neutralizing antibody titers of both IgG and IgA isotypes correlated to one another. We investigated the source of these mucosal antibodies in a mouse model wherein mice received repeated mRNA vaccines for SARS-CoV-2. These experiments indicated that neutralizing antibody-producing cells reside in the spleen and bone marrow, whereas no proof of tissue homing to the respiratory mucosa was observed, despite the detection of mucosal antibodies. Serum transfer experiments confirmed that circulating antibodies were able to migrate to the respiratory mucosa. Collectively, these results demonstrate that, especially upon repeated vaccination, the currently used COVID-19 mRNA vaccines can elicit mucosal neutralizing antibodies and that vaccination might also stimulate mucosal immunity induced by previous SARS-CoV-2 infection. Moreover, migration of circulating antibodies to the respiratory mucosa might be a main mechanism. These findings advance our understanding of mRNA vaccine-induced immunity and have implications for the design of vaccine strategies to combat respiratory infections.

COVID-19 vaccines are effective at preventing symptomatic and severe infection among healthcare workers: A clinical review

Introduction

Health care workers (HCWs) have been at increased risk of infection during the SARS-CoV-2 pandemic and as essential workers have been prioritised for vaccination. Due to increased exposure HCW are considered a predictor of what might happen in the general population, particularly working age adults. This study aims to summarise effect of vaccination in this 'at risk' cohort.

Methods

Ovid MEDLINE and Embase were searched, and 358 individual articles were identified. Of these 49 met the inclusion criteria for review and 14 were included in a meta-analysis.

Results

Participants included were predominantly female and working age. Median time to infection was 51 days. Reported vaccine effectiveness against infection, symptomatic infection, and infection requiring hospitalisation were between 5 and 100 %, 34 and 100 %, and 65 and 100 % (respectively). No vaccinated HCW deaths were recorded in any study. Pooled estimates of protection against infection, symptomatic infection, and hospitalisation were, respectively, 84.7 % (95 % CI 72.6-91.5 %, p < 0.0001), 86.0 % (95 % CI 67.2 %-94.0 %; p < 0.0001), and 96.1 % (95 % CI 90.4 %-98.4 %). Waning protection against infection was reported by four studies, although protection against hospitalisation for severe infection persists for at least 6 months post vaccination.

Conclusions

Vaccination against SARS-CoV2 in HCWs is protective against infection, symptomatic infection, and hospitalisation. Waning protection is reported but this awaits more mature studies to understand durability more clearly. This study is limited by varying non-pharmacological responses to COVID-19 between included studies, a predominantly female and working age population, and limited information on asymptomatic transmission or long COVID protection.

Navigating the Landscape of B Cell Mediated Immunity and Antibody Monitoring in SARS-CoV-2 Vaccine Efficacy: Tools, Strategies and Clinical Trial Insights

Correlates of Protection (CoP) are biomarkers above a defined threshold that can replace clinical outcomes as primary endpoints, predicting vaccine effectiveness to support the approval of new vaccines or follow up studies. In the context of COVID-19 vaccination, CoPs can help address challenges such as demonstrating vaccine effectiveness in special populations, against emerging SARS-CoV-2 variants or determining the durability of vaccine-elicited immunity. While anti-spike IgG titres and viral neutralising capacity have been characterised as CoPs for COVID-19 vaccination, the contribution of other components of the humoral immune response to immediate and long-term protective immunity is less well characterised. This review examines the evidence supporting the use of CoPs in COVID-19 clinical vaccine trials, and how they can be used to define a protective threshold of immunity. It also highlights alternative humoral immune biomarkers, including Fc effector function, mucosal immunity, and the generation of long-lived plasma and memory B cells and discuss how these can be applied to clinical studies and the tools available to study them.

Preparation and immunological activity evaluation of an intranasal protein subunit vaccine against ancestral and mutant SARS-CoV-2 with curdlan sulfate/O-linked quaternized chitosan nanoparticles as carrier and adjuvant

