Policymakers’ views on dengue fever/dengue haemorrhagic fever and the need for dengue vaccines in four southeast Asian countries

Dengue outbreaks in Brazil and Latin America: the new and continuing challenges

OBJECTIVES

To compare the number of suspected cases, severe cases, and deaths of dengue in 2023 and 2024 in Brazil and Latin America; and to describe its epidemiological profile.

DESIGN

Observational study.

METHODS

The data regarding dengue was retrieved from the Brazilian Ministry of Health website. The Chi-square test was used to compare the proportion of dengue cases in 2023 and 2024 according to gender, race, and age range. The odds ratio and the 95% confidence intervals were used to describe the data. The Spearman correlation test was used to compare the number of suspected cases, severe cases, and deaths of dengue with the number of distributed vaccines against dengue.

RESULTS

Dengue is one of the most common zoonoses in Latin America. In 2023, Brazil registered a total of 1,658,814 suspected cases of dengue with 1094 deaths. For 2024, a total of 1,978,372 suspected cases of dengue were reported only until the 11th epidemiological week, with 656 deaths. When comparing dengue cases reported in 2024 and 2023, there is an increase in suspected cases, with 20% more cases reported during the first 11 epidemiological weeks of 2024 than in the entire 52 epidemiological weeks of 2023. At the same time, in 2024, the Pan American Health Organization reported suspected cases in 20 Latin American countries, with 3073 cases of severe dengue and 1187 deaths. In Brazil, a different racial profile for dengue was described since Black people [OR = 1.56 (95% CI = 1.54-1.57)], Mixed individuals [OR = 1.36 (95% CI = 1.35-1.37), and Indigenous peoples [OR = 1.77 (95% CI = 1.70-1.85)] were more likely to be suspected cases of dengue in 2024 compared to 2023. Also, a positive correlation between the distributed vaccines with deaths due to dengue and the number of severe cases was described.

CONCLUSION

Brazil was responsible for more than 50% of suspected cases and deaths from dengue compared to the other Latin American countries in 2024. Furthermore, there is a different racial profile for dengue in Brazil, as Black people, Mixed individuals, and Indigenous peoples were more likely to be suspected cases of dengue in 2024 compared to 2023.

Key decision-making factors for human papillomavirus (HPV) vaccine program introduction in low-and-middle-income-countries: Global and national stakeholder perspectives

Low-and-middle-income countries (LMICs) experience a high burden of cervical cancer. The human papillomavirus (HPV) vaccine prevents high-risk strains of HPV that cause cervical cancer; however, the integration of HPV vaccines into national immunization programs within many LMICs has been suboptimal. Our study evaluated key factors that drive the decision-making process for the implementation of HPV vaccine programs in LMICs. Stakeholder analysis and semi-structured in-depth interviews were conducted with national and global stakeholders. Interview data were analyzed through qualitative descriptive methods. Findings from our study revealed the decision-making process for HPV vaccines requires the involvement of multiple institutions and stakeholders from national and global levels, with decision-making being a country-specific process. Partner considerations, locally driven processes, availability of data, and infrastructure and resource considerations were found to be critical factors in the decision-making process. Future programs should evaluate the best approaches for investing in initiatives to enhance coordination, ensure vaccine introduction is locally driven, increase the availability of data needed for decision-making, and equip countries with the necessary resources to guide country decision-making in the face of increasingly complex decision-making environments.

Using a health belief model to assess COVID-19 vaccine intention and hesitancy in Jakarta, Indonesia

