Influence of previous Zika virus infection on acute dengue episode

IgA-driven neutrophil activation underlies post-Zika severe dengue disease in humans

The four dengue virus serotypes (DENV1-4) and the related Zika flavivirus (ZIKV) are major public health concerns worldwide. Primary immunity against ZIKV increases the risk of a subsequent severe DENV2 infection, presenting a significant challenge for developing safe and effective ZIKV vaccines. However, the mechanisms driving this phenomenon remain unclear. Leveraging our long-standing Pediatric Dengue Cohort Study in Nicaragua, we show that serum anti-NS1 IgA antibodies elicited after a primary ZIKV infection drive neutrophil activation and correlate with increased risk of subsequent severe DENV2 disease. Depletion experiments combined with ex vivo functional NETosis assays confirmed that anti-NS1 IgA antibodies drive neutrophil activation in dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Moreover, increased neutrophil degranulation in paired serum samples obtained during the acute DENV2 infection from the same individuals correlated with IgA binding to DENV2 NS1 and preceded the development of vascular leakage. This finding was corroborated in an orthogonal hospital-based study. Thus, serum anti-NS1 IgA enhances neutrophil activation in severe dengue, with implications for prognostics, therapeutics, and vaccines.

Serotype-specific epidemiological patterns of inapparent versus symptomatic primary dengue virus infections: a 17-year cohort study in Nicaragua

BACKGROUND

Dengue is the most prevalent mosquito-borne viral disease and a major public health problem worldwide. Most primary infections with the four dengue virus serotypes (DENV1-4) are inapparent; nonetheless, whether the distribution of symptomatic versus inapparent infections by serotype varies remains unknown. Here, we present (1) the evaluation of a DENV1-4 envelope domain III multiplex microsphere-based assay (EDIII-MMBA) to serotype inapparent primary infections and (2) its application leveraging 17 years of prospective sample collection from the Nicaraguan Pediatric Dengue Cohort Study (PDCS).

METHODS

We analysed primary DENV infections in the PDCS from 2004 to 2022 detected by inhibition ELISA (iELISA) or RT-PCR. First, we evaluated the performance of the EDIII-MMBA for serotyping with samples characterised by RT-PCR or focus reduction neutralisation test. Next, we analysed a subset of inapparent primary DENV infections in the PDCS with the EDIII-MMBA to evaluate the epidemiology of inapparent infections. Remaining infections were inferred using stochastic imputation, taking year and neighbourhood into account. Infection incidence and percentage of inapparent, symptomatic, and severe infections were analysed by serotype.

FINDINGS

Between Aug 30, 2004, and March 10, 2022, a total of 5931 DENV-naive participants were followed in the PDCS. There were 1626 primary infections (382 symptomatic, 1244 inapparent) detected by iELISA or RT-PCR over the study period. The EDIII-MMBA demonstrated excellent overall accuracy (100%, 95% CI 95·8-100) for serotyping inapparent primary DENV infections when evaluated against gold-standard serotyping methods. Of the 1244 inapparent infections, we analysed 574 (46%) using the EDIII-MMBA. We found that the majority of primary infections were inapparent, with DENV3 exhibiting the highest likelihood of symptomatic (pooled odds ratio compared with DENV1: 2·13, 95% CI 1·28-3·56) and severe (6·75, 2·01-22·62) primary infections, whereas DENV2 was similar to DENV1 in both analyses. Considerable within-year and between-year variation in serotype distribution between symptomatic and inapparent infections and circulation of serotypes undetected in symptomatic cases were observed in multiple years.

INTERPRETATION

Our study indicates that case surveillance skews the perceived epidemiological footprint of DENV. We reveal a more complex and intricate pattern of serotype distribution in inapparent infections. The substantial differences in infection outcomes by serotype emphasises the need for vaccines with balanced immunogenicity and efficacy across serotypes.

FUNDING

National Institute of Allergy and Infectious Diseases (National Institutes of Health) and Bill & Melinda Gates Foundation.

TRANSLATION

For the Spanish translation of the abstract see Supplementary Materials section.

