Aravinda M. de Silva

Background: Dengvaxia® was the first live attenuated tetravalent dengue virus (DENV) vaccine to be tested and approved for use in people. While Dengvaxia® was designed to be tetravalent, in humans, the vaccine performed like a monovalent DENV4 vaccine because the DENV4 vaccine virus replicated better than other vaccine serotypes. Dengvaxia® was safe and efficacious in children who were DENV-immune at baseline (BL) and contraindicated for use in DENV-naive children. Methods: When Dengvaxia® was rolled out as a pediatric vaccine in the Philippines in 2016, we established a prospective cohort to assess vaccine performance by BL dengue serostatus. Here, we report on how BL monotypic immunity to each serotype (reflecting one past DENV infection) impacted Dengvaxia® responses. Results: We observed that in children with BL immunity to DENV1, 2, or 3, the vaccine stimulated a secondary serotype cross-neutralizing Ab response, which likely explains the overall favorable performance of the vaccine in seropositive children enrolled in phase 3 trials. We observed a high frequency (61%) of vaccine suppression among DENV4 monotypic immune children. Conclusions: Our results confirm the replication dominance of the DENV4 vaccine component in Dengvaxia® and directly implicate pre-existing DENV4 immunity in the suppression of the vaccine. Our results have broader implications for evaluating the performance of other DENV vaccines in seropositive individuals.

Dengue is the canonical viral disease for which immune history is a determinant of protective versus pathogenic responses and immunogenicity. Yet, because of limitations in animal models and clinical presentation after peak viremia, how preinfection and early immune responses affect dengue outcome is not confirmed. We conducted a phase 1 clinical trial with 45 healthy adults to test whether secondary infection challenge with a heterotypic, full-length, attenuated virus increases viremia and immunogenicity compared with primary and tertiary infection. Viremia was associated with more, but still mild, clinical signs and symptoms, and secondary infection resulted in greater viremia, neutralizing antibodies, and protective T cell responses. However, those whose baseline antibodies most efficiently increased dengue virus replication in an in vitro assay experienced delayed inflammatory and adaptive immune activation, the highest viremia, strong acute immune responses, and waning of potent CD8 ⁺ T cells and antibodies. In contrast, higher baseline antibodies against the nonstructural protein 1 of multiple serotypes predicted early interferon and balanced immune activation, viremia control, and development of enduring, potent B and T cells, revealing how vaccines can induce broad, long-lasting protection. Last, individuals with potent and neutralizing antibodies and IFN-γ ⁺ T cells at baseline experienced minimal viral replication. Together, these findings demonstrate that controlled human challenge with dengue virus can delineate coordinated versus dysregulated acute immune responses and their effects on immunogenicity, informing therapeutic and vaccine strategies for dengue and other viral diseases.

Dengue has emerged as the leading mosquito-borne viral threat in the Americas, with over 13 million cases reported in 2024 alone. This review synthesizes current knowledge on dengue virus biology, epidemiology, and discusses the benefits of a coordinated regional elimination strategy in Latin America. Genetic diversity across the four dengue virus serotypes influences circulation patterns and disease severity. We describe virion structure and host cell interactions and the human immune response, including properties of antibodies correlated with protection and antibody-enhanced severe infections. Surveillance data from the Americas reveal exponential case growth and increasing healthcare costs. Current prevention strategies — two new vaccines and biological vector control including Wolbachia replacement — offer tools not available a decade ago. However, insecticide resistance has rendered conventional chemical control ineffective. Latin America, with established regional coordinating bodies, sustained government commitment and institutional infrastructure, may be uniquely positioned to move from disease control to elimination through a phased, evidence-based regional strategy integrating vaccination, novel vector control strategies, and strengthened clinical management in priority high-burden areas.

