Inside-out assembly of viral antigens for the enhanced vaccination.

Current attempts in vaccine delivery systems concentrate on replicating the natural dissemination of live pathogens, but neglect that pathogens evolve to evade the immune system rather than to provoke it. In the case of enveloped RNA viruses, it is the natural dissemination of nucleocapsid protein (NP, core antigen) and surface antigen that delays NP exposure to immune surveillance. Here, we report a multi-layered aluminum hydroxide-stabilized emulsion (MASE) to dictate the delivery sequence of the antigens. In this manner, the receptor-binding domain (RBD, surface antigen) of the spike protein was trapped inside the nanocavity, while NP was absorbed on the outside of the droplets, enabling the burst release of NP before RBD. Compared with the natural packaging strategy, the inside-out strategy induced potent type I interferon-mediated innate immune responses and triggered an immune-potentiated environment in advance, which subsequently boosted CD40+ DC activations and the engagement of the lymph nodes. In both H1N1 influenza and SARS-CoV-2 vaccines, rMASE significantly increased antigen-specific antibody secretion, memory T cell engagement, and Th1-biased immune response, which diminished viral loads after lethal challenge. By simply reversing the delivery sequence of the surface antigen and core antigen, the inside-out strategy may offer major implications for enhanced vaccinations against the enveloped RNA virus.

Effect of adjuvanting RBD-dimer-based subunit COVID-19 vaccines with Sepivac SWE™.

Protein subunit vaccines have been widely used to combat infectious diseases, including the current COVID-19 pandemic. Adjuvants play the key role in shaping the quality and magnitude of the immune response to protein and inactivated vaccines. We previously developed a protein subunit COVID-19 vaccine, termed ZF2001, based on an aluminium hydroxide-adjuvanted tandem-repeat dimeric receptor-binding domain (RBD) of the viral spike (S) protein. Here, we described the use of a squalene-based oil-in-water adjuvant, Sepivac SWE™ (abbreviated to SWE), to further improve the immunogenicity of this RBD-dimer-based subunit vaccines. Compared with ZF2001, SWE adjuvant enhanced the antibody and CD4+ T-cell responses in mice with at least 10 fold of dose sparing compared with ZF2001 adjuvanted with aluminium hydroxide. SWE-adjuvanted vaccine protected mice against SARS-CoV-2 challenge. To ensure adequate protection against the currently circulating Omicron variant, we evaluated this adjuvant in combination with Delta-Omicron chimeric RBD-dimer. SWE significantly increased antibody responses compared with aluminium hydroxide adjuvant and afforded greater neutralization breadth. These data highlight the advantage of emulsion-based adjuvants to elevate the protective immune response of protein subunit COVID-19 vaccines.

A systematic review and meta-analysis of the effectiveness and safety of COVID-19 vaccination in older adults.

In the coronavirus disease 2019 (COVID-19) pandemic, vaccinations were essential in preventing COVID-19 infections and related mortality in older adults. The objectives of this study were to evaluate the effectiveness and safety of the COVID-19 vaccines in older adults. We systematically searched the electronic bibliographic databases of PubMed, Web of Science, Embase, Cochrane Library, ClinicalTrials.gov, Research Square, and OpenGrey, as well as other sources of gray literature, for studies published between January 1, 2020, and October 1, 2022. We retrieved 22 randomized controlled trials (RCTs), with a total of 3,404,696 older adults (aged over 60 years) participating, that were included in the meta-analysis. No significant publication bias was found. In the cumulative meta-analysis, we found that the COVID-19 vaccines were effective in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (OR = 0.38, 95% CI = 0.23-0.65, p = 0.0004) and in reducing the number of COVID-19-related deaths (OR = 0.16, 95% CI = 0.10-0.25, p < 0.00001) in elderly people. Antibody seroconversion (AS) and geometric mean titer (GMT) levels significantly increased in vaccinated older adults [OR = 24.42, 95% CI = 19.29-30.92; standardized mean difference (SMD) = 0.92, 95% CI = 0.64-1.20, respectively]. However, local and systemic adverse events after COVID-19 vaccine administration were found in older adults (OR = 2.57, 95% CI = 1.83-3.62, p < 0.00001). Although vaccination might induce certain adverse reactions in the elderly population, the available evidence showed that the COVID-19 vaccines are effective and tolerated, as shown by the decrease in COVID-19-related deaths in older adults. It needs to be made abundantly clear to elderly people that the advantages of vaccination far outweigh any potential risks. Therefore, COVID-19 vaccination should be considered as the recommended strategy for the control of this disease by preventing SARS-CoV-2 infection and related deaths in older adults. More RCTs are needed to increase the certainty of the evidence and to verify our conclusions. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022319698, identifier CRD42022319698.

