Dengue seroprevalence data are useful for understanding epidemiologic trends and transmission dynamics, and for making decisions about implementation of dengue control programs. A logistical challenge to seroprevalence surveys is the collection and transport of serum samples. For conducting large and repeated dengue serosurveys, dried blood spots (DBS) would allow easier sample collection, shipment, transport, and storage than standard serum collection methods. Further evidence is needed to understand how well DBS performs compared with standard serum collection methods in laboratory assays. We evaluated the detection of anti-dengue antibodies by IgG indirect ELISA when using DBS compared with sera. Specimens were collected from healthy children in Cebu, Philippines, who would be 9–14 years of age at the time of a mass dengue vaccination program. Using an ELISA index value cutoff of 0.9, 1,285/1,488 (86.4%) of the DBS were seropositive and 203 (13.6%) were seronegative, compared with 1,292/1,488 (86.8%) seropositive and 196 (13.2%) seronegative serum samples. Compared with sera, the DBS method had a 98.3% sensitivity, 92.4% specificity, 98.9% positive predictive value, and 89.2% negative predictive value. Considering the advantages in terms of sample collection, shipment, and storage, DBS sampling may be appropriate for dengue population serosurveys.

The standard dengue virus (DENV) neutralization assay inconsistently predicts dengue protection. We compare how IgG ELISA, envelope domain III (EDIII), or non-structural protein 1 (NS1) binding antibodies, and titers from plaque reduction neutralization tests (PRNTs) using standard and mature viruses are associated with dengue. The ELISA measures IgG antibodies that bind to inactivated DENV1-4. The EDIII and NS1 assays measure binding antibodies, and the PRNTs measure neutralizing antibodies to each specific DENV serotype. Healthy children (n = 1206) in Cebu, Philippines were followed for 5 years. ELISA IgG≥3 was associated with reduced dengue probability relative to naïve children (3% vs. 10%, p = 0.007). Serotype-specific antibodies binding EDIII or NS1 had no association with dengue risk. Standard virus PRNT geometric mean titers (GMT) > 200 and mature GMT > 100 were associated with reduced dengue disease overall (p < 0.01). High DENV2 and DENV3 titers against either standard or mature viruses protected against the matched serotype (p < 0.01). While 43% of dengue cases had standard virus PRNT titers>100, only 2% of cases had mature virus PRNT titers>100 (p < 0.001), indicating a lower, more consistent threshold for protection. These assays may serve as correlates of protection.

Dengue fever is an important public health problem in the Philippines. In April 2016, the Department of Health launched a three-dose school based dengue vaccination program of nine- to fourteen-year-old children in three regions with the highest number of dengue cases using CYD-TDV (Dengvaxia, Sanofi Pasteur). In July 2017, a community-based dengue vaccination program was implemented in Cebu province. The program was discontinued in December 2017 amidst public controversy, after the first dose had been administered. We assessed the effectiveness of a single dose of CYD-TDV against hospitalized virologically confirmed dengue (VCD). We conducted a case-control study in Cebu province following the dengue mass vaccination. Children who were nine to fourteen years of age during the mass vaccination and subsequently admitted to any of four participating public hospitals with suspected dengue were enrolled in the study as cases. Blood for RT-PCR and clinical and socio-demographic information were obtained. To estimate the level of vaccine protection, vaccination status was compared between children with hospitalized virologically confirmed dengue and controls of the same six-year age-group as the cases, matched on sex, neighborhood and time of occurrence of cases. We enrolled 490 cases and 980 controls. Receipt of one dose of CYD-TDV was associated with 26% (95 % CI, -2 to 47%; p = 0 0675) overall protection against hospitalized virologically confirmed dengue and 51% (95 % CI, 23 to 68; p = 0 0016) protection against dengue with warning signs. A single dose of CYD-TDV given to nine to fourteen-year-old children through a community-based mass vaccination program conferred protection against dengue with warning signs and severe dengue but we were unable to conclude on protection against milder illness.

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.

Background : We previously reported an interim safety and immunogenicity analysis of a Phase 3 trial in the Philippines of the EuCorVac-19 (ECV-19) COVID-19 vaccine with the COVISHIELD^TM (CS) comparator (ClinicalTrials.gov identifier NCT05572879). Here, we present full-year humoral immunogenicity analysis. Methods: Healthy adults over 18 years of age received two injections of ECV-19 or CS vaccines, with 4 weeks between prime and boost. Analysis was carried out in individuals with immunogenicity measurements available at all 4 timepoints (weeks 0, 6, 30, and 56; n = 535 for ECV-19 and n = 260 for CS). Results: 2 weeks after boosting (week 6), ECV-19 elicited higher median anti-RBD IgG (1512 vs. 340 BAU/mL, p < 0.001) and neutralizing antibodies (1280 vs. 453 median microneutralization (MN) titer, p < 0.001) compared to CS. Anti-RBD IgG remained higher for ECV-19 compared to CS through week 30 (412 vs. 238 BAU/mL, p < 0.001) and 56 (425 vs. 260 BAU/mL, p < 0.001). MN titers remained higher for ECV-19 compared to CS through week 30 (640 vs. 453, p < 0.001) and 56 (453 vs. 320, p < 0.001). Correlation between anti-RBD IgG and neutralization titers persisted throughout the study. Women generally exhibited greater antibody responses than men. In the first six months following immunization, the ECV-19 group had a median antibody half-life of 80 days for anti-RBD IgG and 112 days for MN titer. In the subsequent six months, antibody half-life increased to 237 days for anti-RBD IgG and 168 days for MN titer. Conclusions: Following initial prime-boost vaccination, ECV-19 maintained higher anti-RBD IgG and neutralizing antibody titers relative to the CS comparator over a full-year period.

: SARS-CoV-2 serological testing is useful to determine seroprevalence, epidemiological trends, and the extent of transmission. The collection and transport of serum samples can be logistically challenging, especially in remote underserved areas. Dried blood spots (DBSs) would allow easier sample collection and logistical handling compared with standard serum collection, particularly for extensive and repeated SARS-CoV-2 serosurveys. We evaluated the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the IgG ELISA (Wantai, Beijing, China) using DBSs against sera for the quantitative detection of SARS-CoV-2 IgG antibody. The IgG ELISA was used to test paired sera and DBSs obtained from individuals with recent virologically confirmed COVID-19 illness and banked paired sera and DBSs collected before the COVID-19 pandemic. We found that 100/100 (100%) seropositive samples were positive using DBSs, and 193/194 (99%) seronegative samples were negative using DBSs. Compared with sera, the DBS method had a 100% sensitivity, 99% specificity, 99% PPV, and 100% NPV. Use of DBSs for SARS-CoV-2 household or population serosurveys may be considered in situations with limitations in sample collection, shipment, and storage.