Compared with inactivated vaccines, live attenuated vaccines can theoretically induce potent cellular and humoral responses through both exogenous and endogenous antigen-presentation pathways. However, the percentage of live virus particles in the final vaccine products can vary between manufacturers, potentially due to variations in production processes such as lysis and purification. Whether the live-to-dead viral particles ratio influences the resulting immune response pattern remains unclear. To address this question, we formulated varicella vaccines (VarV) mimicking high-viability and low-viability compositions and systematically analyzed the immune response they induced in mice. Surprisingly, the percentage of viable viral particles in VarV products appears to modulate immune polarization. Higher viability tended to be associated with stronger Th1-oriented cellular responses and more robust humoral immunity, contributing to an overall immune profile resembling that induced by endogenous antigen presentation. This finding supports incorporating virus viability into VarV quality control, in addition to conventional viral titers, to optimize vaccine-induced cellular immunity and long-term protection against VZV reactivation.

Respiratory syncytial virus (RSV) is a primary pathogen responsible for lower respiratory tract infections in both infants and the elderly. However, vaccine development has been consistently hampered by the risk of vaccine-enhanced disease (VED), while the role of the RSV attachment (G) glycoprotein has long been overlooked. Using an mRNA vaccine platform, this study systematically evaluated the roles of two critical RSV G protein domains—the central conserved domain (CCD) and the mucin-like domains—in mediating immune protection and VED. Results indicate that the mucin-like domains confer no protection and induce marked VED. Surprisingly, although CCD immunization elicits potent humoral immunity and significantly reduces viral load, it also induces Th2-biased responses and exacerbates pulmonary inflammation following RSV challenge. However, fusion of CCD with the receptor-binding domain (RBD) of SARS-CoV-2 in an mRNA vaccine (CCD + RBD) successfully redirected the Th2-biased immune responses toward a balanced Th1/Th2 profile, while significantly attenuating CCD-induced immunopathology. CD8⁺ T-cell depletion and adoptive-transfer experiments further supported a contribution of RBD-responsive CD8⁺ T cells to the reduction in pathology. These findings provide proof of concept that heterologous antigen fusion can reshape CCD-associated immunopathology in a BALB/c RSV challenge model.

The rapid advancement of respiratory syncytial virus (RSV) mRNA vaccines has created an urgent need for robust, standardized, and predictive potency evaluation systems. Currently, this field relies on diverse, non-standardized in vitro methods that lack quantitative correlations with in vivo immune protection. This poses significant challenges for vaccine process optimization, quality control, and regulatory review. This paper systematically analyzes the strengths and limitations of existing in vitro and in vivo assessment strategies, identifying a bottleneck in the current framework due to the absence of quantitative links between in vitro indicators and in vivo outcomes. It proposes that addressing these challenges hinges on establishing predictive in vitro–in vivo correlation (IVIVC). Furthermore, it outlines a feasible pathway for constructing such predictive models through the design of systematic experimental protocols and multivariate statistical analysis. Alignment with Quality by Design (QbD) principles, this strategy aims to transition potency evaluation from empirical exploration to a predictive, standardized framework, ultimately streamlining the lifecycle management of RSV mRNA vaccines.

BACKGROUND:Current Oka strain varicella vaccines are generally safe but may cause latent neuronal infections leading to herpes zoster in some vaccinees. A novel v7D candidate vaccine has been developed to prevent varicella and reduce these risks. METHODS:This randomized, double-blind, controlled, phase 2b clinical trial was conducted in Jiangsu, China. Healthy children 1-12 years old with no history of varicella infection or vaccination were enrolled and randomly assigned to 0-3-/6-month schedule for low/medium dose. Phase 2a participants (3-12 years of age) previously receiving low-/medium-/high-dose v7D or licensed vOka received a second dose in phase 2b (0-15-month schedule) for exploratory analysis. The primary outcome was immunogenicity via varicella-zoster virus immunoglobulin (Ig)G seroconversion and geometric mean titers at 30 and 90 days post-second vaccination. This study was registered on Chinese Clinical Trial Registry, ChiCTR2300068380. RESULTS:In the per-protocol analysis, IgG antibody response reached 100% seroconversion by day 30 after the second vaccination. Antibody levels were comparable among different vaccine groups under the same schedule at day 30 post-second vaccination. The occurrence of adverse reactions was similar among the different vaccine groups within the same schedule. Most adverse reactions were mild or moderate and resolved shortly. None of the serious adverse events were related to the vaccine. CONCLUSIONS:The 2-dose regimens of v7D vaccine demonstrated robust immune responses and excellent safety profiles. These findings warrant further evaluation of the safety advantages and efficacy v7D vaccine in the future.