Since January 2021, Indonesia has administered a nationwide COVID-19 vaccination. This study examined vaccine intention and identified reasons for vaccine hesitancy in the capital city of Jakarta. This is a cross-sectional online survey using the Health Belief Model (HBM) to assess vaccine intent predictors and describe reasons for hesitancy among Jakarta residents. Among 11,611 respondents, 92.99% (10.797) would like to get vaccinated. This study indicated that all HBM constructs predict vaccine intention (P< 0.05). Those with a high score of perceived susceptibility to the COVID-19 vaccine were significantly predicted vaccine hesitancy (OR = 0.18, 95% CI: 0.16-0.21). Perceived higher benefits of COVID-19 vaccine (OR = 2.91, 95% CI: 2.57-3.28), perceived severity of COVID-19 disease (OR: 1.41, 95% CI: 1.24-1.60), and perceived susceptibility of the current pandemic (OR = 1.21, 95% CI: 1.06-1.38) were significantly predicted vaccination intend. Needle fears, halal concerns, vaccine side effects, and the perception that vaccines could not protect against COVID-19 disease emerged as reasons why a small portion of the respondents (n = 814, 7.23%) are hesitant to get vaccinated. This study demonstrated a high COVID-19 vaccine intention and highlighted the reasons for vaccine refusal, including needle fears, susceptibility to vaccine efficacy, halal issues, and concern about vaccine side effects. The current findings on COVID-19 vaccination show that the government and policymakers should take all necessary steps to remove vaccine hesitancy by increasing awareness of vaccine efficacy and benefit interventions.

Comparing machine learning with case-control models to identify confirmed dengue cases

In recent decades, the global incidence of dengue has increased. Affected countries have responded with more effective surveillance strategies to detect outbreaks early, monitor the trends, and implement prevention and control measures. We have applied newly developed machine learning approaches to identify laboratory-confirmed dengue cases from 4,894 emergency department patients with dengue-like illness (DLI) who received laboratory tests. Among them, 60.11% (2942 cases) were confirmed to have dengue. Using just four input variables [age, body temperature, white blood cells counts (WBCs) and platelets], not only the state-of-the-art deep neural network (DNN) prediction models but also the conventional decision tree (DT) and logistic regression (LR) models delivered performances with receiver operating characteristic (ROC) curves areas under curves (AUCs) of the ranging from 83.75% to 85.87% [for DT, DNN and LR: 84.60% ± 0.03%, 85.87% ± 0.54%, 83.75% ± 0.17%, respectively]. Subgroup analyses found all the models were very sensitive particularly in the pre-epidemic period. Pre-peak sensitivities (<35 weeks) were 92.6%, 92.9%, and 93.1% in DT, DNN, and LR respectively. Adjusted odds ratios examined with LR for low WBCs [≤ 3.2 (x103/μL)], fever (≥38°C), low platelet counts [< 100 (x103/μL)], and elderly (≥ 65 years) were 5.17 [95% confidence interval (CI): 3.96-6.76], 3.17 [95%CI: 2.74-3.66], 3.10 [95%CI: 2.44-3.94], and 1.77 [95%CI: 1.50-2.10], respectively. Our prediction models can readily be used in resource-poor countries where viral/serologic tests are inconvenient and can also be applied for real-time syndromic surveillance to monitor trends of dengue cases and even be integrated with mosquito/environment surveillance for early warning and immediate prevention/control measures. In other words, a local community hospital/clinic with an instrument of complete blood counts (including platelets) can provide a sentinel screening during outbreaks. In conclusion, the machine learning approach can facilitate medical and public health efforts to minimize the health threat of dengue epidemics. However, laboratory confirmation remains the primary goal of surveillance and outbreak investigation.

Hidden heterogeneity and its influence on dengue vaccination impact

The CYD-TDV vaccine was recently developed to combat dengue, a mosquito-borne viral disease that afflicts millions of people each year throughout the tropical and subtropical world. Its rollout has been complicated by recent findings that vaccinees with no prior exposure to dengue virus (DENV) experience an elevated risk of severe disease in response to their first DENV infection subsequent to vaccination. As a result of these findings, guidelines for use of CYD-TDV now require serological screening prior to vaccination to establish that an individual does not fall into this high-risk category. These complications mean that the public health impact of CYD-TDV vaccination is expected to be higher in areas with higher transmission. One important practical difficulty with tailoring vaccination policy to local transmission contexts is that DENV transmission is spatially heterogeneous, even at the scale of neighborhoods or blocks within a city. This raises the question of whether models based on data that average over spatial heterogeneity in transmission could fail to capture important aspects of CYD-TDV impact in spatially heterogeneous populations. We explored this question with a deterministic model of DENV transmission and CYD-TDV vaccination in a population comprised of two communities with differing transmission intensities. Compared to the full model, a version of the model based on the average of the two communities failed to capture benefits of targeting the intervention to the high-transmission community, which resulted in greater impact in both communities than we observed under even coverage. In addition, the model based on the average of the two communities substantially overestimated impact among vaccinated individuals in the low-transmission community. In the event that the specificity of serological screening is not high, this result suggests that models that ignore spatial heterogeneity could overlook the potential for harm to this segment of the population.