Zika virus vaccines and monoclonal antibodies: a priority agenda for research and development

The 2015-16 Zika virus epidemic in the Americas drew global attention to Zika virus infection as a cause of microcephaly and Guillain-Barré syndrome. The epidemic highlighted the urgent need for preventive measures, including vaccines and monoclonal antibodies (mAbs). However, nearly 9 years later, no licensed Zika virus vaccines or mAbs are available, leaving the world's populations unprotected from ongoing disease transmission and future epidemics. The current low Zika virus incidence and unpredictability of future outbreaks complicates prospects for evaluation, licensure, and commercial viability of Zika virus vaccines and mAbs. We conducted an extensive review of Zika virus vaccines and mAbs in development, identifying 16 vaccines in phase 1 or phase 2 trials and three mAbs in phase 1 trials, and convened a 2-day meeting of 130 global Zika virus experts to discuss research priorities to advance their development. This Series paper summarises a priority research agenda to address key knowledge gaps and accelerate the licensure of Zika virus vaccines and mAbs for global use.

Development of nucleic acid-based vaccines against dengue and other mosquito-borne flaviviruses: the past, present, and future

Due to their widespread geographic distribution and frequent outbreaks, mosquito-borne flaviviruses, such as DENV (DENV), Zika virus (ZIKV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), and West Nile virus (WNV), are considered significant global public health threats and contribute to dramatic socioeconomic imbalances worldwide. The global prevalence of these viruses is largely driven by extensive international travels and ecological disruptions that create favorable conditions for the breeding of Aedes and Culex species, the mosquito vectors responsible for the spread of these pathogens. Currently, vaccines are available for only DENV, YFV, and JEV, but these face several challenges, including safety concerns, lengthy production processes, and logistical difficulties in distribution, especially in resource-limited regions, highlighting the urgent need for innovative vaccine approaches. Nucleic acid-based platforms, including DNA and mRNA vaccines, have emerged as promising alternatives due to their ability to elicit strong immune responses, facilitate rapid development, and support scalable manufacturing. This review provides a comprehensive update on the progress of DNA and mRNA vaccine development against mosquito-borne flaviviruses, detailing early efforts and current strategies that have produced candidates with remarkable protective efficacy and strong immunogenicity in preclinical models. Furthermore, we explore future directions for advancing nucleic acid vaccine candidates, which hold transformative potential for enhancing global public health.

Latin America's Dengue Outbreak Poses a Global Health Threat

Dengue fever, caused by the dengue virus (DENV), poses a significant global health challenge, particularly in tropical and subtropical regions. Recent increases in indigenous DENV cases in Europe are concerning, reflecting rising incidence linked to climate change and the spread of Aedes albopictus mosquitoes. These vectors thrive under environmental conditions like temperature and humidity, which are increasingly influenced by climate change. Additionally, global travel accelerates the cross-border spread of mosquito-borne diseases. DENV manifests clinically in a spectrum from asymptomatic cases to severe conditions like dengue hemorrhagic fever and dengue shock syndrome, influenced by viral serotype and host factors. In 2024, Brazil experienced a fourfold increase in dengue cases compared to 2023, accompanied by higher mortality. Conventional control measures, such as vector control, community engagement, and vaccination, proved insufficient as climate change exacerbated mosquito proliferation, challenging containment efforts. In this regard, our review analyzes prevention measures and therapeutic protocols during the outbreak while addressing DENV transmission dynamics, clinical presentations, and epidemiological shifts. It also evaluates diagnostic strategies combining clinical assessment with serological and molecular testing, providing information to improve diagnostic and preventive measures. The global expansion of dengue-endemic regions, including outbreaks in Europe, highlights the urgent need for enhanced surveillance, proactive interventions, and international collaboration to mitigate the growing threat of Dengue and other arboviruses like West Nile, Zika, Chikungunya, Oropouche, and Yellow Fever viruses.