The development of innovative vaccine platforms, including protein subunit and nucleic acid vaccines, has advanced rapidly and established new technical paradigms for infectious disease prophylaxis. Nonetheless, many next-generation vaccines display suboptimal intrinsic immunogenicity owing to restricted antigenic complexity, resulting in inadequate protective immunity when delivered without adjuvants. Aluminum-containing adjuvants, the most widely deployed clinical adjuvants, primarily potentiate humoral immunity but elicit modest cellular immune responses, thereby failing to satisfy the immunological demands of modern vaccine platforms. Moreover, standard vaccines often fail to confer robust protective immunity in immunocompromised individuals. Accordingly, the rational design and development of next-generation vaccine adjuvants are critical to expanding the clinical translation of innovative vaccines and enhancing immunogenicity in vulnerable populations. In recent years, multiple novel adjuvants have gained clinical approval; of these, Toll-like receptor 4 (TLR4) agonists—core immunostimulatory components of several licensed adjuvant systems—have exhibited potent immunomodulatory activity across diverse infectious disease indications. This review offers a comprehensive synthesis of contemporary TLR4-targeted adjuvants, emphasizing their evolutionary development, molecular mechanisms of action, and clinical translational landscape. We aim to furnish mechanistic insights and translational guidance for scientists optimizing current adjuvants and discovering new TLR4-based candidates.

Human metapneumovirus (HPMV) is a significant pathogen that causes lower respiratory tract infections. Given the weak immunogenicity thereof, and the few relevant studies, the utility of the viral membrane protein G as a vaccine remains controversial. In this study, the G extracellular domain (RMG) of HMPV was expressed either alone or fused with the cholera toxin B subunit (CTB) and "cross-reacting material 197" (CRM197) carrier proteins (giving G-CTB/G and CRM197), to enhance immunogenicity. The non-glycosylated G protein (REG) expressed in Escherichia coli served as a control. SDS-PAGE and anti-His tag Western blotting verified that each protein was successfully expressed and correctly identified. BALB/c mice were immunized with each protein and subjected to challenge with HMPV. The results showed that, although immunization with RMG alone failed to induce potent neutralizing antibodies, it modestly reduced viral loads in the lungs of mice. However, the pathological damage caused by lung inflammation was more aggravated than that of the control challenge group. The level of specific IgG antibody induced by the recombinant G-CTB was significantly higher than that elicited by RMG. Compared to the RMG group, the viral load in the lungs of the G-CTB group tended to be reduced. Also, the damage caused by lung inflammation was significantly alleviated. Our study proves that HMPV G may be a valuable antigen in terms of HMPV vaccine development and offers a promising strategy for modulating the immunogenicity and safety thereof.