Hypothetical assessment of efficiency, willingness-to-accept and willingness-to-pay for dengue vaccine and treatment: a contingent valuation survey in Bangladesh

In 2019, Bangladesh has grappled with a record-breaking surge in dengue fever, experiencing the highest number of dengue cases since the year 2000. Together, the intensification of dengue fever combined with a lack of dengue vaccines and appropriate medicines is expected to further the public and government's interests in appropriate and potential dengue vaccines to control the epidemic. We considered people's characteristics, dengue experience, and knowledge to assess their willingness-to-accept (WTA) and willingness-to-pay (WTP) for a hypothetical dengue vaccine and ex-post treatment in Bangladesh (June-July 2019). This study implemented a contingent valuation (CV) method with 3,251 respondents in 10 different locations of Bangladesh. All respondents participated in a hypothetical dengue vaccine scenario consisting of 65% (vaccine A), 80% (vaccine B), and 95% (vaccine C) effectiveness levels with three doses of each vaccine and ex-post dengue treatment. Around 71.2% of respondents were willing to pay for at least one of the hypothetical vaccines: A, B, or C. The average WTPs of the three vaccines amounted to US$ 47.0, US$ 66.0, and US$ 89.0, which were defined as the total cost of the doses necessary to obtain immunity. In Bangladesh, there is a significant demand for low-priced dengue vaccines, which was proven by people's higher acceptance of vaccination practices. Though dengue vaccines are not yet available in Bangladesh, this study provides significant support that both the government and private sectors should work together to develop a reliable and affordable dengue vaccine.

Dengue: A Minireview

Dengue, caused by infection of any of four dengue virus serotypes (DENV-1 to DENV-4), is a mosquito-borne disease of major public health concern associated with significant morbidity, mortality, and economic cost, particularly in developing countries. Dengue incidence has increased 30-fold in the last 50 years and over 50% of the world’s population, in more than 100 countries, live in areas at risk of DENV infection. We reviews DENV biology, epidemiology, transmission dynamics including circulating serotypes and genotypes, the immune response, the pathogenesis of the disease as well as updated diagnostic methods, treatments, vector control and vaccine developments.

Trends in dengue research in the Philippines: A systematic review

Dengue is an important public health problem in the Philippines. We sought to describe the trends in dengue research in the country. We searched four databases and identified published studies on dengue research in the Philippines during the past 60 years. We reviewed 135 eligible studies, of which 33% were descriptive epidemiologic studies or case series, 16% were entomologic or vector control studies, 12% were studies on dengue virology and serologic response, 10% were socio-behavioral and economics studies, 8% were clinical trials, 7% were on burden of disease, 7% were investigations on markers of disease severity, 5% were on dengue diagnostics, and 2% were modeling studies. During the last decade, dengue research in the Philippines has increased and evolved from simple descriptive studies to those with more complex and diverse designs. We identified several key topics where more research would be useful.

Customers' preferences and willingness to pay for a future dengue vaccination: a study of the empirical evidence in Vietnam

BACKGROUND

Dengue was endemic to Vietnam. Due to the lack of a readily available remedy, dengue vaccines (DV) have been used elsewhere to cure the disease. However, introducing DV in Vietnam has met resistance from society and the government, influencing decisions about willingness-to-pay (WTP) and other pharmacoeconomic studies. This research aimed to evaluate the extent to which Vietnamese customers would be willing to pay to vaccinate themselves and their children, if any at all, against dengue.

