The continuous emergence of SARS-CoV-2 variants highlights the need of developing vaccines with broad protection. Here, according to the immune-escape capability and evolutionary convergence, the representative SARS-CoV-2 strains carrying the hotspot mutations were selected. Then, guided by structural and computational analyses, we present a mutation-integrated trimeric form of spike receptor-binding domain (mutI-tri-RBD) as a broadly protective vaccine candidate, which combined heterologous RBDs from different representative strains into a hybrid immunogen and integrated immune-escape hotspots into a single antigen. When compared with a homo-tri-RBD vaccine candidate in the stage of phase II trial, of which all three RBDs are derived from the SARS-CoV-2 prototype strain, mutI-tri-RBD induced significantly higher neutralizing antibody titers against the Delta and Beta variants, and maintained a similar immune response against the prototype strain. Pseudo-virus neutralization assay demonstrated that mutI-tri-RBD also induced broadly strong neutralizing activities against all tested 23 SARS-CoV-2 variants. The in vivo protective capability of mutI-tri-RBD was further validated in hACE2-transgenic mice challenged by the live virus, and the results showed that mutI-tri-RBD provided potent protection not only against the SARS-CoV-2 prototype strain but also against the Delta and Beta variants.

Safe and effective vaccines are still urgently needed to cope with the ongoing COVID-19 pandemic. Recently, we developed a recombinant COVID-19 vaccine (V-01) containing fusion protein (IFN-PADRE-RBD-Fc dimer) as antigen verified to induce protective immunity against SARS-CoV-2 challenge in pre-clinical study, which supported progression to Phase I clinical trials in humans. A Randomized, double-blind, placebo-controlled Phase I clinical trial was initiated at the Guangdong Provincial Center for Disease Control and Prevention (Gaozhou, China) in February 2021. Healthy adults aged between 18 and 59 years and over 60 years were sequentially enrolled and randomly allocated into three subgroups (1:1:1) either to receive the vaccine (10, 25, and 50 μg) or placebo (V-01: Placebo = 4:1) intramuscularly with a 21-day interval by a sentinel and dose escalation design. The data showed a promising safety profile with approximately 25% vaccine-related overall adverse events (AEs) within 30 days and no grade 3 or worse AEs. Besides, V-01 provoked rapid and strong immune responses, elicited substantially high-titre neutralizing antibodies and anti-RBD IgG peaked at day 35 or 49 after first dose, presented with encouraging immunogenicity at low dose (10 μg) subgroup and elderly participants, which showed great promise to be used as all-aged (18 and above) vaccine against COVID-19. Taken together, our preliminary findings indicate that V-01 is safe and well tolerated, capable of inducing rapid and strong immune responses, and warrants further testing in Phase II/III clinical trials.

Chronic hepatitis B virus (HBV) infection poses a major global health challenge with massive morbidity and mortality. Despite a preventive vaccine, current treatments provide limited virus clearance, necessitating lifelong commitment. The HBV surface antigen (HBsAg) is crucial for diagnosis and prognosis, yet its high-resolution structure and assembly on the virus envelope remain elusive. Utilizing extensive datasets and advanced cryo–electron microscopy analysis, we present structural insights into HBsAg at a near-atomic resolution of 3.7 angstroms. HBsAg homodimers assemble into subviral particles with D ₂ - and D ₄ -like quasisymmetry, elucidating the dense-packing rules and structural adaptability of HBsAg. These findings provide insights into how HBsAg assembles into higher-order filaments and interacts with the capsid to form virions.

Background: Innovative coronavirus disease 2019 (COVID-19) vaccines, with elevated global manufacturing capacity, enhanced safety and efficacy, simplified dosing regimens, and distribution that is less cold chain-dependent, are still global imperatives for tackling the ongoing pandemic. A previous phase I trial indicated that the recombinant COVID-19 vaccine (V-01), which contains a fusion protein (IFN-PADRE-RBD-Fc dimer) as its antigen, is safe and well tolerated, capable of inducing rapid and robust immune responses, and warranted further testing in additional clinical trials. Herein, we aimed to assess the immunogenicity and safety of V-01, providing rationales of appropriate dose regimen for further efficacy study. Methods: A randomized, double-blind, placebo-controlled phase II clinical trial was initiated at the Gaozhou Municipal Centre for Disease Control and Prevention (Guangdong, China) in March 2021. Both younger (n = 440; 18–59 years of age) and older (n = 440; ≥60 years of age) adult participants in this trial were sequentially recruited into two distinct groups: two-dose regimen group in which participants were randomized either to follow a 10 or 25 μg of V-01 or placebo given intramuscularly 21 days apart (allocation ratio, 3:3:1, n = 120, 120, 40 for each regimen, respectively), or one-dose regimen groups in which participants were randomized either to receive a single injection of 50 μg of V-01 or placebo (allocation ratio, 3:1, n = 120, 40, respectively). The primary immunogenicity endpoints were the geometric mean titers of neutralizing antibodies against live severe acute respiratory syndrome coronavirus 2, and specific binding antibodies to the receptor binding domain (RBD). The primary safety endpoint evaluation was the frequencies and percentages of overall adverse events (AEs) within 30 days after full immunization. Results: V-01 provoked substantial immune responses in the two-dose group, achieving encouragingly high titers of neutralizing antibody and anti-RBD immunoglobulin, which peaked at day 35 (161.9 [95% confidence interval [CI]: 133.3–196.7] and 149.3 [95%CI: 123.9–179.9] in 10 and 25 μg V-01 group of younger adults, respectively; 111.6 [95%CI: 89.6–139.1] and 111.1 [95%CI: 89.2–138.4] in 10 and 25 μg V-01 group of older adults, respectively), and remained high at day 49 after a day-21 second dose; these levels significantly exceed those in convalescent serum from symptomatic COVID-19 patients (53.6, 95%CI: 31.3–91.7). Our preliminary data show that V-01 is safe and well tolerated, with reactogenicity predominantly being absent or mild in severity and only one vaccine-related grade 3 or worse AE being observed within 30 days. The older adult participants demonstrated a more favorable safety profile compared with those in the younger adult group: with AEs percentages of 19.2%, 25.8%, 17.5% in older adults vs. 34.2%, 23.3%, 26.7% in younger adults at the 10, 25 μg V-01 two-dose group, and 50 μg V-01 one-dose group, respectively. Conclusions: The vaccine candidate V-01 appears to be safe and immunogenic. The preliminary findings support the advancement of the two-dose, 10 μg V-01 regimen to a phase III trial for a large-scale population-based evaluation of safety and efficacy. Trial Registration: http://www.chictr.org.cn/index.aspx (No. ChiCTR2100045107, http://www.chictr.org.cn/showproj.aspx?proj=124702).