Dengue virus (DENV) vaccines should be designed to induce balanced protective immunity to all 4 DENV serotypes to mitigate the risk of vaccine-enhanced dengue disease. The first tetravalent live DENV vaccine (Dengvaxia) tested in humans was efficacious in children who were partially immune to DENV at baseline. In DENV-naive children, the vaccine was not efficacious and placed some children at risk of more severe WT DENV breakthrough infections. To define dengue vaccine responses at the individual patient level and their relationship to mild and severe dengue infections, we prospectively studied a cohort of DENV-naive children who received 1 dose of Dengvaxia. The vaccine stimulated variable responses that neutralized 0, 1 (monotypic), or 2+ (multitypic) serotypes in individual children. Using a logistic regression model, we found that vaccinated children with neutralizing antibody (NAb) to 1 serotype only were at greater risk developing dengue compared with children who were not vaccinated (odds ratio 5.07). This risk was not observed in vaccinated children with no NAb or NAb to 2 or more serotypes. We propose that individuals with durable NAb to 1 serotype have an abundance of serotype cross-reactive, nonneutralizing antibodies implicated in the enhanced replication of heterologous serotypes.

Zika virus (ZIKV), a flavivirus, causes a range of clinical complications including microcephaly in human fetuses. Currently, there is no treatment or vaccine. Different maturation states (mature and immature forms) of flavivirus particles have been observed to be released from infected cells and are infectious. To understand how an ultrapotent human antibody (HMAb) A9E can neutralize these Zika particles, we determined the cryoEM structures of the A9E Fab fragment complexed with mature (mZIKV) and immature (immZIKV) ZIKV to 2.8Å and 7.5Å, respectively. A9E binds to an epitope spanning Domain I (EDI), EDIII, and their linker in an E protein protomer in both immZIKV and mZIKV particles. A9E generally inhibited prior to or during virus attachment to cells, via virus aggregation, distortion of virus particles and inhibition of receptor binding. ImmZIKV is particularly sensitive to structural distortion by Fab A9E. The primary mode of infection used by ImmZIKV is via antibody-dependent enhancement of infection (ADE)—the formation of virus complex with nonneutralizing or subneutralizing concentrations of antibodies, that leads to enhanced infection of Fcγ positive myeloid cells. IgG A9E, by itself displays poor ADE activity. When IgG LALA mutant or Fab A9E is added to other enhancing antibody (DV62.5):virus complexes, they can strongly reduce the overall ADE activity. This is likely due to their ability to distort virus particle structure, suggesting that HMAb A9E could be a potential prophylactic and therapeutic candidate against all maturation states of ZIKV.

Background: Understanding the immune mechanisms that differentiate protective from pathogenic responses during dengue virus (DENV) infection is critical for effective vaccine development. Objective: To investigate how CD4⁺ T cell depletion alters viral control and the humoral immune response during primary DENV2 infection in a non-human primate (NHP) model. Methods: Rhesus macaques were depleted of CD4⁺ T cells prior to DENV2 infection. Viral kinetics, B cell activation, antibody specificity, and functional outcomes were evaluated longitudinally, including cross-reactivity and antibody-dependent enhancement (ADE) potential. Results: CD4⁺ T cells were essential for early viral clearance and the generation of robust, type-specific neutralizing antibodies. In their absence, animals exhibited early non-specific polyclonal B cell activation, delayed isotype switching, and an expanded repertoire of cross-reactive antibodies to DENV and Zika virus (ZIKV), with diminished neutralizing capacity. CD4-depleted macaques also showed increased ADE potential, particularly against ZIKV, and elevated anti-NS1 IgG titers that persisted one-year post-infection. Conclusion: CD4⁺ T cells play a critical role in orchestrating effective, durable, and type-specific antibody responses during primary DENV infection. Their absence leads to delayed antibody maturation, greater cross-reactivity, and higher ADE potential. These findings emphasize the need for DENV and ZIKV vaccines to include CD4⁺ T cell epitopes that promote high-quality, type-specific antibody responses and minimize ADE risk.

