BackgroundChikungunya virus (CHIKV) is a globally re-emerging arbovirus for which previous studies have indicated the majority of infections result in symptomatic febrile illness. We sought to characterize the proportion of subclinical and symptomatic CHIKV infections in a prospective cohort study in a country with known CHIKV circulation.Methods/FindingsA prospective longitudinal cohort of subjects ≥6 months old underwent community-based active surveillance for acute febrile illness in Cebu City, Philippines from 2012-13. Subjects with fever history were clinically evaluated at acute, 2, 5, and 8 day visits, and at a 3-week convalescent visit. Blood was collected at the acute and 3-week convalescent visits. Symptomatic CHIKV infections were identified by positive CHIKV PCR in acute blood samples and/or CHIKV IgM/IgG ELISA seroconversion in paired acute/convalescent samples. Enrollment and 12-month blood samples underwent plaque reduction neutralization test (PRNT) using CHIKV attenuated strain 181/clone25. Subclinical CHIKV infections were identified by ≥8-fold rise from a baseline enrollment PRNT titer <10 without symptomatic infection detected during the intervening surveillance period. Selected CHIKV PCR-positive samples underwent viral isolation and envelope protein-1 gene sequencing. Of 853 subjects who completed all study procedures at 12 months, 19 symptomatic infections (2.19 per 100 person-years) and 87 subclinical infections (10.03 per 100 person-years) occurred. The ratio of subclinical-to-symptomatic infections was 4.6:1 varying with age from 2:1 in 6 month-5 year olds to 12:1 in those >50 years old. Baseline CHIKV PRNT titer ≥10 was associated with 100% (95%CI: 46.1, 100.0) protection from symptomatic CHIKV infection. Phylogenetic analysis demonstrated Asian genotype closely related to strains from Asia and the Caribbean.ConclusionsSubclinical infections accounted for a majority of total CHIKV infections. A positive baseline CHIKV PRNT titer was associated with protection from symptomatic CHIKV infection. These findings have implications for assessing disease burden, understanding virus transmission, and supporting vaccine development.

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SUMMARY Severe thrombocytopenia and increased vascular permeability are two major characteristics of dengue haemorrhagic fever (DHF). To develop a better understanding of the roles of platelet-associated IgG (PAIgG) and IgM (PAIgM) in inducing thrombocytopenia and its severity of disease in patients with secondary dengue virus infection, the relationship between the PAIgG or PAIgM levels and disease severity as well as thrombocytopenia was examined in 78 patients with acute phase secondary infection in a prospective hospital-based study. The decrease in platelet count during the acute phase recovered significantly during the convalescent phase. In contrast, the increased levels of PAIgG or PAIgM that occurred during the acute phase of these patients decreased significantly during the convalescent phase. An inverse correlation between platelet count and PAIgG or PAIgM levels was found in these patients. Anti-dengue virus IgG and IgM activity was found in platelet eluates from 10 patients in an acute phase of secondary infection. Increased levels of PAIgG or PAIgM were significantly higher in DHF than those in dengue fever (DF). An increased level of PAIgM was associated independently with the development of DHF, representing a possible predictor of DHF with a high specificity. Our present data suggest that platelet-associated immunoglobulins involving antidengue virus activity play a pivotal role in the induction of thrombocytopenia and the severity of the disease in secondary dengue virus infections.

Background Takeda’s live attenuated tetravalent dengue vaccine candidate (TAK-003) is under evaluation in a long-term clinical trial across eight dengue-endemic countries. Previously, we have reported its efficacy and safety in both seronegative and seropositive participants and that its performance varies by serotype, with some decline in efficacy from first to second year post-vaccination. This exploratory analysis provides an update with cumulative and third year data. Methods Healthy 4–16 year-olds (n=20,099) were randomized 2:1 to receive TAK-003 or placebo (0, 3 month schedule). The protocol included baseline serostatus testing of all participants and detection of all symptomatic dengue throughout the trial with a serotype specific RT-PCR. Results Cumulative efficacy after three years was 62.0% (95% confidence interval: 56.6%, 66.7%) against virologically-confirmed dengue (VCD) and 83.6% (76.8%, 88.4%) against hospitalized VCD. Efficacy was 54.3% (41.9%, 64.1%) against VCD and 77.1% (58.6%, 87.3%) against hospitalized VCD in baseline seronegatives, and 65.0% (58.9%, 70.1%) against VCD and 86.0% (78.4%, 91.0%) against hospitalized VCD in seropositives. Efficacy against VCD during the third year declined to 44.7% (32.5%, 54.7%), while efficacy against hospitalized VCD was sustained at 70.8% (49.6%, 83.0%). Rates of serious adverse events were 2.9% in TAK-003 group and 3.5% in placebo group during the ongoing long-term follow-up (i.e. second half of the three years following vaccination), but none were related. No important safety risks were identified. Conclusions TAK-003 was efficacious against symptomatic dengue over three years. Efficacy declined over time but remained robust against hospitalized dengue. A booster dose evaluation is planned.

Dengue, the world's most important mosquito-borne viral disease, is endemic in the Philippines. During 2008–2012, the country's Department of Health reported an annual average of 117,065 dengue cases, placing the country fourth in dengue burden in southeast Asia. This study estimates the country's annual number of dengue episodes and their economic cost. Our comparison of cases between active and passive surveillance in Punta Princesa, Cebu City yielded an expansion factor of 7.2, close to the predicted value (7.0) based on the country's health system. We estimated an annual average of 842,867 clinically diagnosed dengue cases, with direct medical costs (in 2012 US dollars) of $345 million ($3.26 per capita). This is 54% higher than an earlier estimate without Philippines-specific costs. Ambulatory settings treated 35% of cases (representing 10% of direct costs), whereas inpatient hospitals served 65% of cases (representing 90% of direct costs). The economic burden of dengue in the Philippines is substantial.