Chitosan and its derivatives are ideal nasal vaccine adjuvant to deliver antigens to immune cells. Previously, we successfully used a chitosan derivative, O-(2-Hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (O-HTCC), and a β-glucan derivative, curdlan sulfate (CS), to prepare a nanoparticle adjuvant CS/O-HTCC which could deliver ovalbumin to antigen presenting cells (APCs) through nasal inhalation. In this article, we used SARS-CoV-2 spike receptor binding domain (S-RBD) as the antigen and CS/O-HTCC nanoparticles as the adjuvant to develop a nasal mucosal protein subunit vaccine, CS/S-RBD/O-HTCC. The humoral immunity, cell-mediated immunity and mucosal immunity induced by vaccines were evaluated. The results showed that CS/S-RBD/O-HTCC could induce desirable immunization with single or bivalent antigen through nasal inoculation, giving one booster vaccination with mutated S-RBD (beta) could bring about a broad cross reaction with ancestral and different mutated S-RBD, and vaccination of the BALB/c mice with CS/S-RBD/O-HTCC containing S-RBD mix antigens (ancestral and omicron) could induce the production of binding and neutralizing antibodies against both of the two antigens. Our results indicate that CS/O-HTCC is a promising nasal mucosal adjuvant to prepare protein subunit vaccine for both primary and booster immunization, and the adjuvant is suitable for loading more than one antigen for preparing multivalent vaccines.

Neutralizing and binding antibody responses to SARS-CoV-2 with hybrid immunity in pregnancy

Hybrid immunity against SARS-CoV-2 has not been well studied in pregnancy. We conducted a comprehensive analysis of neutralizing antibodies (nAb) and binding antibodies in pregnant individuals who received mRNA vaccination, natural infection, or both. A third vaccine dose augmented nAb levels compared to the two-dose regimen or natural infection alone; this effect was more pronounced in hybrid immunity. There was reduced anti-Omicron nAb, but the maternal-fetal transfer efficiency remained comparable to that of other variants. Vaccine-induced nAbs were transferred more efficiently than infection-induced nAbs. Anti-spike receptor binding domain (RBD) IgG was associated with nAb against wild-type (Wuhan-Hu-1) following breakthrough infection. Both vaccination and infection-induced anti-RBD IgA, which was more durable than anti-nucleocapsid IgA. IgA response was attenuated in pregnancy compared to non-pregnant controls. These data provide additional evidence of augmentation of humoral immune responses in hybrid immunity in pregnancy.

The impact of vaccine type and booster dose on the magnitude and breadth of SARS-CoV-2-specific systemic and mucosal antibodies among COVID-19 vaccine recipients

The COVID-19 pandemic has had a major impact on global health and economy, which was significantly mitigated by the availability of COVID-19 vaccines. The levels of systemic and mucosal antibodies against SARS-CoV-2 correlated with protection. However, there is limited data on how vaccine type and booster doses affect mucosal antibody response, and how the breadth of mucosal and systemic antibodies compares. In this cross-sectional study, we compared the magnitude and breadth of mucosal and systemic antibodies in 108 individuals who received either the BNT162b2 (Pfizer) or CoronaVac (SinoVac) vaccine. We found that BNT162b2 (vs CoronaVac) or booster doses (vs two doses) were significantly associated with higher serum IgG levels, but were not significantly associated with salivary IgA levels, regardless of prior infection status. Among non-infected individuals, serum IgG, serum IgA and salivary IgG levels were significantly higher against the ancestral strain than the Omicron BA.2 sublineage, but salivary IgA levels did not differ between the strains. Salivary IgA had the weakest correlation with serum IgG (r = 0.34) compared with salivary IgG (r = 0.63) and serum IgA (r = 0.60). Our findings suggest that intramuscular COVID-19 vaccines elicit a distinct mucosal IgA response that differs from the systemic IgG response. As mucosal IgA independently correlates with protection, vaccine trials should include mucosal IgA as an outcome measure.

Protective mucosal SARS-CoV-2 antibodies in the majority of the general population in the Netherlands

Antibodies to SARS-CoV-2 on the mucosal surfaces of the respiratory tract are understood to contribute to protection against SARS-CoV-2 infection. We aimed to describe the prevalence, levels, and functionality of mucosal antibodies in the general Dutch population. Nasal samples were collected from 778 randomly selected participants, 1-90 years of age, nested within the nationwide prospective SARS-CoV-2 PIENTER corona serosurvey in the Netherlands. Spike-specific immunoglobulin (Ig)G was detected in the nasal samples of 94.6% (in case of the wild-type S1 variant) and 94.9% (Omicron BA.1) of the individuals, whereas 44.2% and 62.7% of the individuals were positive for wild-type and Omicron BA.1 S1 IgA, respectively. The lowest prevalence of mucosal antibodies was observed in children under 12 years of age. The prevalence and levels of IgA and IgG were higher in individuals with a history of SARS-CoV-2 infection. Mucosal antibodies inhibited the binding of Wuhan, Delta, and Omicron BA.1 receptor binding domain to human angiotensin-converting enzyme 2 in 94.4%, 95.4%, and 92.6% of the participants, respectively. Higher levels of mucosal antibodies were associated with a lower risk of future infection.