Despite ongoing efforts to reduce the burden of herpes zoster (HZ), it remains a global health concern. This partly-blinded, randomised controlled, dose-escalation phase I trial (CTR20220088) assessed the safety and immunogenicity of LZ901, an alum-adjuvanted recombinant zoster vaccine developed locally in China. Between Jan 15 and Oct 31, 2022, 80 healthy adults aged 50–70 years without prior varicella/HZ infection or varicella vaccination were equally randomised to receive LZ901 (50μg or 100μg), placebo, or a positive-controlled (HZ/su, Shingrix®). The primary outcome was safety, evaluated by adverse events (AEs) within 30 days after each vaccination and serious adverse events (SAEs) from first vaccination to six months post-vaccination. Exploratory outcomes included immunogenicity, assessed via anti-gE antibody and anti-VZV IgG concentrations, and gE-specific CD4+ and CD8+ T-cell responses. Within 30 days post-full vaccination, the overall incidence of AEs was 55.00% in both LZ901 dose-level groups, lower than that in the positive-controlled group (100.00%); no vaccine-related SAEs were reported. The geometric mean fold-rise of anti-gE antibody was 34.04 (50μg) and 16.88 (100μg), versus 118.99 (positive-controlled) and 1.08 (placebo). CD4+ T-cell responses were observed in 85.00% (50μg) and 95.00% (100μg) of LZ901 recipients, compared with 80.00% in the positive-controlled group. These findings indicated that LZ901 is safe, well tolerated, and immunogenic in older adults, supporting further evaluation of the safety profile and efficacy of LZ901 as a zoster vaccine candidate.

The identification of poliovirus in stool samples post-Oral Poliovirus Vaccine (OPV) immunization is essential for implementing post-eradication monitoring of poliomyelitis. This research presents the inaugural assessment of the virus shedding rate and the genetic diversity of OPV shedding strains across different Inactivated Poliovirus Vaccine (IPV)-OPV sequential immunization schedules. Our findings revealed that the shedding rate of different serotypes in each sequential immunization groups peaked within 7 days following the initial administration of OPV, and then gradually decreased. Prior vaccination with OPV reduced the rate and shortened the duration of virus shedding. Additionally, we observed a slight increase in the shedding rate of type3 after the removal of type2 from trivalent oral poliovirus vaccine (tOPV). The comprehensive analysis of the whole-genome high-throughput sequencing results for the shedding strain revealed that the variation sites among samples from different sequential immunization groups were distributed throughout the entire genome. The mutation frequencies within the 5’NCR, 2 C, 3 A, 3 C, and 3D regions were elevated of type1 and type3, while type2 had higher frequencies within the 5’NCR, VP1 and 3D regions. Consequently, it is imperative to expedite the transition from OPV to IPV, and to discontinue OPV as soon as wild poliovirus strains and vaccine-derived poliovirus (VDPVs) are eliminated.

Human respiratory syncytial virus (RSV) remains the leading viral cause of severe lower respiratory tract disease in infants and young children worldwide. Despite decades of research, RSV vaccine development remains hindered by the lack of animal models that accurately recapitulate pediatric susceptibility and allow rigorous assessment of protective efficacy and safety. Recent studies have identified the human insulin-like growth factor 1 receptor (hIGF1R) as a critical host receptor that facilitates RSV fusion and entry. Using a novel conditional knock-in mouse model, lung-specific hIGF1R expression achieved through Ad5 vector transduction enables rapid generation of a pediatric-relevant mouse model, offering a promising route to close this gap. Following intranasal challenge with RSV A2 (1.62 × 105 TCID50), four-week-old Ad5-hIGF1R mice exhibited higher pulmonary viral loads, marked peribronchiolar and perivascular inflammation, interstitial thickening and a tendency toward alveolar wall coalescence compared with wild-type controls, thereby recapitulating severe pediatric RSV disease. Transcriptomic analysis revealed 12 chemokine genes, upregulated in RSV-infected lungs of Ad5-hIGF1R mice relative to mock controls, that are involved in immune-inflammatory pathways and may serve as practical biomarkers for detecting dysregulated host responses during vaccine or antiviral-drug assessment. Furthermore, A mid-dose prefusion F (pre-F) vaccination regimen significantly reduced viral loads and moderately attenuated neutrophil infiltration in the lungs of Ad5-hIGF1R mice. In summary, the young Ad5-hIGF1R mice demonstrate that hIGF1R expression enhances RSV replication and immunopathology in vivo. This model not only overcomes the limited RSV susceptibility of conventional young mice but also provides a platform for evaluating RSV vaccines.