Emerging SARS-CoV-2 variants are the most serious problem for COVID-19 prophylaxis and treatment. To determine whether the SARS-CoV-2 vaccine strain should be updated following variant emergence like seasonal flu vaccine, the changed degree on antigenicity of SARS-CoV-2 variants and H3N2 flu vaccine strains was compared. The neutralization activities of Alpha, Beta and Gamma variants’ spike protein-immunized sera were analysed against the eight current epidemic variants and 20 possible variants combining the top 10 prevalent RBD mutations based on the Delta variant, which were constructed using pseudotyped viruses. Meanwhile, the neutralization activities of convalescent sera and current inactivated and recombinant protein vaccine-elicited sera were also examined against all possible Delta variants. Eight HA protein-expressing DNAs elicited-animal sera were also tested against eight pseudotyped viruses of H3N2 flu vaccine strains from 2011–2019. Our results indicate that the antigenicity changes of possible Delta variants were mostly within four folds, whereas the antigenicity changes among different H3N2 vaccine strains were approximately 10–100-fold. Structural analysis of the antigenic characterization of the SARS-CoV-2 and H3N2 mutations supports the neutralization results. This study indicates that the antigenicity changes of the current SARS-CoV-2 may not be sufficient to require replacement of the current vaccine strain.

Summary: Background: A safe and effective coronavirus disease 2019 (COVID-19) vaccine is urgently needed to control the ongoing pandemic. Although progress has been made recently with several candidates reporting positive efficacy results, COVID-19 vaccines developed so far cannot meet the global vaccine demand. We developed a protein subunit vaccine against COVID-19, using dimeric form of receptor-binding domain (RBD) as the antigen. We aimed to assess the safety and immunogenicity of this vaccine in humans and determine the appropriate dose and schedule for an efficacy study. Methods: We did two randomized, double-blind, placebo-controlled, phase 1 and 2 trials for an RBD-based protein subunit vaccine, ZF2001. In phase 1 study, 50 healthy adults aged 18-59 years were enrolled and randomly allocated to three groups to receive three doses of vaccine (25 μg or 50 μg RBD-dimer, with adjuvant) or placebo (adjuvant-only) intramuscularly, 30 days apart. In phase 2 study, 900 healthy adults aged 18-59 years were enrolled and randomly allocated to six groups to receive vaccine (25 μg or 50 μg RBD-dimer, with adjuvant) or placebo (adjuvant-only) intramuscularly, with the former 3 groups given two doses and the latter 3 groups given three doses, 30 days apart. For phase 1 trial, the primary outcome was safety, as measured by the occurrence of adverse events and serious adverse events. The secondary outcome was immunogenicity as measured by the seroconversion rate and magnitude of antigen-binding antibodies, neutralizing antibodies and T-cell cytokine production. For phase 2 trial, the primary outcome included both safety and immunogenicity. These trials are registered with ClinicaTrials.gov, NCT04445194 and NCT04466085 . Findings: Between June 22 and September 15, 2020, 50 participants were enrolled to the phase 1 study (mean age 32.6 years) and 900 participants were enrolled to phase 2 study (mean age 43.5 years), to receive vaccine or placebo with a two-dose or three-dose schedule. For both trials, local and systemic adverse reactions were absent or mild in most participants. There were no serious adverse events related to vaccine in either trial. After three doses, neutralizing antibodies were detected in all participants receiving either 25 μg or 50 μg dose of vaccine in phase 1 study, and in 97% (the 25 μg group) and 93% (the 50 μg group) of participants, respectively, in phase 2 study. The SARS-CoV-2-neutralizing geometric mean titres (GMTs) were 94.5 for the 25 μg group and 117.8 for the 50 μg group in phase 1, and 102.5 for the 25 μg group and 69.1 for the 50 μg group in phase 2, exceeding the level of a panel of COVID-19 convalescent samples (GMT, 51). Vaccine induced balanced T _H 1 and T _H 2 responses. The 50 μg group did not show enhanced immunogenicity compared with the 25 μg group. Interpretation: The protein subunit vaccine ZF2001 is well-tolerated and immunogenic. The safety and immunogenicity data from phase 1 and 2 trials for ZF2001 support the use of 25 μg vaccine dose with three-dose schedule to an ongoing phase 3 large-scale evaluation for safety and efficacy. Funding: National Program on Key Research Project of China, National Science and Technology Major Projects of Drug Discovery, Strategic Priority Research Program of the Chinese Academy of Sciences, and Anhui Zhifei Longcom Biopharmaceutical.