Minding the margins: Evaluating the impact of COVID-19 among Latinx and Black communities with optimal qualitative serological assessment tools

COVID-19 disproportionately affected minorities, while research barriers to engage underserved communities persist. Serological studies reveal infection and vaccination histories within these communities, however lack of consensus on downstream evaluation methods impede meta-analyses and dampen the broader public health impact. To reveal the impact of COVID-19 and vaccine uptake among diverse communities and to develop rigorous serological downstream evaluation methods, we engaged racial and ethnic minorities in Massachusetts in a cross-sectional study (April-July 2022), screened blood and saliva for SARS-CoV-2 and human endemic coronavirus (hCoV) antibodies by bead-based multiplex assay and point-of-care (POC) test and developed across-plate normalization and classification boundary methods for optimal qualitative serological assessments. Among 290 participants, 91.4% reported receiving at least one dose of a COVID-19 vaccine, while 41.7% reported past SARS-CoV-2 infections, which was confirmed by POC- and multiplex-based saliva and blood IgG seroprevalences. We found significant differences in antigen-specific IgA and IgG antibody outcomes and indication of cross-reactivity with hCoV OC43. Finally, 26.5% of participants reported lingering COVID-19 symptoms, mostly middle-aged Latinas. Hence, prolonged COVID-19 symptoms were common among our underserved population and require public health attention, despite high COVID-19 vaccine uptake. Saliva served as a less-invasive sample-type for IgG-based serosurveys and hCoV cross-reactivity needed to be evaluated for reliable SARS-CoV-2 serosurvey results. The use of the developed rigorous downstream qualitative serological assessment methods will help standardize serosurvey outcomes and meta-analyses for future serosurveys beyond SARS-CoV-2.

Intranasal SARS-CoV-2 Omicron variant vaccines elicit humoral and cellular mucosal immunity in female mice

BACKGROUND

In order to prevent the emergence and spread of future variants of concern of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), developing vaccines capable of stopping transmission is crucial. The SARS-CoV-2 vaccine NDV-HXP-S can be administered live intranasally (IN) and thus induce protective immunity in the upper respiratory tract. The vaccine is based on Newcastle disease virus (NDV) expressing a stabilised SARS-CoV-2 spike protein. NDV-HXP-S can be produced as influenza virus vaccine at low cost in embryonated chicken eggs.

METHODS

The NDV-HXP-S vaccine was genetically engineered to match the Omicron variants of concern (VOC) BA.1 and BA.5 and tested as an IN two or three dose vaccination regimen in female mice. Furthermore, female mice intramuscularly (IM) vaccinated with mRNA-lipid nanoparticles (LNPs) were IN boosted with NDV-HXP-S. Systemic humoral immunity, memory T cell responses in the lungs and spleens as well as immunoglobulin A (IgA) responses in distinct mucosal tissues were characterised.

FINDINGS

NDV-HXP-S Omicron variant vaccines elicited high mucosal IgA and serum IgG titers against respective SARS-CoV-2 VOC in female mice following IN administration and protected against challenge from matched variants. Additionally, antigen-specific memory B cells and local T cell responses in the lungs were induced. Host immunity against the NDV vector did not interfere with boosting. Intramuscular vaccination with mRNA-LNPs was enhanced by IN NDV-HXP-S boosting resulting in improvement of serum neutralization titers and induction of mucosal immunity.

INTERPRETATION

We demonstrate that NDV-HXP-S Omicron variant vaccines utilised for primary immunizations or boosting efficiently elicit humoral and cellular immunity. The described induction of systemic and mucosal immunity has the potential to reduce infection and transmission.

FUNDING

This work was partially funded by the NIAIDCenters of Excellence for Influenza Research and Response (CEIRR) and by the NIAID Collaborative Vaccine Innovation Centers and by institutional funding from the Icahn School of Medicine at Mount Sinai. See under Acknowledgements for details.