Affordable HPV vaccines are needed to accelerate elimination of cervical cancer. We evaluated the efficacy, safety, and immunogenicity of a recombinant bivalent human papillomavirus (HPV) vaccine composed of L1 virus-like particles (VLPs) for HPV 16 and HPV18 (HPV-2), produced in Pichia pastoris, in healthy Chinese women aged 18–30 years. In this phase 3, double-blind, randomised, placebo-controlled trial conducted at 10 centres in China (Nov 2014–Jan 2020), participants were assigned 1:1 to receive three doses of HPV-2 or placebo at months 0, 2, and 6. The primary endpoint was efficacy against histopathology-confirmed cervical intraepithelial neoplasia grade 2 or higher (CIN2+) associated with HPV16/18 through 48 months. Secondary endpoints were safety (adverse events [AEs] within 1 month of any dose; serious AEs throughout follow-up) and immunogenicity (neutralising antibody titres and seroconversion at Month 7 in a predefined subset). Of 12,000 women enrolled, 11,999 received the first dose and 11,281 completed all three doses. Over 48 months, 17 CIN2 + cases occurred: 3 among vaccine recipients (n = 5190) versus 14 among placebo recipients (n = 5167), corresponding to vaccine efficacy of 78.6

The licensed adjuvanted recombinant glycoprotein E (gE) subunit vaccine (HZ/su) is highly effective against herpes zoster (HZ). This randomised, active-controlled, non-inferiority trial (ChiCTR2300079076) compared the immunogenicity and safety of a novel gE-Fc fusion protein vaccine candidate (LZ901) with HZ/su in 300 healthy adults aged ≥50 years without prior HZ vaccination in Wuxi, China. Participants received either two doses of LZ901 (30-day interval; n = 151) or HZ/su (60-day interval; n = 149). The primary outcomes was the proportion of participants with simultaneous positive responses to two or more cytokines (IFN-γ, IL-2, TNF-α, or CD40L) 30 days after the second dose (referred to as gE-specific CD42+/CD82+ T-cell responses). LZ901 demonstrated non-inferiority to HZ/su (margin > -10%) for both CD4+ and CD8+ T-cell responses. Significantly higher response rates were observed with LZ901 for CD42 + T-cell responses (83.0% [117/141] vs 58.1% [79/136]; p < 0.0001) and CD82 + T-cell responses (46.8% [66/141] vs 8.8% [12/136]; p < 0.0001). Adverse reactions were markedly lower with LZ901 (41.1% [62/151] vs 87.9% [131/149]; p < 0.0001), including grade 3 events (0.7% [1/151] vs 6.0% [9/149]). LZ901 induced superior cellular immunogenicity and exhibited a better safety profile than HZ/su in adults ≥50 years, supporting its potential as a promising HZ prevention candidate vaccine.

This study explored how polymorphisms in cell surface Toll-like receptors (TLRs) influence susceptibility to Bartonella and ectoparasite infections in striped hamsters. Among six TLR genes, four sites in TLR1, TLR4, and TLR10 genes were associated with Bartonella susceptibility, while twelve sites across TLR4, TLR5, and TLR10 contributed to flea resistance. Similarly, eleven sites in TLR5, TLR6, and TLR10 were linked to gamasid mite parasitism. Genetic polymorphism analysis revealed that when heterozygous or rare genotypes protected the host from infections, the polymorphisms of these sites in uninfected individuals exceeded that of the infected group. The distribution of these sites on the three-dimensional structure of TLRs varied. All Bartonella-related sites were in the extracellular domain, whereas some of those related to fleas and gamasid mites were located in other domains. This research highlights the importance of cell surface TLRs in immune regulation and provides insights into evolutionary dynamics in natural environments.