A systematic review and meta-analysis of the effectiveness and safety of COVID-19 vaccination in older adults

In the coronavirus disease 2019 (COVID-19) pandemic, vaccinations were essential in preventing COVID-19 infections and related mortality in older adults. The objectives of this study were to evaluate the effectiveness and safety of the COVID-19 vaccines in older adults. We systematically searched the electronic bibliographic databases of PubMed, Web of Science, Embase, Cochrane Library, ClinicalTrials.gov, Research Square, and OpenGrey, as well as other sources of gray literature, for studies published between January 1, 2020, and October 1, 2022. We retrieved 22 randomized controlled trials (RCTs), with a total of 3,404,696 older adults (aged over 60 years) participating, that were included in the meta-analysis. No significant publication bias was found. In the cumulative meta-analysis, we found that the COVID-19 vaccines were effective in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (OR = 0.38, 95% CI = 0.23–0.65, p = 0.0004) and in reducing the number of COVID-19-related deaths (OR = 0.16, 95% CI = 0.10–0.25, p < 0.00001) in elderly people. Antibody seroconversion (AS) and geometric mean titer (GMT) levels significantly increased in vaccinated older adults [OR = 24.42, 95% CI = 19.29–30.92;standardized mean difference (SMD) = 0.92, 95% CI = 0.64–1.20, respectively]. However, local and systemic adverse events after COVID-19 vaccine administration were found in older adults (OR = 2.57, 95% CI = 1.83–3.62, p < 0.00001). Although vaccination might induce certain adverse reactions in the elderly population, the available evidence showed that the COVID-19 vaccines are effective and tolerated, as shown by the decrease in COVID-19-related deaths in older adults. It needs to be made abundantly clear to elderly people that the advantages of vaccination far outweigh any potential risks. Therefore, COVID-19 vaccination should be considered as the recommended strategy for the control of this disease by preventing SARS-CoV-2 infection and related deaths in older adults. More RCTs are needed to increase the certainty of the evidence and to verify our conclusions. Systematic review registration https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022319698, identifier CRD42022319698.

A booster of Delta-Omicron RBD-dimer protein subunit vaccine augments sera neutralization of Omicron sub-variants BA.1/BA.2/BA.2.12.1/BA.4/BA.5.

The SARS-CoV-2 Omicron variants of concern (VOCs) showed severe resistance to the early-approved COVID-19 vaccines-induced immune responses. The breakthrough infections by the Omicron VOCs are currently the major challenge for pandemic control. Therefore, booster vaccination is crucial to enhance immune responses and protective efficacy. Previously, we developed a protein subunit COVID-19 vaccine ZF2001, based on the immunogen of receptor-binding domain (RBD) homodimer, which was approved in China and other countries. To adapt SARS-CoV-2 variants, we further developed chimeric Delta-Omicron BA.1 RBD-dimer immunogen which induced broad immune responses against SARS-CoV-2 variants. In this study, we tested the boosting effect of this chimeric RBD-dimer vaccine in mice after priming with two doses of inactivated vaccines, compared with a booster of inactivated vaccine or ZF2001. The results demonstrated that boosting with bivalent Delta-Omicron BA.1 vaccine greatly promoted the neutralizing activity of the sera to all tested SARS-CoV-2 variants. Therefore, the Delta-Omicron chimeric RBD-dimer vaccine is a feasible booster for those with prior vaccination of COVID-19 inactivated vaccines.