SARS-CoV-2 Humoral and Cellular Immune Responses in People Living with HIV

Immunosuppressed individuals, such as people living with HIV (PLWH), remain vulnerable to severe COVID-19. We analyzed the persistence of specific SARS-CoV-2 humoral and cellular immune responses in a retrospective, cross-sectional study in PLWH on antiretroviral therapy. Among 104 participants, 70.2% had anti-S IgG antibodies, and 55.8% had significant neutralizing activity against the Omicron variant in a surrogate virus neutralization test. Only 38.5% were vaccinated (8.76 ± 4.1 months prior), all displaying anti-S IgG, 75% with neutralizing antibodies and anti-S IgA. Overall, 29.8% of PLWH had no SARS-CoV-2 serologic markers; they displayed significantly lower CD4 counts and higher HIV viral load. Severe immunosuppression (present in 12.5% of participants) was linked to lower levels of detectable anti-S IgG (p = 0.0003), anti-S IgA (p < 0.0001) and lack of neutralizing activity against the Omicron variant (p < 0.0001). T-cell responses were present in 86.7% of tested participants, even in those lacking serological markers. In PLWH without severe immunosuppression, neutralizing antibodies and T-cell responses persisted for up to 9 months post-infection or vaccination. Advanced immunosuppression led to diminished humoral immune responses but retained specific cellular immunity.

How effective is the BNT162b2 mRNA vaccine against SARS-CoV-2 transmission and infection? A national programme analysis in Monaco, July 2021 to September 2022

BACKGROUND

We quantified SARS-CoV-2 dynamics in different community settings and the direct and indirect effect of the BNT162b2 mRNA vaccine in Monaco for different variants of concern (VOC).

METHODS

Between July 2021 and September 2022, we prospectively investigated 20,443 contacts from 6320 index cases using data from the Monaco COVID-19 Public Health Programme. We calculated secondary attack rates (SARs) in households (n = 13,877), schools (n = 2508) and occupational (n = 6499) settings. We used binomial regression with a complementary log-log link function to measure adjusted hazard ratios (aHR) and vaccine effectiveness (aVE) for index cases to infect contacts and contacts to be infected in households.

RESULTS

In households, the SAR was 55% (95% CI 54-57) and 50% (48-51) among unvaccinated and vaccinated contacts, respectively. The SAR was 32% (28-36) and 12% (10-13) in workplaces, and 7% (6-9) and 6% (3-10) in schools, among unvaccinated and vaccinated contacts respectively. In household, the aHR was lower in contacts than in index cases (aHR 0.68 [0.55-0.83] and 0.93 [0.74-1.1] for delta; aHR 0.73 [0.66-0.81] and 0.89 [0.80-0.99] for omicron BA.1&2, respectively). Vaccination had no significant effect on either direct or indirect aVE for omicron BA.4&5. The direct aVE in contacts was 32% (17, 45) and 27% (19, 34), and for index cases the indirect aVE was 7% (- 17, 26) and 11% (1, 20) for delta and omicron BA.1&2, respectively. The greatest aVE was in contacts with a previous SARS-CoV-2 infection and a single vaccine dose during the omicron BA.1&2 period (45% [27, 59]), while the lowest were found in contacts with either three vaccine doses (aVE - 24% [- 63, 6]) or one single dose and a previous SARS-CoV-2 infection (aVE - 36% [- 198, 38]) during the omicron BA.4&5 period.

CONCLUSIONS

Protection conferred by the BNT162b2 mRNA vaccine against transmission and infection was low for delta and omicron BA.1&2, regardless of the number of vaccine doses and previous SARS-CoV-2 infection. There was no significant vaccine effect for omicron BA.4&5. Health authorities carrying out vaccination campaigns should bear in mind that the current generation of COVID-19 vaccines may not represent an effective tool in protecting individuals from either transmitting or acquiring SARS-CoV-2 infection.

Minding the margins: Evaluating the impact of COVID-19 among Latinx and Black communities with optimal qualitative serological assessment tools

COVID-19 disproportionately affected minorities, while research barriers to engage underserved communities persist. Serological studies reveal infection and vaccination histories within these communities, however lack of consensus on downstream evaluation methods impede meta-analyses and dampen the broader public health impact. To reveal the impact of COVID-19 and vaccine uptake among diverse communities and to develop rigorous serological downstream evaluation methods, we engaged racial and ethnic minorities in Massachusetts in a cross-sectional study (April - July 2022), screened blood and saliva for SARS-CoV-2 and human endemic coronavirus (hCoV) antibodies by bead-based multiplex assay and point-of-care (POC) test and developed across-plate normalization and classification boundary methods for optimal qualitative serological assessments. Among 290 participants, 91.4 % reported receiving at least one dose of a COVID-19 vaccine, while 41.7 % reported past SARS-CoV-2 infections, which was confirmed by POC- and multiplex-based saliva and blood IgG seroprevalences. We found significant differences in antigen-specific IgA and IgG antibody outcomes and indication of cross-reactivity with hCoV OC43. Finally, 26.5 % of participants reported lingering COVID-19 symptoms, mostly middle-aged Latinas. Hence, prolonged COVID-19 symptoms were common among our underserved population and require public health attention, despite high COVID-19 vaccine uptake. Saliva served as a less-invasive sample-type for IgG-based serosurveys and hCoV cross-reactivity needed to be evaluated for reliable SARS-CoV-2 serosurvey results. Using the developed rigorous downstream qualitative serological assessment methods will help standardize serosurvey outcomes and meta-analyses for future serosurveys beyond SARS-CoV-2.