Respiratory syncytial virus (RSV) remains a significant global health threat, especially to infants, the elderly, and immunocompromised individuals. This review comprehensively explores the progress in RSV vaccine development, the immune evaluation methods, and immunological surrogate. The RSV fusion (F) protein, a primary target for vaccine development, has been engineered in prefusion conformation to elicit potent neutralizing antibodies, while the attachment (G) glycoprotein and other immunogens are also being explored to broaden immune responses. Advances in diverse vaccine platforms, ranging from live attenuated and protein subunit vaccines to cutting-edge mRNA- and nanoparticle-based formulations, highlight the field’s progress, yet challenges in balancing safety, immunogenicity, and durability persist. Central to these efforts is the identification and validation of immunological surrogates, which may serve as critical benchmarks for vaccine efficacy. Neutralizing antibody titers, multifunctional T cell responses, and B cell memory have emerged as key correlates of protection. However, the feasibility of these surrogates depends on their ability to predict clinical outcomes across diverse populations and settings. While neutralizing antibodies block the virus directly, T cell responses are essential for clearing infected cells and preventing severe disease, and B cell memory ensures long-term immunity. Integrating these immunological markers into a cohesive framework requires standardized assays, robust clinical validation, and an in-depth understanding of RSV-induced immune response.

The immune imprinting against SARS-CoV-2 subvariants that dynamically evolves through sequential vaccination and infection has been rarely studied. Using antigenic cartography and neutralizing antibody (NAb) profiling, we demonstrate that prototype-targeting vaccination followed by Delta/early Omicron breakthrough infections maintained dominant wild-type (WT)-focused immunity. However, XBB.1.5-adapted vaccination after BA.5 outbreaks shifted immune imprinting toward XBB.1.9.1, altering the antigenic landscape. NAb analysis revealed progressive WT-specific immunity enhancement through three-dose vaccination followed by BA.5 breakthrough infection (GMT: I-I = 35, I-I-I = 72, I-I-I-B5 = 807), followed by sharp decline after XBB reinfection (GMT: I-I-I-B5-XBB = 231), confirming XBB’s antigenic divergence. To investigate the relationship between population immune dynamics and XBB infection risk following the BA.5/BF.7 wave, we analyzed the immune status of XBB breakthrough-infected and uninfected individuals from May to June 2023 (5–7 months post-wave). Utilizing an infection model calibrated to NAb titers against XBB.1.9.1, we estimated the 50% protective NAb titer against XBB infection to be 1:12.6. Retrospective analysis revealed that 80.3% of the population fell below this threshold in mid-2023, aligning with subsequent XBB resurgence. However, only 33.8% exhibited sub-protective JN.1 titers (<12.6) by August 2024, explaining the absence of JN.1-driven endemicity. This longitudinal study maps the immune imprint transitions from WT dominance to XBB adaptation, providing critical insights into vaccine strategy optimization and emerging variant risk assessment. The work highlights how iterative immune exposures reshape population protection landscapes against evolving coronaviruses.

The continuous evolution and mutation of SARS-CoV-2 have highlighted the need for more effective vaccines. In this study, CpG, MF59-like, and Alum adjuvant Delta strain inactivated SARS-CoV-2 vaccines were prepared, and the immunogenicity of these vaccines in mice was evaluated. The Delta + MF59-like vaccine group produced the highest levels of S- and RBD-binding antibodies and live Delta virus neutralization levels after one shot of immunization, while mice in the Delta + Alum vaccine group had the highest levels of these antibodies after two doses, and the Delta + MF59-like and Delta + Alum vaccine groups produced high levels of cross-neutralization antibodies against prototype, Beta, and Gamma strain SARS-CoV-2 viruses. There was no significant decrease in neutralizing antibody levels in any vaccine group during the observation period. CpG, MF59-like, and Alum adjuvant Delta strain inactivated SARS-CoV-2 vaccines excited different antibody subtypes compared with unadjuvanted vaccines; the Delta + CpG vaccine group had a higher proportion of IgG2b antibodies, indicating bias towards Th1 immunity. The proportions of IgG1 and IgG2b in the Delta + MF59-like vaccine group were similar to those of the unadjuvanted vaccine. However, the Delta + Alum vaccine group had a higher proportion of IgG1 antibodies, indicating bias towards Th2 immunity. Antigen-specific cytokine secretion CD4/8+ T cells were analyzed. In conclusion, the results of this study show differences in the immune efficacy of CpG, MF59-like, and Alum adjuvant Delta strain inactivated SARS-CoV-2 vaccines in mice, which have significant implications for the selection strategy for vaccine adjuvants.