MATERIALS AND METHODS

This was a cross-sectional interview-based research. Contingent valuation method, combined with the bidding technique and several open-ended questions, were used to obtain the maximum WTP values for six hypothetical scenarios of two types of DV (60% efficacy for 10 years, "Type 1" vs 90% efficacy for 20 years, "Type 2").

RESULTS

The median WTP per adult for Type 1 and Type 2 DV were US$130.34 and US$217.39, respectively. The median WTP rates per parent for their own vaccination were US$86.96 (Type 1) and US$156.52 (Type 2), for their children vaccination costs were US$108.70 (Type 1) and US$195.65 (Type 2). Five factors affected the WTP rates: monthly income, marital status, area, locality and level of education.

CONCLUSION

The WTP rates for DV were high, supporting the introduction of DV in Vietnam.

Feasibility and willingness to pay for dengue vaccine in the threat of dengue fever outbreaks in Vietnam

BACKGROUND

The escalation of dengue fever (DF) cases in recent years and the occurrence of a large-scale DF outbreak in 2017 underline the importance of dengue vaccines in Vietnam. Given the potential benefits of the dengue vaccines and the need for copayment by the private sector, this study aims to evaluate the willingness to pay (WTP) for the dengue vaccines in patients with DF in Northern Vietnam.

METHODS

A cross-sectional study was conducted on 330 in-and-out patients with DF admitted to the Bach Mai Hospital. We used the contingent valuation method to evaluate the WTP for dengue vaccines. Socioeconomic and clinical characteristics were also investigated. Multivariate interval and logistic regression models were used to estimate the average amount of WTP and identify the factors associated with the WTP.

RESULTS

Around 77.3% patients were willing to pay an average amount of US$ 67.4 (95% CI=57.4-77.4) for the vaccine. People of higher ages, those having health insurance, those traveling in the past 15 days or suffering from anxiety/depression were less likely to be willing to pay for the dengue vaccine. However, people having a longer duration of DF or having problems with mobility were positively associated with WTP for the dengue vaccine. Patients educated to more than high school levels (Coeff.=31.31; 95% CI=3.26-59.35), those in the richest quintile (Coeff.=62.76; 95% CI=25.40; 100.13), or those having a longer duration of the disease (Coeff.=6.18; 95% CI=0.72-11.63) were willing to pay a higher amount.

CONCLUSION

This study highlights a relatively high rate and amount of WTP for the dengue vaccine among patients with DF. Psychological counseling services as well as educational campaigns should be undertaken to improve the WTP for the vaccine. Moreover, government subsidies should be given to increase the coverage of the vaccine in the future, especially for the poor.

Prevention and Control Strategies to Counter Dengue Virus Infection

Dengue is currently the highest and rapidly spreading vector-borne viral disease, which can lead to mortality in its severe form. The globally endemic dengue poses as a public health and economic challenge that has been attempted to suppress though application of various prevention and control techniques. Therefore, broad spectrum techniques, that are efficient, cost-effective, and environmentally sustainable, are proposed and practiced in dengue-endemic regions. The development of vaccines and immunotherapies have introduced a new dimension for effective dengue control and prevention. Thus, the present study focuses on the preventive and control strategies that are currently employed to counter dengue. While traditional control strategies bring temporary sustainability alone, implementation of novel biotechnological interventions, such as sterile insect technique, paratransgenesis, and production of genetically modified vectors, has improved the efficacy of the traditional strategies. Although a large-scale vector control strategy can be limited, innovative vaccine candidates have provided evidence for promising dengue prevention measures. The use of tetravalent dengue vaccine (CYD-TDV) has been the most effective so far in treating dengue infections. Nonetheless, challenges and limitation hinder the progress of developing integrated intervention methods and vaccines; while the improvement in the latest techniques and vaccine formulation continues, one can hope for a future without the threat of dengue virus.