Intranasal vaccination with an NDV-vectored SARS-CoV-2 vaccine protects against Delta and Omicron challenges

The rapid development and deployment of vaccines following the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been estimated to have saved millions of lives. Despite their immense success, there remains a need for next-generation vaccination approaches for SARS-CoV-2 and future emerging coronaviruses and other respiratory viruses. Here we utilized a Newcastle Disease virus (NDV) vectored vaccine expressing the ancestral SARS-CoV-2 spike protein in a pre-fusion stabilized chimeric conformation (NDV-PFS). When delivered intranasally, NDV-PFS protected both Syrian hamsters and K18 mice against Delta and Omicron SARS-CoV-2 variants of concern. Additionally, intranasal vaccination induced robust, durable protection that was extended to 6 months post-vaccination. Overall, our data provide evidence that NDV-vectored vaccines represent a viable next-generation mucosal vaccination approach.

Antibody responses in blood and saliva post COVID-19 bivalent booster do not reveal an Omicron BA.4/BA.5- specific response

Introduction

Current SARS-CoV-2 strains continue to mutate and attempt to evade the antibody response elicited by previous exposures and vaccinations. In September of 2022, the first updated SARS-CoV-2 vaccines, designed to create immune responses specific for the variants circulating in 2022, were approved. These new vaccines, known commonly as the bivalent boost(er), include mRNA that encodes both the original Wuhan-Hu-1 spike protein as well as the spike protein specific to the Omicron BA.4 and BA.5 variants.

Methods

We recruited volunteers from University of Massachusetts student, faculty and staff members to provide samples of blood and saliva at four different time points, including pre-boost and three times post boost and analyzed samples for antibody production as well as neutralization of virus.

Results

Our data provide a comprehensive analysis of the antibody response following a single dose of the bivalent boost over a 6-month period and support previous findings that the response induced after the bivalent boost does not create a strong BA.4/BA.5-specific antibody response.

Conclusion

We found no evidence of a specific anti-BA.4/BA.5 response developing over time, including in a sub-population of individuals who become infected after a single dose of the bivalent booster. Additionally, we present data that support the use of saliva samples as a reliable alternative to blood for antibody detection against specific SARS-CoV-2 antigens.

Microfluidic particle counter visualizing mucosal antibodies against SARS-CoV-2 in the upper respiratory tract for rapid evaluation of immune protection

Mucosal antibodies in the upper respiratory tract are the earliest and most critical responders to prevent respiratory infections, providing an indication for the rapid evaluation of immune protection. Here, we report a microfluidic particle counter that directly visualizes mucosal antibody levels in nasal mucus. The mucosal anti-SARS-CoV-2 spike receptor binding domain (RBD) antibodies in nasal secretions first react with magnetic microparticles (MMPs) and polystyrene microparticles (PMPs) that are surface-modified to form a "MMPs-anti-spike RBD IgG-PMPs" complex when RBD is present. After magnetic separation and loading into the microfluidic particle counter, the free PMPs, which are reduced with increasing anti-spike RBD IgG antibody levels, are trapped by a microfluidic particle dam and accumulate in the trapping channel. A sensitive mode [limit of detection (LOD): 14.0 ng mL-1; sample-to-answer time: 70 min] and an equipment-free rapid mode (LOD: 37.4 ng mL-1; sample-to-answer time: 20 min) were achieved. Eighty-seven nasal secretion (NS) samples from vaccinees were analyzed using our microfluidic particle counter, and the results closely resemble those of the gold-standard enzyme-linked immunosorbent assay (ELISA). The analysis shows that higher antibody levels were found in convalescent volunteers compared to noninfected volunteers. Together, we demonstrate a rapid kit that directly indicates immune status, which can guide vaccine strategy for individuals and the government.