BACKGROUND:The Oka varicella vaccine strain remains neurovirulent and can establish lifelong latent infection, raising safety concerns about vaccine-related herpes zoster. In this study, we aimed to evaluate the immunogenicity and safety of a skin-attenuated and neuro-attenuated varicella vaccine candidate (v7D vaccine). METHODS:We did this randomised, double-blind, controlled, phase 2a clinical trial in Jiangsu, China. Healthy children aged 3-12 years with no history of varicella infection or vaccination were enrolled and randomly assigned (1:1:1:1) to receive a single subcutaneous injection of the v7D vaccine at 3·3 log10 plaque forming units (PFU; low-dose v7D group), 3·9 log10 PFU (medium-dose v7D group), and 4·2 log10 PFU (high-dose v7D group), or the positive control varicella vaccine (vOka vaccine group). All the participants, laboratory personnel, and investigators other than the vaccine preparation and management staff were masked to the vaccine allocation. The primary outcome was assessment of the geometric mean titres (GMTs) and seroconversion rates of anti-varicella zoster virus immunoglobulin G (IgG) induced by different dose groups of v7D vaccine at 0, 42, 60, and 90 days after vaccination in the per-protocol set for humoral immune response analysis. Safety was a secondary outcome, focusing on adverse events within 42 days post-vaccination, and serious adverse events within 6 months after vaccination. This study was registered on Chinese Clinical Trial Registry, ChiCTR2000034434. FINDINGS:On Aug 18-21, 2020, 842 eligible volunteers were enrolled and randomly assigned treatment. After three participants withdrew, 839 received a low dose (n=211), middle dose (n=210), or high dose (n=210) of v7D vaccine, or the vOka vaccine (n=208). In the per-protocol set for humoral immune response analysis, the anti-varicella zoster virus IgG antibody response was highest at day 90. At day 90, the seroconversion rates of the low-dose, medium-dose, and high-dose groups of v7D vaccine and the positive control vOka vaccine group were 100·0% (95% CI 95·8-100·0; 87 of 87 participants), 98·9% (93·8-100·0; 87 of 88 participants), 97·8% (92·4-99·7; 91 of 93 participants), and 96·4% (89·8-99·2; 80 of 83 participants), respectively; the GMTs corresponded to values of 30·8 (95% CI 26·2-36·0), 31·3 (26·7-36·6), 28·2 (23·9-33·2), and 38·5 (31·7-46·7). The v7D vaccine, at low dose and medium dose, elicited a humoral immune response similar to that of the vOka vaccine. However, the high-dose v7D vaccine induced a marginally lower GMT compared with the vOka vaccine at day 90 (p=0·027). In the per-protocol set, the three dose groups of the v7D vaccine induced a similar humoral immune response at each timepoint, with no statistically significant differences. The incidence of adverse reactions in the low-dose, medium-dose, and high-dose groups of v7D vaccine was significantly lower than that in the vOka vaccine group (17% [35 of 211 participants], 20% [41 of 210 participants], and 13% [27 of 210 participants] vs 24% [50 of 208 participants], respectively; p=0·025), especially local adverse reactions (10% [22 of 211 participants], 14% [30 of 210 participants] and 9% [18 of 210 participants] vs 18% [38 of 208 participants], respectively; p=0·016). None of the serious adverse events were vaccine related. INTERPRETATION:The three dose groups of the candidate v7D vaccine exhibit similar humoral immunogenicity to the vOka vaccine and are well tolerated. These findings encourage further investigations on two-dose vaccination schedules, efficacy, and the potential safety benefit of v7D vaccine in the future. FUNDING:The National Natural Science Foundation of China, CAMS Innovation Fund for Medical Sciences, the Fundamental Research Funds for the Central Universities, and Beijing Wantai. TRANSLATION:For the Chinese translation of the abstract see Supplementary Materials section.