Severe acute respiratory syndrome coronavirus 2 virus-like particles induce dendritic cell maturation and modulate T cell immunity.

Dendritic cells (DCs) are professional antigen-presenting cells that play an important role in both innate and acquired immune responses against pathogens. However, the role of DCs in coronavirus disease 2019 (COVID-19) is unclear. Virus-like particles (VLPs) that structurally mimic the original virus are one of the candidates COVID-19 vaccines. In the present study, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) VLPs were used as an alternative to live virus to evaluate the interaction of the virus with DCs. The results revealed that SARS-CoV-2 VLPs induced DC maturation by augmenting cell surface molecule expression (CD80, CD86, and major histocompatibility complex class II (MHC-II)) and inflammatory cytokine production (tumor necrosis factor-α, interleukin (IL)-1ß, IL-6, and IL-12p70) in DCs via the mitogen-activated protein kinase and nuclear factor-κB signaling pathways. In addition, mature DCs induced by SARS-CoV-2 VLPs promoted T cell proliferation, which was dependent on VLPs concentration. Our results suggest that SARS-CoV-2 VLPs regulate the immune response by interacting with DCs. These findings will improve the understanding of SARS-CoV-2 pathogenesis and SARS-CoV-2 vaccine development.

A Multi-Center Study on the Negative Psychological Impact and Associated Factors in Chinese Healthcare Workers 1 Year After the COVID-19 Initial Outbreak.

Objectives: The study aimed at analyzing the prevalence of five psychological outcomes (depression, anxiety, stress, post-traumatic stress disorder (PTSD), and suicidal ideation) among Chinese healthcare workers (HCWs), and measured the total possible negative psychological impact 1 year after the COVID-19 initial outbreak. Methods: A cross-sectional nationwide multi-center study was performed between November 2020 and March 2021 in China. A self-report questionnaire was applied, and three psychological scales were used. Binary logistic regression was performed to analyze the risk factors associated with each psychological outcome. Results: The findings demonstrated that the COVID-19 pandemic had a negative psychological impact on HCWs, which was still evident 1 year after the initial outbreak. Nurses showed higher depression and anxiety than other HCWs. Female gender, passive coping, long working hours, having a chronic disease, and experiencing violence, among other factors, were all risk factors for psychological impairment. Conclusion: Developing and promoting programs to improve mental health among HCWs, and identifying those who might need psychological support is still relevant 1 year after the initial outbreak.

Immunogenicity, efficacy and safety of COVID-19 vaccines: an update of data published by 31 December 2021.

The unprecedented coronavirus disease 2019 (COVID-19) pandemic has caused a disaster for public health in the last 2 years, without any sign of an ending. Various vaccines were developed rapidly as soon as the outbreak occurred. Clinical trials demonstrated the reactogenicity, immunogenicity and protection efficacy in humans, and some of the vaccines have been approved for clinical use. However, waves of infections such as the recently circulating Omicron variant still occur. Newly emerging variants, especially the variants of concern, and waning humoral responses pose serious challenges to the control of the COVID-19 pandemic. Previously, we summarized the humoral and cellular immunity, safety profiles and protection efficacy of COVID-19 vaccines with clinical data published by 21 May 2021. In this review, we summarize and update the published clinical data of COVID-19 vaccines and candidates up to December 31, 2021.

Protective prototype-Beta and Delta-Omicron chimeric RBD-dimer vaccines against SARS-CoV-2.

