Background/Objectives: Given the overlapping seasonality of influenza (Flu) and respiratory syncytial virus (RSV) infections in human populations, Flu–RSV combination vaccines are urgently needed. However, development of combo-vaccines is often faced with intra-vaccine interference which could compromise vaccination outcomes. Here we present an approach to overcoming this problem using a microneedle array patch (MAP)-based combo-vaccine with minimum intra-vaccine interference. Methods: Vaccine-laden dissolving MAPs were fabricated using a two-step micro-molding process with polyvinyl alcohol as major excipient. A partition-loading strategy was adopted to ensure spatially segregated distribution of a split-virus Flu vaccine and recombinant prefusion protein of RSV in separate MAP sectors. Serum samples from BALB/c mice post-vaccination were assessed for titers of binding and neutralizing antibodies against the viruses. Live virus challenge studies were carried out to assess the protection efficacy of the MAP-based vaccines. Results: Although i.m. administered standalone Flu and RSV vaccines were able to induce strong IgG responses in BALB/c mice, bidirectional intra-vaccine interference was observed when the two vaccines were co-administered in premixed form. However, when the two vaccines were loaded onto nonoverlapping sectors of D-MAPs for intradermal vaccination, the intra-vaccine interference effect was effectively overcome. The partition-loaded MAP-Flu/RSV combo-vaccine elicited antigen-specific IgG with robust virus-neutralizing activity and was strongly efficacious against either virus in challenge studies. Conclusions: Our data provide proof-of-concept evidence for the potential usefulness of partition-loaded MAPs in overcoming a critical barrier in vaccinology and offer a promising platform for future clinical translation.

Rabies is an acute and fatal zoonotic disease caused by the rabies virus, responsible for approximately 59,000 deaths worldwide each year. Once clinical symptoms manifest, the case fatality rate approaches 100%. Vaccination remains the only effective strategy for prevention and control. Currently, human rabies vaccines approved by regulatory authorities such as the U.S. Food and Drug Administration (FDA), and the China National Medical Products Administration (NMPA) are all inactivated, adjuvant-free formulations. These vaccines are associated with several limitations, including weak immunogenicity, delayed induction of neutralizing antibodies, complex immunization schedules, and poor patient compliance. Adjuvants, as nonspecific immunoenhancers, can potentiate the immune response even at low antigen doses and reduce the number of required doses, offering a promising approach to overcome the aforementioned challenges. This article reviews recent advances in adjuvants suitable for rabies vaccines and discusses the key challenges currently faced in the development of adjuvanted rabies vaccines.

To address the limitations of egg-based influenza vaccine production, serum-free suspension culture of Madin-Darby Canine Kidney cells (MDCK) has emerged as a promising alternative. In this study, a quadrivalent influenza virus subunit vaccine was developed using this platform by culturing four viral strains, followed by purification, inactivation, and formulation. Preclinical safety evaluations in rats, rabbits, and guinea pigs demonstrated no systemic toxicity. In mice, immunization with the vaccine elicited significant hemagglutination inhibition and microneutralization antibodies against H1N1, H3N2, BY, and BV strains at 28 and 42 days post-vaccination. These results indicate that the vaccine candidate possesses a favorable safety profile and induces robust immunogenicity.

Developing universal influenza vaccines (UIVs) capable of eliciting broad protection remains a critical public health priority. Neuraminidase (NA), a relatively conserved surface antigen of influenza viruses, is a promising target for UIV design. Here, we produced full-length trivalent NA proteins via a baculovirus-insect cell expression system, matching the WHO-recommended strains (H1N1, H3N2, and B/Victoria) for the 2024–2025 season. Immunogenicity evaluation of N2NA (derived from H3N2) in mice demonstrated that nanoemulsion (NE) adjuvant significantly enhanced NA-inhibiting (NI) antibody titers, CD4 T cell responses, and the numbers of IL-2-, IL-4- and IFN-γ-secreting lymphocytes compared to the unadjuvanted vaccine. Monovalent N1 NA and BV NA with NE adjuvant similarly induced stronger NI antibody responses and antiviral protection. Furthermore, the NE-adjuvanted trivalent NA vaccine (N1+N2+BV) elicited robust humoral and cellular immunity and provided effective protection in mice against two H1N1, two B/Victoria, and one H5N1 strain. Collectively, these findings support the efficacy of a multivalent NA-based vaccine strategy and highlight its strong potential as a candidate UIV.

Objective: To evaluate the immunogenicity and safety of trivalent inactivated influenza vaccine (IIV3) in adults aged ≥18 years living with HIV and to provide evidence supporting influenza vaccination in this population in China. Methods: This single-center, open-label comparative analysis was derived from a larger three-arm clinical study. For the present comparative analysis, 472 vaccinated participants were planned, including 236 adults living with HIV (Group 1) and 236 age- and sex-comparable HIV-uninfected adults (Group 2). Participants in both groups received one dose of IIV3 (0.5 mL) on Day 0. Blood samples were collected before and 28 days after vaccination for hemagglutination inhibition (HI) antibody testing against A(H1N1), A(H3N2), and B/Victoria strains. Immunogenicity endpoints included seroconversion rate, seroprotection rate, geometric mean titer (GMT), and geometric mean increase (GMI). Safety was assessed by monitoring solicited and unsolicited adverse events (AEs) and serious adverse events (SAEs) during 6 months of follow-up. An unvaccinated cohort of adults living with HIV from the original trial was included only for an exploratory, descriptive analysis of influenza-like illness (ILI), without assessment of vaccine efficacy. Results: A total of 489 participants were enrolled, including 237 in Group 1 and 252 in Group 2. At 28 days post-vaccination, seroconversion rates did not differ significantly between Group 1 and Group 2 for A(H1N1) (91.00% vs. 86.69%, P > 0.05), but significantly lower for A(H3N2) (49.50% vs. 89.52%) and B/Victoria (40.00% vs. 64.52%) (both P < 0.001). Seroprotection rates were also lower in Group 1 than in Group 2 for A(H1N1), A(H3N2), and B/Victoria (94.00% vs. 97.98%, 63.50% vs. 97.18%, and 40.50% vs. 68.55%, respectively). Post-vaccination GMTs were significantly lower in Group 1 for all three strains (all P < 0.001). GMI was higher for A(H1N1) but lower for A(H3N2) and B/Victoria in Group 1 than in Group 2 (all P < 0.001). Multivariable analyses showed that HIV infection remained independently associated with several measures of vaccine-induced immune responses after adjustment for demographic and clinical factors, particularly for A(H3N2). IIV3 was generally safe and well tolerated. Most AEs were mild in severity, and no Grade 4 adverse reactions or vaccine-related SAEs were reported. During the period from 29 days to 6 months after vaccination, few influenza-like illness events were reported among vaccinated and unvaccinated participants living with HIV; these findings were descriptive and were not used to assess vaccine efficacy against influenza. Conclusion: Adults living with HIV developed substantial antibody responses following IIV3 vaccination, although the magnitude of response varied across influenza strains. A(H1N1) seroconversion was high in adults living with HIV, whereas responses to A(H3N2) and B/Victoria were generally lower than those in HIV-uninfected adults. HIV infection remained associated with reduced vaccine-induced immune responses for several strain-specific outcomes after multivariable adjustment, with associations particularly evident for A(H3N2). IIV3 was safe and well tolerated, supporting current recommendations for influenza vaccination in adults living with HIV. Clinical trial registration: https://www.chictr.org.cn/showprojEN.html?proj=255613 , identifier ChiCTR2500112191.