Trivalent oral poliovirus vaccine (tOPV) has been withdrawn and instead an inactivated poliovirus vaccine (IPV) and bivalent type 1 and type 3 OPV (bOPV) sequential immunization schedule has been implemented since 2016, but no immune persistence data are available for this polio vaccination strategy. This study aimed to assess immune persistence following different polio sequential immunization schedules. Venous blood was collected at 24, 36, and 48 months of age from participants who had completed sequential schedules of combined IPV and OPV in phase III clinical trials. The serum neutralizing antibody titers against poliovirus were determined, and the poliovirus-specific antibody-positive rates were evaluated. A total of 1104 participants were enrolled in this study. The positive rates of poliovirus type 1- and type 3-specific antibodies among the sequential immunization groups showed no significant difference at 24, 36, or 48 months of age. The positive rates of poliovirus type 2-specific antibody in the IPV-IPV-tOPV group at all time points were nearly 100%, which was significantly higher than the corresponding rates in other immunization groups (IPV-bOPV-bOPV and IPV-IPV-bOPV). Immunization schedules involving one or two doses of IPV followed by bOPV failed to maintain a high positive rate for poliovirus type 2-specific antibody.

The EG.5.1 variant of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been prevalent since mid-July 2023 in the United States and China. The variant BA.2.86 has become a major concern because it is 34 mutations away from the parental variant BA.2 and >30 mutations from XBB.1.5. There is an urgent need to evaluate whether the immunity of the population and current vaccines are protective against EG.5.1 and BA.2.86. Based on a cohort of two breakthrough-infected groups, the levels of neutralizing antibodies (NAbs) against different subvariants were measured using pseudovirus-based neutralization assays. XBB.1.5, EG.5.1, and BA.2.86 are comparably immune-evasive from neutralization by the plasma of individuals recovered from BA.5 infection (BA.5-convalescent) or XBB.1.9.2/XBB.1.5 infection following BA.5 infection (BA.5-XBB-convalescent). NAb levels against EG.5.1 and BA.2.86 subvariants remained >120 geometric mean titers (GMTs) in BA.5-XBB-convalescent individuals 2 months postinfection but were <40GMTs in BA.5-convalescent individuals. Furthermore, the XBB-targeting messenger RNA (mRNA) vaccine RQ3033 induced higher levels of NAbs against XBB.1.5, EG.5.1, and BA.2.86 than against BA.5-XBB infection. The results suggest that BA.2.86 and EG.5.1 are unlikely to cause more severe concerns than the currently circulating XBB subvariants and that the XBB.1.5-targeting mRNA vaccine tested has promising protection against EG.5.1 and BA.2.86.

Heterologous prime-boost has broken the protective immune response bottleneck of the COVID-19 vaccines. however, the underlying mechanisms have not been fully elucidated. Here, we investigated antibody responses and explored the response of germinal center (GC) to priming with inactivated vaccines and boosting with heterologous adenoviral-vectored vaccines or homologous inactivated vaccines in mice. Antibody responses were dramatically enhanced by both boosting regimens. Heterologous immunization induced more robust GC activation, characterized by increased Tfh cell populations and enhanced helper function. Additionally, increased B-cell activation and antibody production were observed in a heterologous regimen. Libra-seq was used to compare the differences of S1-, S2- and NTD-specific B cells between homologous and heterologous vaccination, respectively. S2-specific CD19+ B cells presented increased somatic hypermutations (SHMs), which were mainly enriched in plasma cells. Moreover, a heterologous booster dose promoted the clonal expansion of B cells specific to S2 and NTD regions. In conclusion, the functional role of Tfh and B cells following SARS-CoV-2 heterologous vaccination may be important for modulating antibody responses. These findings provide new insights for the development of SARS-CoV-2 vaccines that induce more robust antibody response.