Efficacy and safety of Butantan-DV in participants aged 2-59 years through an extended follow-up: results from a double-blind, randomised, placebo-controlled, phase 3, multicentre trial in Brazil

BACKGROUND

A single-dose dengue vaccine that protects individuals across a wide age range and regardless of dengue serostatus is an unmet need. We assessed the safety and efficacy of the live, attenuated, tetravalent Butantan-dengue vaccine (Butantan-DV) in adults, adolescents, and children. We previously reported the primary and secondary efficacy and safety endpoints in the initial 2 years of follow-up. Here we report the results through an extended follow-up period, with an average of 3·7 years of follow-up.

METHODS

In this double-blind, randomised, placebo-controlled, phase 3, multicentre trial in Brazil, healthy participants (aged 2-59 years) who had not previously received a dengue vaccine were enrolled and randomly assigned 2:1 (stratified by age 18-59 years, 7-17 years, and 2-6 years) using a central electronic randomisation system to receive 0·5 mL of Butantan-DV (containing approximately 103 plaque-forming units of each of the four vaccine virus strains) or placebo, administered subcutaneously. Syringes containing vaccine or placebo were prepared by an unmasked trial pharmacist who was not involved in any subsequent participant assessments; other site staff and the participants remained unaware of the group allocations. Vaccine efficacy was calculated with the accrual of virologically confirmed dengue (VCD) cases (by RT-PCR) at least 28 days after vaccination up until the cutoff (at least 2 years of follow-up from the last participant enrolled). The primary endpoint was vaccine efficacy against VCD after day 28 by any dengue virus (DENV) serotype regardless of dengue serostatus at baseline in the per-protocol population. The primary and secondary safety endpoints up until day 21 were previously reported; secondary safety endpoints include the frequency of unsolicited vaccine-related adverse events after day 22. Safety analyses were done on all participants as treated. This trial is registered with ClinicalTrials.gov (NCT02406729) and is ongoing.

FINDINGS

Of 16 363 participants assessed for eligibility, 16 235 were randomly assigned between Feb 22, 2016, and July 5, 2019, and received single-dose Butantan-DV (10 259 participants) or placebo (5976 participants). 16 162 participants (Butantan-DV n=10 215; placebo n=5947) were included in the per-protocol population and 16 235 (Butantan-DV n=10 259; placebo n=5976) in the safety population. At the data cutoff (July 13, 2021), participants had 2-5 years of follow-up (mean 3·7 years [SD 1·0], median 4·0 years [IQR 3·2-4·5]). 356 VCD cases were captured through the follow-up (128 in the vaccine group and 228 in the placebo group). Vaccine efficacy against VCD caused by any DENV serotype was 67·3% (95% CI 59·4-73·9); cases caused by DENV-3 or DENV-4 were not observed. The proportions of participants who had serious adverse events were similar between treatment groups (637 [6·2%] in the vaccine group and 395 [6·6%] in the placebo group) up until the cutoff.

INTERPRETATION

A single dose of Butantan-DV was generally well tolerated and efficacious against symptomatic VCD (caused by DENV-1 and DENV-2) for a mean of 3·7 years. These findings support the continued development of Butantan-DV to prevent dengue disease in children, adolescents, and adults regardless of dengue serostatus.

FUNDING

Instituto Butantan and Merck Sharp & Dohme LLC, a subsidiary of Merck & Co.

TRANSLATIONS

For the Spanish and Portuguese translations of the abstract see Supplementary Materials section.

Modelling the mechanisms of antibody mixtures in viral infections: the cases of sequential homologous and heterologous dengue infections