Unravelling influenza correlates of protection: lessons from human A/H1N1 Challenge

Mucosal immunity is important in protecting from upper respiratory tract influenza infection. Human challenge provides a unique model to define correlates of protection with baseline immune responses being correlated to the quantity and length of viral shedding and clinical outcomes. Here, we discuss recent work on mucosal and systemic correlates of protection (R. Bean, L. T. Giurgea, A. Han, L. Czajkowski, et al., mBio 15:e02372-23, 2024, https://doi.org/10.1128/mbio.02372-23) and place it in the context of previous work on mucosal immunity. We also discuss the importance of standardized assays to allow global comparison of relevant immune responses in defining correlates of protection. Correlates of protection are important for designing next-generation broadly protective influenza vaccines.

Detection of SARS-CoV-2-specific mucosal antibodies in saliva following concomitant COVID-19 and influenza vaccination in the ComFluCOV trial

The ComFluCOV trial randomized 679 participants to receive an age-appropriate influenza vaccine, or placebo, alongside their second COVID-19 vaccine. Concomitant administration was shown to be safe, and to preserve systemic immune responses to both vaccines. Here we report on a secondary outcome of the trial investigating SARS-CoV-2-specific mucosal antibody responses. Anti-spike IgG and IgA levels in saliva were measured with in-house ELISAs. Concomitant administration of an influenza vaccine did not affect salivary anti-spike IgG positivity rates to Pfizer/BioNTech BNT162b2 (99.1 cf. 95.6%), or AstraZeneca ChAdOx1 (67.8% cf. 64.9%), at 3-weeks post-vaccination relative to placebo. Furthermore, saliva IgG positively correlated with serum titres highlighting the potential utility of saliva for assessing differences in immunogenicity in future vaccine studies. Mucosal IgA was not detected in response to either COVID-19 vaccine, reinforcing the need for novel vaccines capable of inducing sterilising immunity or otherwise reducing transmission. The trial is registered as ISRCTN 14391248.

COVID-19 mRNA vaccines induce robust levels of IgG but limited amounts of IgA within the oronasopharynx of young children

Background

Understanding antibody responses to SARS-CoV-2 vaccination is crucial for refining COVID-19 immunization strategies. Generation of mucosal immune responses, including mucosal IgA, could be of potential benefit to vaccine efficacy, yet limited evidence exists regarding the production of mucosal antibodies following the administration of current mRNA vaccines to young children.

Methods

We measured the levels of antibodies against SARS-CoV-2 from a cohort of children under 5 years of age undergoing SARS-CoV-2 mRNA vaccination (serially collected, matched serum and saliva samples, N=116) or on convenience samples of children under 5 years of age presenting to a pediatric emergency department (nasal swabs, N=103). Further, we assessed salivary and nasal samples for the ability to induce SARS-CoV-2 spike-mediated neutrophil extracellular traps (NET) formation.

Results

Longitudinal analysis of post-vaccine responses in saliva revealed the induction of SARS-CoV-2 specific IgG but not IgA. Similarly, SARS-CoV-2 specific IgA was only observed in nasal samples obtained from previously infected children with or without vaccination, but not in vaccinated children without a history of infection. In addition, oronasopharyngeal samples obtained from children with prior infection were able to trigger enhanced spike-mediated NET formation, and IgA played a key role in driving this process.

Conclusions

Despite the induction of specific IgG in the oronasal mucosa, current intramuscular vaccines have limited ability to generate mucosal IgA in young children. These results confirm the independence of mucosal IgA responses from systemic humoral responses following mRNA vaccination and suggest potential future vaccination strategies for enhancing mucosal protection in this young age group.

Investigation of Nasal Mucosal IgA Responses in the Population Following COVID-19 Pandemic - China, September 2022-August 2023

What is already known about this topic?

Mucosal IgA plays a crucial role in host immunity against respiratory viruses. Recent studies suggest that it has the potential to mitigate the transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant. However, a comprehensive population-based analysis examining mucosal IgA levels following the winter 2022 wave of the coronavirus disease 2019 (COVID-19) pandemic is yet to be conducted.

What is added by this report?

In our study involving 3,421 participants, we documented IgA responses subsequent to SARS-CoV-2 infection. A significant proportion of individuals sustained increased levels of IgA for over six months. These levels were also observed in individuals with prior infections who underwent asymptomatic reinfections, indicating an active production of IgA antibodies. Further, individuals with multiple vaccinations or severe symptoms tended to display elevated IgA levels after recovery.

What are the implications for public health practice?

IgA in the nasal mucosa is crucial for defense against SARS-CoV-2 infection. These insights can enhance our knowledge of immune responses following infection and have provided certain reference values for disease prevention and control strategies.