Disease Burden of Dengue in the Philippines: Adjusting for Underreporting by Comparing Active and Passive Dengue Surveillance in Punta Princesa, Cebu City

AbstractDengue virus (DENV) is a serious threat to public health. Having reliable estimates of the burden of dengue is important to inform policy and research, but surveillance systems are not designed to capture all symptomatic DENV infections. We derived the rate of reporting of dengue by comparing active surveillance of symptomatic DENV infections in a prospective community-based seroepidemiological cohort study (N = 1008) of acute febrile illness in Punta Princesa, Cebu City, Philippines, with passive surveillance data from the Cebu City Health Department. Febrile episodes detected in a weekly follow-up of participants were tested for serotype-specific DENV by hemi-nested reverse transcription-polymerase chain reaction (nested RT-PCR) and acute/convalescent blood samples tested by dengue IgM/IgG enzyme immunoassay. We estimated the burden of dengue in the Philippines in disability-adjusted life years (DALYs), and conducted a probabilistic sensitivity analysis using Monte-Carlo simulations to address uncertainty. The results showed a 21% cumulative reporting rate of symptomatic DENV infections, equivalent to an expansion factor of 4.7 (95% certainty level [CL]: 2.2-15.1). Based on surveillance data in the Philippines for 2010-2014, we estimated 794,255 annual dengue episodes (95% CL: 463,000-2,076,000) and a disease burden of 535 (95% CL: 380-994) DALYs per million population using age weights and time discounting and 997 (95% CL: 681-1,871) DALYs per million population without age and time adjustments. Dengue imposes a substantial burden in the Philippines; almost 10 times higher than estimated for rabies, about twice the burden of intestinal fluke infections, and about 10% of the burden of tuberculosis. Our estimates should inform policy makers and raise awareness among the public.

Three Decades of Dengue Surveillance in Five Highly Endemic South East Asian Countries

We described and quantified epidemiologic trends in dengue disease burden in 5 Asian countries (Indonesia, Thailand, Malaysia, Philippines, and Vietnam) and identified and estimated outbreaks impact over the last 3 decades. Dengue surveillance data from 1980 to 2010 were retrieved from DengueNet and from World Health Organization sources. Trends in incidence, mortality, and case fatality rate (CFR) were systematically analyzed using annual average percent change (AAPC), and the contribution of epidemic years identified over the observation period was quantified. Over the 30-year period, incidence increased in all countries (AAPC 1980-2010: 6.7% in Thailand, 10.4% in Vietnam, 12.0% in Indonesia, 18.1% in Malaysia, 24.4% in Philippines). Mortality also increased in Indonesia, Malaysia, and Philippines (AAPC: 6.8%, 7.0%, and 29.2%, respectively), but slightly decreased in Thailand and Vietnam (AAPC: −1.3% and −2.5%), and CFR decreased in all countries (AAPC: −4.2% to −8.3%). Epidemic years, despite representing less than a third of the observation period, contributed from 1 to 3 times more cases versus nonepidemic years. Implementation of more sensitive surveillance methods over the study period may have contributed to a reporting or ascertainment bias in some countries. Nonetheless, these data support the urgent need for novel, integrated, or otherwise effective dengue prevention and control tools and approaches.

Modifiable determinants of attitude towards dengue vaccination among healthy inhabitants of Aceh, Indonesia: Findings from a community-based survey

OBJECTIVE

To explore and understand the attitude towards dengue vaccination and its modifiable determinants among inhabitants of Aceh (northern Sumatra Island, Indonesia), the region that was most severely affected by the earthquake and tsunami of 26 December 2004.

METHODS

A community-based, cross-sectional study was conducted among 535 healthy inhabitants in nine regencies (Kabupaten or Kotamadya) of Aceh that were selected randomly from November 2014 to March 2015. A set of validated, pre-tested, structured questionnaires was used to guide the interviews. The questionnaires covered a range of explanatory variables and one outcome variable (attitude to dengue vaccination). Multi-step logistic regression analysis and Spearman's rank correlation were used to test the role of explanatory variables for the outcome variable.