Antibodies play an essential role in the immune response to viral infections, vaccination or antibody therapy. Nevertheless, they can be either protective or harmful during the immune response. Moreover, competition or cooperation between mixed antibodies can enhance or reduce this protective or harmful effect. Using the laws of chemical reactions, we propose a new approach to modelling the antigen-antibody complex activity. The resulting expression covers not only purely competitive or purely independent binding but also synergistic binding which, depending on the antibodies, can promote either neutralization or enhancement of viral activity. We then integrate this expression of viral activity in a within-host model and investigate the existence of steady-states and their asymptotic stability. We complete our study with numerical simulations to illustrate different scenarios: firstly, where both antibodies are neutralizing and secondly, where one antibody is neutralizing and the other enhancing. The results indicate that efficient viral neutralization is associated with purely independent antibody binding, whereas strong viral activity enhancement is expected in the case of purely competitive antibody binding. Finally, data collected during a secondary dengue infection were used to validate the model. The dataset includes sequential measurements of virus and antibody titres during viremia in patients. Data fitting shows that the two antibodies are in strong competition, as the synergistic binding is low. This contributes to the high levels of virus titres and may explain the antibody-dependent enhancement phenomenon. Besides, the mortality of infected cells is almost twice as high as that of susceptible cells, and the heterogeneity of viral kinetics in patients is associated with variability in antibody responses between individuals. Other applications of the model may be considered, such as the efficacy of vaccines and antibody-based therapies.

The Risk of Virus Emergence in South America: A Subtle Balance Between Increasingly Favorable Conditions and a Protective Environment

South American ecosystems host astonishing biodiversity, with potentially great richness in viruses. However, these ecosystems have not yet been the source of any widespread, epidemic viruses. Here we explore a set of putative causes that may explain this apparent paradox. We discuss that human presence in South America is recent, beginning around 14,000 years ago; that few domestications of native species have occurred; and that successive immigration events associated with Old World virus introductions reduced the likelihood of spillovers and adaptation of local viruses into humans. Also, the diversity and ecological characteristics of vertebrate hosts might serve as protective factors. Moreover, although forest areas remained well preserved until recently, current brutal, sudden, and large-scale clear cuts through the forest have resulted in nearly no ecotones, which are essential for creating an adaptive gradient of microbes, hosts, and vectors. This may be temporarily preventing virus emergence. Nevertheless, the mid-term effect of such drastic changes in habitats and landscapes, coupled with explosive urbanization and climate changes, must not be overlooked by health authorities.

Dengue hospitalizations and in-hospital mortality changes in trend in Ecuador: a nationwide study from 2015 to 2022

OBJECTIVE

This study aimed to analyze dengue hospitalizations and in-hospital mortality trends in Ecuador, along with sociodemographic factors influencing adverse outcomes.

METHODS

This study included 31,616 dengue hospitalizations in Ecuador during 2015-2022, of which 115 (0.36%) died. Data were extracted from national hospital registries. Age adjusted rates were calculated, and for the analysis of changes in trend, a Joinpoint regression was performed. Multivariate binary and multinomial logistic regressions were performed for assessing sociodemographic factors influencing dengue adverse outcomes.

RESULTS

During 2015-2022, the mean age adjusted dengue hospitalization rate was 22.3 per 100,000 inhabitants with 49.41% annual decrease during 2015-2017 and 31.73% annual increase during 2017-2022 with higher rates in 2020 with 31.61, 2021 with 34.42, and 2022 with 25.81. The mean dengue in-hospital mortality rate was 0.08, mortality rates did not show significant changes during 2015-2022. Higher probability of death was observed in ages ≥50 years and ethnic minorities. People living in rural areas exhibited a 64% higher risk for complicated dengue hospitalization.

CONCLUSIONS

It was observed as an important accomplishment in Ecuador's ongoing efforts to improve healthcare regarding dengue. 0.36% of dengue hospitalizations ended in death which is below the recommended 1%. The increase in dengue hospitalizations in Ecuador during recent years remains a concern. The COVID-19 pandemic might have influenced dengue prevention and vector control to be neglected leading to an increase in cases.

Serotype-Specific Epidemiological Patterns of Inapparent versus Symptomatic Primary Dengue Virus Infections: A 17-year cohort study in Nicaragua