Comparison of Omicron breakthrough infection versus monovalent SARS-CoV-2 intramuscular booster reveals differences in mucosal and systemic humoral immunity

Our understanding of the quality of cellular and humoral immunity conferred by COVID-19 vaccination alone versus vaccination plus SARS-CoV-2 breakthrough (BT) infection remains incomplete. While the current (2023) SARS-CoV-2 immune landscape of Canadians is complex, in late 2021 most Canadians had either just received a third dose of COVID-19 vaccine, or had received their two-dose primary series and then experienced an Omicron BT. Herein we took advantage of this coincident timing to contrast cellular and humoral immunity conferred by three doses of vaccine versus two doses plus BT. Our results show thatBT infection induces cell-mediated immune responses to variants comparable to an intramuscular vaccine booster dose. In contrast, BT subjects had higher salivary immunoglobulin (Ig)G and IgA levels against the Omicron spike and enhanced reactivity to the ancestral spike for the IgA isotype, which also reacted with SARS-CoV-1. Serumneutralizing antibody levels against the ancestral strain and the variants were also higher after BT infection. Our results support the need for the development of intranasal vaccines that could emulate the enhanced mucosal and humoral immunity induced by Omicron BT without exposing individuals to the risks associated with SARS-CoV-2 infection.

Serum and Salivary IgG and IgA Response After COVID-19 Messenger RNA Vaccination

Importance

There is still considerable controversy in the literature regarding the capacity of intramuscular messenger RNA (mRNA) vaccination to induce a mucosal immune response.

Objective

To compare serum and salivary IgG and IgA levels among mRNA-vaccinated individuals with or without previous SARS-CoV-2 infection.

Design, Setting, and Participants

In this cohort study, SARS-CoV-2-naive participants and those with previous infection were consecutively included in the CoviCompare P and CoviCompare M mRNA vaccination trials and followed up to day 180 after vaccination with either the BNT162b2 (Pfizer-BioNTech) vaccine or the mRNA-1273 (Moderna) vaccine at the beginning of the COVID-19 vaccination campaign (from February 19 to June 8, 2021) in France. Data were analyzed from October 25, 2022, to July 13, 2023.

Main Outcomes and Measures

An ultrasensitive digital enzyme-linked immunosorbent assay was used for the comparison of SARS-CoV-2 spike-specific serum and salivary IgG and IgA levels. Spike-specific secretory IgA level was also quantified at selected times.

Results

A total of 427 individuals were included in 3 groups: participants with SARS-CoV-2 prior to vaccination who received 1 single dose of BNT162b2 (Pfizer-BioNTech) (n = 120) and SARS-CoV-2-naive individuals who received 2 doses of mRNA-1273 (Moderna) (n = 172) or 2 doses of BNT162b2 (Pfizer-BioNTech) (n = 135). The median age was 68 (IQR, 39-75) years, and 228 (53.4%) were men. SARS-CoV-2 spike-specific IgG saliva levels increased after 1 or 2 vaccine injections in individuals with previous infection and SARS-CoV-2-naive individuals. After vaccination, SARS-CoV-2-specific saliva IgA levels, normalized with respect to total IgA levels, were significantly higher in participants with previous infection, as compared with the most responsive mRNA-1273 (Moderna) recipients (median normalized levels, 155 × 10-5 vs 37 × 10-5 at day 29; 107 × 10-5 vs 54 × 10-5 at day 57; and 104 × 10-5 vs 70 × 10-5 at day 180 [P < .001]). In contrast, compared with day 1, spike-specific IgA levels in the BNT162b2-vaccinated SARS-CoV-2-naive group increased only at day 57 (36 × 10-5 vs 49 × 10-5 [P = .01]). Bona fide multimeric secretory IgA levels were significantly higher in individuals with previous infection compared with SARS-CoV-2-naive individuals after 2 antigenic stimulations (median optical density, 0.36 [IQR, 0.16-0.63] vs 0.16 [IQR, 0.10-0.22]; P < .001).

Conclusions and Relevance

The findings of this cohort study suggest that mRNA vaccination was associated with mucosal immunity in individuals without prior SARS-CoV-2 infection, but at much lower levels than in previously infected individuals. Further studies are needed to determine the association between specific saliva IgA levels and prevention of infection or transmission.

SARS-CoV-2-specific mucosal immune response in vaccinated versus infected children

The anti-COVID-19 intramuscular vaccination induces a strong systemic but a weak mucosal immune response in adults. Little is known about the mucosal immune response in children infected or vaccinated against SARS-CoV-2. We found that 28% of children had detectable salivary IgA against SARS-CoV-2 even before vaccination, suggesting that, in children, SARS-CoV-2 infection may be undiagnosed. After vaccination, only receptor-binding domain (RBD)-specific IgA1 significantly increased in the saliva. Conversely, infected children had significantly higher salivary RBD-IgA2 compared to IgA1, indicating that infection more than vaccination induces a specific mucosal immune response in children. Future efforts should focus on development of vaccine technologies that also activate mucosal immunity.