RESULTS

More than 70% of the participants had a poor attitude towards dengue vaccination. Modifiable determinants associated with poor attitude to dengue vaccination were low education level, working as farmers and traditional market traders, low socioeconomic status and poor knowledge, attitude and practice regarding dengue fever (P < 0.05). The KAP domain scores were correlated strongly with attitude to dengue vaccination, rs = 0.25, rs = 0.67 and rs = 0.20, respectively (P < 0.001). Multivariate analysis found that independent predictors associated with attitude towards dengue vaccination among study participants were only sex and attitude towards dengue fever (P < 0.001).

CONCLUSIONS

This study reveals that low KAP regarding dengue fever, low education level and low socioeconomic status are associated with a poor attitude towards dengue vaccination. Therefore, inhabitants of suburbs who are working as farmers or traditional market traders with low socioeconomic status are the most appropriate target group for a dengue vaccine introduction program.

Current issues in the economics of vaccination against dengue

Dengue is a major public health concern in tropical and subtropical areas of the world. The prospects for dengue prevention have recently improved with the results of efficacy trials of a tetravalent dengue vaccine. Although partially effective, once licensed, its introduction can be a public health priority in heavily affected countries because of the perceived public health importance of dengue. This review explores the most immediate economic considerations of introducing a new dengue vaccine and evaluates the published economic analyses of dengue vaccination. Findings indicate that the current economic evidence base is of limited utility to support country-level decisions on dengue vaccine introduction. There are a handful of published cost-effectiveness studies and no country-specific costing studies to project the full resource requirements of dengue vaccine introduction. Country-level analytical expertise in economic analyses, another gap identified, needs to be strengthened to facilitate evidence-based decision-making on dengue vaccine introduction in endemic countries.

A Multi-country Study of the Household Willingness-to-Pay for Dengue Vaccines: Household Surveys in Vietnam, Thailand, and Colombia

Background

The rise in dengue fever cases and the absence of dengue vaccines will likely cause governments to consider various types of effective means for controlling the disease. Given strong public interests in potential dengue vaccines, it is essential to understand the private economic benefits of dengue vaccines for accelerated introduction of vaccines into the public sector program and private markets of high-risk countries.

Methodology/Principal Findings

A contingent valuation study for a hypothetical dengue vaccine was administered to 400 households in a multi-country setting: Vietnam, Thailand, and Colombia. All respondents received a description of the hypothetical dengue vaccine scenarios of 70% or 95% effectiveness for 10 or 30 years with a three dose series. Five price points were determined after pilot tests in order to reflect different local situations such as household income levels and general perceptions towards dengue fever. We adopted either Poisson or negative binomial regression models to calculate average willingness-to-pay (WTP), as well as median WTP. We found that there is a significant demand for dengue vaccines. The parametric median WTP is $26.4 ($8.8 per dose) in Vietnam, $70.3 ($23.4 per dose) in Thailand, and $23 ($7.7 per dose) in Colombia. Our study also suggests that respondents place more value on vaccinating young children than school age children and adults.

Conclusions/Significance

Knowing that dengue vaccines are not yet available, our study provides critical information to both public and private sectors. The study results can be used to ensure broad coverage with an affordable price and incorporated into cost benefit analyses, which can inform prioritization of alternative health interventions at the national level.

Dengue is complicated. There are four serotypes of the dengue virus, and dengue infection occurs in almost all age groups. Infection with one serotype provides life-long immunity to that specific serotype but does not protect against the other three serotypes. Unlike other diseases which already have preventable vaccines developed, currently there are no commercially available vaccines for dengue fever. Even if the first vaccine becomes available, it is expected that there will be a limited number of vaccine doses available in the first few years. Due to the increase in dengue fever cases, there is already huge public and private interest in potential dengue vaccines. This study reports the household willingness-to-pay for a hypothetical dengue vaccine in three dengue endemic countries. We found that household demand is strongly related to price and income. It was also observed that more than half of the study populations are willing to pay for vaccines when price is lower than the median estimates reported here. This study may contribute to a more effective decision on dengue vaccine introduction.

Acceptability of hypothetical dengue vaccines among travelers

BACKGROUND

Dengue viruses have spread widely in recent decades and cause tens of millions of infections mostly in tropical and subtropical areas. Vaccine candidates are being studied aggressively and may be ready for licensure soon.