Dengue is the most prevalent mosquito-borne viral disease and a major public health problem worldwide. Most primary infections with the four dengue virus serotypes (DENV1-4) are inapparent; nonetheless, whether the distribution of symptomatic versus inapparent infections by serotype varies remains unknown. Here, we present (1) the evaluation of a multiplex DENV1-4 envelope domain III multiplex microsphere-based assay (EDIII-MMBA) to serotype inapparent primary infections and (2) its application leveraging 17 years of prospective sample collection from the Nicaraguan Pediatric Dengue Cohort Study (PDCS). First, we evaluated the performance of the EDIII-MMBA with samples characterized by RT-PCR or focus reduction neutralization test. Next, we analyzed 46% (N=574) of total inapparent primary DENV infections in the PDCS with the EDIII-MMBA to evaluate the epidemiology of inapparent infections. Remaining infections were inferred using stochastic imputation, taking year and neighborhood into account. Infection incidence and percentage of inapparent, symptomatic, and severe infections were analyzed by serotype. The EDIII-MMBA demonstrated excellent overall accuracy (100%, 95.8-100%) for serotyping symptomatic and inapparent primary DENV infections when evaluated against gold-standard serotyping methods. We found that a significant majority of primary infections were inapparent, with DENV3 exhibiting the highest likelihood of symptomatic and severe primary infections (Pooled OR compared to DENV1 = 2.13, 95% CI 1.28-3.56, and 6.75, 2.01-22.62, respectively), whereas DENV2 was similar to DENV1 in both analyses. Significant within- and between-year variation in serotype distribution between symptomatic and inapparent infections and circulation of serotypes undetected in symptomatic cases were observed in multiple years. Our study indicates that case surveillance skews the perceived epidemiological footprint of DENV. We reveal a more complex and intricate pattern of serotype distribution in inapparent infections. The significant differences in infection outcomes by serotype emphasizes the need for vaccines with balanced immunogenicity and efficacy across serotypes.

Molecular surveillance for dengue serotypes among the population living in Moyen-Ogooué province, Gabon; evidence of the presence of dengue serotype 1

BACKGROUND

Despite dengue virus (DENV) outbreak in Gabon a decade ago, less is known on the potential circulation of DENV serotypes in the country. Previous studies conducted in some areas of the country, are limited to hospital-based surveys which reported the presence of some cases of serotype 2 and 3 seven years ago and more recently the serotype 1. As further investigation, we extend the survey to the community of Moyen Ogooué region with the aim to assess the presence of the dengue virus serotypes, additionally to characterize chikungunya (CHIKV) infection and describe the symptomatology associated with infections.

METHOD

A cross-sectional survey was conducted from April 2020 to March 2021. The study included participants of both sexes and any age one year and above, with fever or history of fever in the past seven days until blood collection. Eligible volunteers were clinically examined, and blood sample was collected for the detection of DENV and CHIKV using RT-qPCR. Positive samples were selected for the target sequencing.

RESULTS

A total of 579 volunteers were included. Their mean age (SD) was 20 (20) years with 55% of them being female. Four cases of DENV infection were diagnosed giving a prevalence of 0.7% (95%CI: 0.2-1.8) in our cohort while no case of CHIKV was detected. The common symptoms and signs presented by the DENV cases included fatigue, arthralgia myalgia, cough, and loss of appetite. DENV-1was the only virus detected by RT-qPCR.

CONCLUSION

Our results confirm the presence of active dengue infection in the region, particularly DENV-1, and could suggest the decline of DENV-2 and DENV-3. Continuous surveillance remains paramount to comprehensively describe the extent of dengue serotypes distribution in the Moyen-Ogooué region of Gabon.

Primary exposure to Zika virus is linked with increased risk of symptomatic dengue virus infection with serotypes 2, 3, and 4, but not 1

Infection with any of the four dengue virus serotypes (DENV1-4) can protect against or enhance subsequent dengue depending on preexisting antibodies and infecting serotype. Additionally, primary infection with the related flavivirus Zika virus (ZIKV) is associated with increased risk of DENV2 disease. Here, we measured how prior DENV and ZIKV immunity influenced risk of disease caused by DENV1-4 in a pediatric Nicaraguan cohort. Of 3412 participants in 2022, 10.6% experienced dengue cases caused by DENV1 (n = 139), DENV4 (n = 133), DENV3 (n = 54), DENV2 (n = 9), or an undetermined serotype (n = 39). Longitudinal clinical and serological data were used to define infection histories, and generalized linear and additive models adjusted for age, sex, time since last infection, and year, and repeat measurements were used to predict disease risk. Compared with flavivirus-naïve participants, primary ZIKV infection was associated with increased risk of disease caused by DENV4 (relative risk = 2.62, 95% confidence interval: 1.48 to 4.63) and DENV3 (2.90, 1.34 to 6.27), but not DENV1 infection. Primary DENV infection or DENV followed by ZIKV infection was also associated with increased risk of DENV4 disease. We reanalyzed 19 years of cohort data and demonstrated that prior flavivirus immunity and antibody titer had distinct associations with disease risk depending on incoming serotype. We thus find that prior ZIKV infection, like prior DENV infection, is associated with increased risk of disease with certain DENV serotypes. Cross-reactivity among flaviviruses should be considered when assessing vaccine safety and efficacy.