SARS-CoV-2 infection induces robust mucosal antibody responses in the upper respiratory tract

Despite multiple research efforts to characterize coronavirus disease 2019 (COVID-19) in humans, there is no clear data on the specific role of mucosal immunity on COVID-19 disease. Here, we longitudinally profile the antibody response against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and seasonal HCoV-OC43 S proteins in serum and nasopharyngeal swabs from COVID-19 patients. Results showed that specific antibody responses against SARS-CoV-2 and HCoV-OC43 S proteins can be detected in the upper respiratory tract. We found that COVID-19 patients mounted a robust mucosal antibody response against SARS-CoV-2 S with specific secretory immunoglobulin A (sIgA), IgA, IgG, and IgM antibody subtypes detected in the nasal swabs. Additionally, COVID-19 patients showed IgG, IgA, and sIgA responses against HCoV-OC43 S in the local mucosa, whereas no specific IgM was detected. Interestingly, mucosal antibody titers against SARS-CoV-2 peaked at day 7, whereas HCoV-OC43 titers peaked earlier at day 3 post-recruitment, suggesting an immune memory recall to conserved epitopes of beta-HCoVs in the upper respiratory tract.

Comparison of SARS-CoV-2 spike-specific IgA and IgG in nasal secretions, saliva and serum

Introduction

Several novel vaccine platforms aim at mucosal immunity in the respiratory tract to block SARS-CoV-2 transmission. Standardized methods for mucosal sample collection and quantification of mucosal antibodies are therefore urgently needed for harmonized comparisons and interpretations across mucosal vaccine trials and real-world data.

Methods

Using commercial electrochemiluminescence antibody panels, we compared SARS-CoV-2 spike-specific IgA and IgG in paired saliva, nasal secretions, and serum from 1048 healthcare workers with and without prior infection.

Results

Spike-specific IgA correlated well in nasal secretions and saliva (r>0.65, p<0.0001), but the levels were more than three-fold higher in nasal secretions as compared to in saliva (p<0.01). Correlations between the total population of spike-specific IgA and spike-specific secretory IgA (SIgA) were significantly stronger (p<0.0001) in nasal secretions (r=0.96, p<0.0001) as opposed to in saliva (r=0.77, p<0.0001), and spike-specific IgA correlated stronger (p<0.0001) between serum and saliva (r=0.73, p<0.001) as opposed to between serum and nasal secretions (r=0.54, p<0.001), suggesting transudation of monomeric spike specific IgA from the circulation to saliva. Notably, spike-specific SIgA had a markedly higher SARS-CoV-2 variant cross-binding capacity as compared to the total population of spike specific IgA and IgG in both nasal secretions, saliva and serum, (all p<0.0001), which emphasizes the importance of taking potential serum derived monomeric IgA into consideration when investigating mucosal immune responses.

Discussion

Taken together, although spike-specific IgA can be reliably measured in both nasal secretions and saliva, our findings imply an advantage of higher levels and likely also a larger proportion of SIgA in nasal secretions as compared to in saliva. We further corroborate the superior variant cross-binding capacity of SIgA in mucosal secretions, highlighting the potential protective benefits of a vaccine targeting the upper respiratory tract.

SARS-CoV-2-infection- and vaccine-induced antibody responses are long lasting with an initial waning phase followed by a stabilization phase

It is thought that mRNA-based vaccine-induced immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wanes quickly, based mostly on short-term studies. Here, we analyzed the kinetics and durability of the humoral responses to SARS-CoV-2 infection and vaccination using >8,000 longitudinal samples collected over a 3-year period in New York City. Upon primary immunization, participants with pre-existing immunity mounted higher antibody responses faster and achieved higher steady-state antibody titers than naive individuals. Antibody kinetics were characterized by two phases: an initial rapid decay, followed by a stabilization phase with very slow decay. Booster vaccination equalized the differences in antibody concentration between participants with and without hybrid immunity, but the peak antibody titers decreased with each successive antigen exposure. Breakthrough infections increased antibodies to similar titers as an additional vaccine dose in naive individuals. Our study provides strong evidence that SARS-CoV-2 antibody responses are long lasting, with initial waning followed by stabilization.