Historically, DENV-4 has been rarely associated with epidemics and has been less well-studied than DENV-1 to -3. Epidemic dengue struck several South and Central American countries in 2022, with Nicaragua reporting the highest incidence. In an acute febrile illness (AFI) cohort enrolled from June to September 2022, 58 (34%) of 172 patients had PCR-confirmed dengue, of which 46 (79%) were serotyped as DENV-4. In this cohort, acute dengue, as a proportion of AFI, increased from 8% in June to a peak of 58% in August. Genome sequencing and phylogenetic analysis identified a lineage of DENV-4 Genotype IIb (GIIb) with six amino acid substitutions on the surface-exposed regions of the envelope (E) protein as compared to a reference sequence from 2005. Indeed, two of these mutations appear to be novel and located at G172E or near N174K, an antigenic epitope on domain I. Most (90%, 43/48) DENV-4 patients had pre-existing DENV IgG (secondary dengue), at the acute phase. Secondary dengue was associated with the male sex (prevalence ratio (PR)), 6.88) and being younger than 11 years of age (PR, 8.38). Further analysis showed no association between past Zika exposure and DENV-4 acute illness in older subjects (≥12 years of age). In conclusion, our study describes an epidemic of DENV-4 in León, Nicaragua, associated with a novel lineage of genotype GIIb, which contains two amino acid changes not observed in DENV-4 before 2022.

Background: Understanding the immune mechanisms that differentiate protective from pathogenic responses during dengue virus (DENV) infection is critical for effective vaccine development. Objective: To investigate how CD4+ T cell depletion alters viral control and the humoral immune response during primary DENV2 infection in a non-human primate (NHP) model. Methods: Rhesus macaques were depleted of CD4+ T cells prior to DENV2 infection. Viral kinetics, B cell activation, antibody specificity, and functional outcomes were evaluated longitudinally, including cross-reactivity and antibody-dependent enhancement (ADE) potential. Results: CD4+ T cells were essential for early viral clearance and the generation of robust, type-specific neutralizing antibodies. In their absence, animals exhibited early polyclonal B cell activation, delayed isotype switching, and an expanded repertoire of cross-reactive antibodies to DENV and Zika virus (ZIKV), with diminished neutralizing capacity. CD4-depleted macaques also showed increased ADE potential, particularly against ZIKV, and elevated anti-NS1 IgG titers that persisted one-year post-infection. Conclusion: CD4+ T cells play a critical role in orchestrating effective, durable, and type-specific antibody responses during primary DENV infection. Their absence leads to delayed antibody maturation, greater cross-reactivity, and higher ADE potential. These findings emphasize the need for dengue and Zika vaccines to include CD4+ T cell epitopes that promote high-quality, type-specific antibody responses and minimize ADE risk.

Cross-reactive antibodies to epitopes that span envelope proteins on the virion surface are hypothesized to protect against dengue virus (DENV) infection and disease. Here, we measured antibodies targeting a quaternary epitope called the envelope dimer epitope (EDE) as well as neutralizing and binding antibodies and evaluated their association with DENV infection, vaccine response, and disease outcome in dengue-vaccinated ( n = 164) and dengue-unvaccinated children ( n = 88) within a longitudinal cohort in Cebu, Philippines ( n = 2996). Antibodies targeting EDE were prevalent and associated with broad neutralization of mature DENV1 to DENV4 virions in those with evidence of at least two prior DENV infections but were mostly absent in those with only one prior infection. Subsequent infection and vaccination boosted titers of EDE-like antibodies, neutralizing antibodies, and DENV-binding antibodies. EDE-like antibodies were associated with reduced risk of symptomatic dengue and more severe dengue and statistically explained the protective effect of binding and neutralizing antibodies on dengue. Thus, antibodies targeting quaternary epitopes help explain the broad cross-protection observed in those with multiple prior DENV exposures, making them useful for evaluation and development of future vaccines and therapeutics.

The four serotypes of dengue virus (DENV1-4) are a major health concern putting 50% of the global population at risk of infection. Crucially, DENV vaccines must be tetravalent to provide protection against all four serotypes because immunity to only one serotype can enhance infections caused by heterologous serotypes. Uneven replication of live-attenuated viruses in tetravalent vaccines can lead to disease enhancement instead of protection. Subunit vaccines are a promising alternative as the vaccine components are not dependent on viral replication and antigen doses can be controlled to achieve a balanced response. Here, we show that a tetravalent subunit vaccine of dengue envelope (E) proteins computationally stabilized to form native-like dimers elicits type-specific neutralizing antibodies in mice against all four serotypes. The immune response was enhanced by displaying the E dimers on liposomes embedded with adjuvant, and no interference was detected between the four components.