Diabetes as risk factor to severity of dengue in naïve patients

Background

Dengue cases can progress to severe ant life-threating forms particularly in subsequent heterologous infections. However, recent studies had explored additional risk factors, including underlying health conditions, even in individuals without prior exposure to dengue, notably, in patients with endothelial dysfunction and chronic inflammation. This study examines the link between diabetes and the development of severe dengue disease in dengue-naive patients during the 2019 dengue outbreak in São Jose do Rio Preto, Brazil.

Methodology

We enrolled 529 laboratory-confirmed dengue cases, identified through DENV RT-PCR or NS1 antigen assays in a hospital cohort of acute febrile illness. Subsequently, we investigated the presence of anti-dengue and anti-Zika IgG antibodies. Samples testing positive for Zika were excluded from the analyses. Two groups were analyzed: naïve (DV-), and dengue history (DV+).

Results

Initially, presence of diabetes and kidney disease, as well as being dengue-naive, were associated with a higher frequency of severe and potentially severe clinical outcomes. Multivariate analysis identified diabetes as a risk factor, while the presence of anti-dengue antibodies was considered protective. Analysis of dengue naïve samples, highlighted diabetes as an independent risk factor to severe forms of dengue disease. In DV+ patients, no condition was highlighted as a risk factor by univariate analysis or multivariate analysis.

Conclusions

We investigated and confirmed diabetes as a risk factor for severe dengue disease in individuals without prior dengue or Zika exposure. Our conclusions raise significant concerns given diabetes' ever increasing global prevalence and its potential impact on patients with or previous dengue exposure.

Primary exposure to Zika virus increases risk of symptomatic dengue virus infection with serotypes 2, 3, and 4 but not serotype 1

Infection with any of the four dengue virus serotypes (DENV1-4) can protect against or enhance subsequent dengue depending on pre-existing antibodies and the subsequent infecting serotype. Additionally, primary infection with the related flavivirus Zika virus (ZIKV) has been shown to increase DENV2 disease. Here, we measured how prior DENV and ZIKV immunity influenced risk of disease caused by all four serotypes in a pediatric Nicaraguan cohort. Of 3,412 participants in 2022, 10.6% experienced symptomatic DENV infections caused by DENV1 (n=139), DENV4 (n=133), DENV3 (n=54), DENV2 (n=9), or an undetermined serotype (n=39). Longitudinal clinical and serological data were used to define infection histories, and generalized linear and additive models adjusted for age, sex, time since the last infection, cohort year, and repeat measurements were used to predict disease risk. Compared to flavivirus-naïve participants, primary ZIKV infection increased disease risk of DENV4 (relative risk = 2.62, 95% confidence interval: 1.48-4.63) and DENV3 (2.90, 1.34-6.27) but not DENV1 (1.20, 0.72-1.99). Primary DENV infection or a DENV followed by ZIKV infection also increased DENV4 risk. We re-analyzed 19 years of cohort data and demonstrated that prior flavivirus-immunity and pre-existing antibody titer differentially affected disease risk for incoming serotypes, increasing risk of DENV2 and DENV4, protecting against DENV1, and protecting at high titers but enhancing at low titers against DENV3. We thus find that prior ZIKV infection, like prior DENV infection, increases risk of certain DENV serotypes. Cross-reactivity among flaviviruses should be carefully considered when assessing vaccine safety and efficacy.