Breakthrough infections by SARS-CoV-2 variants become the global challenge for pandemic control. Previously, we developed the protein subunit vaccine ZF2001 based on the dimeric receptor-binding domain (RBD) of prototype SARS-CoV-2. Here, we developed a chimeric RBD-dimer vaccine approach to adapt SARS-CoV-2 variants. A prototype-Beta chimeric RBD-dimer was first designed to adapt the resistant Beta variant. Compared with its homotypic forms, the chimeric vaccine elicited broader sera neutralization of variants and conferred better protection in mice. The protection of the chimeric vaccine was further verified in macaques. This approach was generalized to develop Delta-Omicron chimeric RBD-dimer to adapt the currently prevalent variants. Again, the chimeric vaccine elicited broader sera neutralization of SARS-CoV-2 variants and conferred better protection against challenge by either Delta or Omicron SARS-CoV-2 in mice. The chimeric approach is applicable for rapid updating of immunogens, and our data supported the use of variant-adapted multivalent vaccine against circulating and emerging variants.

Heterologous prime-boost immunizations with chimpanzee adenoviral vectors elicit potent and protective immunity against SARS-CoV-2 infection.

A safe and effective vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to tackle the COVID-19 global pandemic. Here, we describe the development of chimpanzee adenovirus serotypes 6 and 68 (AdC6 and AdC68) vector-based vaccine candidates expressing the full-length transmembrane spike glycoprotein. We assessed the vaccine immunogenicity, protective efficacy, and immune cell profiles using single-cell RNA sequencing in mice. Mice were vaccinated via the intramuscular route with the two vaccine candidates using prime-only regimens or heterologous prime-boost regimens. Both chimpanzee adenovirus-based vaccines elicited strong and long-term antibody and T cell responses, balanced Th1/Th2 cell responses, robust germinal center responses, and provided effective protection against SARS-CoV-2 infection in mouse lungs. Strikingly, we found that heterologous prime-boost immunization induced higher titers of protective antibodies, and more spike-specific memory CD8+ T cells in mice. Potent neutralizing antibodies produced against the highly transmissible SARS-CoV-2 variants B.1.1.7 lineage (also known as N501Y.V1) and B.1.351 lineage (also known as N501Y.V2) were detectable in mouse sera over 6 months after prime immunization. Our results demonstrate that the heterologous prime-boost strategy with chimpanzee adenovirus-based vaccines is promising for further development to prevent SARS-CoV-2 infection.

A tandem-repeat dimeric RBD protein-based covid-19 vaccine zf2001 protects mice and nonhuman primates.

Safe, efficacious, and deployable vaccines are urgently needed to control COVID-19 in the large-scale vaccination campaigns. We report here the preclinical studies of an approved protein subunit vaccine against COVID-19, ZF2001, which contains tandem-repeat dimeric receptor-binding domain (RBD) protein with alum-based adjuvant. We assessed vaccine immunogenicity and efficacy in both mice and non-human primates (NHPs). ZF2001 induced high levels of RBD-binding and SARS-CoV-2 neutralizing antibody in both mice and non-human primates, and elicited balanced TH1/TH2 cellular responses in NHPs. Two doses of ZF2001 protected Ad-hACE2-transduced mice against SARS-CoV-2 infection, as detected by reduced viral RNA and relieved lung injuries. In NHPs, vaccination of either 25 µg or 50 µg ZF2001 prevented infection with SARS-CoV-2 in lung, trachea, and bronchi, with milder lung lesions. No evidence of disease enhancement was observed in both animal models. ZF2001 has been approved for emergency use in China, Uzbekistan, Indonesia, and Columbia. The high safety, immunogenicity, and protection efficacy in both mice and NHPs found in this preclinical study was consistent with the results in human clinical trials.

Humoral and cellular immunity and the safety of COVID-19 vaccines: a summary of data published by 21 May 2021.

Coronavirus disease 2019 (COVID-19) has caused millions of deaths, and serious consequences to public health, economies and societies. Rapid responses in vaccine development have taken place since the isolation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the release of the viral genome sequence. By 21 May 2021, 101 vaccines were under clinical trials, and published data were available for 18 of them. Clinical study results from some vaccines indicated good immunogenicity and acceptable reactogenicity. Here, we focus on these 18 vaccines that had published clinical data to dissect the induced humoral and cellular immune responses as well as their safety profiles and protection efficacy.

Recombinant chimpanzee adenovirus AdC7 expressing dimeric tandem-repeat spike protein RBD protects mice against COVID-19.

A safe and effective vaccine is urgently needed to control the unprecedented COVID-19 pandemic. Four adenovirus-vectored vaccines expressing spike (S) protein have been approved for use. Here, we generated several recombinant chimpanzee adenovirus (AdC7) vaccines expressing S, receptor-binding domain (RBD), or tandem-repeat dimeric RBD (RBD-tr2). We found vaccination via either intramuscular or intranasal route was highly immunogenic in mice to elicit both humoral and cellular immune responses. AdC7-RBD-tr2 showed higher antibody responses compared to either AdC7-S or AdC7-RBD. Intranasal administration of AdC7-RBD-tr2 additionally induced mucosal immunity with neutralizing activity in bronchoalveolar lavage fluid. Either single-dose or two-dose mucosal administration of AdC7-RBD-tr2 protected mice against SARS-CoV-2 challenge, with undetectable subgenomic RNA in lung and relieved lung injury. AdC7-RBD-tr2-elicted sera preserved the neutralizing activity against the circulating variants, especially the Delta variant. These results support AdC7-RBD-tr2 as a promising COVID-19 vaccine candidate.

Integrated gut virome and bacteriome dynamics in COVID-19 patients.

SARS-CoV-2 is the cause of the current global pandemic of COVID-19; this virus infects multiple organs, such as the lungs and gastrointestinal tract. The microbiome in these organs, including the bacteriome and virome, responds to infection and might also influence disease progression and treatment outcome. In a cohort of 13 COVID-19 patients in Beijing, China, we observed that the gut virome and bacteriome in the COVID-19 patients were notably different from those of five healthy controls. We identified a bacterial dysbiosis signature by observing reduced diversity and viral shifts in patients, and among the patients, the bacterial/viral compositions were different between patients of different severities, although these differences are not entirely distinguishable from the effect of antibiotics. Severe cases of COVID-19 exhibited a greater abundance of opportunistic pathogens but were depleted for butyrate-producing groups of bacteria compared with mild to moderate cases. We replicated our findings in a mouse COVID-19 model, confirmed virome differences and bacteriome dysbiosis due to SARS-CoV-2 infection, and observed that immune/infection-related genes were differentially expressed in gut epithelial cells during infection, possibly explaining the virome and bacteriome dynamics. Our results suggest that the components of the microbiome, including the bacteriome and virome, are affected by SARS-CoV-2 infections, while their compositional signatures could reflect or even contribute to disease severity and recovery processes.

A Universal Design of Betacoronavirus Vaccines against COVID-19, MERS, and SARS.

Vaccines are urgently needed to control the ongoing pandemic COVID-19 and previously emerging MERS/SARS caused by coronavirus (CoV) infections. The CoV spike receptor-binding domain (RBD) is an attractive vaccine target but is undermined by limited immunogenicity. We describe a dimeric form of MERS-CoV RBD that overcomes this limitation. The RBD-dimer significantly increased neutralizing antibody (NAb) titers compared to conventional monomeric form and protected mice against MERS-CoV infection. Crystal structure showed RBD-dimer fully exposed dual receptor-binding motifs, the major target for NAbs. Structure-guided design further yielded a stable version of RBD-dimer as a tandem repeat single-chain (RBD-sc-dimer) which retained the vaccine potency. We generalized this strategy to design vaccines against COVID-19 and SARS, achieving 10- to 100-fold enhancement of NAb titers. RBD-sc-dimers in pilot scale production yielded high yields, supporting their scalability for further clinical development. The framework of immunogen design can be universally applied to other beta-CoV vaccines to counter emerging threats.