METHODS

We surveyed patients with past or upcoming travel to dengue-endemic countries to assess rates and determinants of acceptance for four hypothetical dengue vaccines with variable efficacy and adverse event (AE) profiles. Acceptance ratios were calculated for vaccines with varied efficacy and AE risk.

RESULTS

Acceptance of the four hypothetical vaccines ranged from 54% for the vaccine with lower efficacy and serious AE risk to 95% for the vaccine with higher efficacy and minor AE risk. Given equal efficacy, vaccines with lower AE risk were better accepted than those with higher AE risk; given equivalent AE risk, vaccines with higher efficacy were better accepted than those with lower efficacy. History of Japanese encephalitis vaccination was associated with lower vaccine acceptance for one of the hypothetical vaccines. US-born travelers were more likely than non-US born travelers to accept a vaccine with 75% efficacy and a risk of minor AEs (p = 0.003). Compared with North American-born travelers, Asian- and African-born travelers were less likely to accept both vaccines with 75% efficacy.

CONCLUSIONS

Most travelers would accept a safe and efficacious dengue vaccine if one were available. Travelers valued fewer potential AEs over increased vaccine efficacy.

Public acceptance and willingness-to-pay for a future dengue vaccine: a community-based survey in Bandung, Indonesia

BACKGROUND

All four serotypes of dengue virus are endemic in Indonesia, where the population at risk for infection exceeds 200 million people. Despite continuous control efforts that were initiated more than four decades ago, Indonesia still suffers from multi-annual cycles of dengue outbreak and dengue remains as a major public health problem. Dengue vaccines have been viewed as a promising solution for controlling dengue in Indonesia, but thus far its potential acceptability has not been assessed.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a household survey in the city of Bandung, Indonesia by administering a questionnaire to examine (i) acceptance of a hypothetical pediatric dengue vaccine; (ii) participant's willingness-to-pay (WTP) for the vaccine, had it not been provided for free; and (iii) whether people think vector control would be unnecessary if the vaccine was available. A proportional odds model and an interval regression model were employed to identify determinants of acceptance and WTP, respectively. We demonstrated that out of 500 heads of household being interviewed, 94.2% would agree to vaccinate their children with the vaccine. Of all participants, 94.6% were willing to pay for the vaccine with a median WTP of US$1.94. In addition, 7.2% stated that vector control would not be necessary had there been a dengue vaccination program.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that future dengue vaccines can have a very high uptake even when delivered through the private market. This, however, can be influenced by vaccine characteristics and price. In addition, reduction in community vector control efforts may be observed following vaccine introduction but its potential impact in the transmission of dengue and other vector-borne diseases requires further study.

Dengue vaccines: recent developments, ongoing challenges and current candidates

Dengue is among the most prevalent and important arbovirus diseases of humans. To effectively control this rapidly spreading disease, control of the vector mosquito and a safe and efficacious vaccine are critical. Despite considerable efforts, the development of a successful vaccine has remained elusive. Multiple factors have complicated the creation of a successful vaccine, not the least of which are the complex, immune-mediated responses against four antigenically distinct serotypes necessitating a tetravalent vaccine providing long-lasting protective immunity. Despite the multiple impediments, there are currently many promising vaccine candidates in preclinical and clinical development. Here, the recent advances in dengue virus vaccine development are reviewed and the challenges associated with the use of these vaccines as a public health tool are briefly discussed.

Will dengue vaccines be used in the public sector and if so, how? Findings from an 8-country survey of policymakers and opinion leaders

Background

A face-to-face survey of 158 policymakers and other influential professionals was conducted in eight dengue-endemic countries in Asia (India, Sri Lanka, Thailand, Vietnam) and Latin America (Brazil, Colombia, Mexico, Nicaragua) to provide an indication of the potential demand for dengue vaccination in endemic countries, and to anticipate their research and other requirements in order to make decisions about the introduction of dengue vaccines. The study took place in anticipation of the licensure of the first dengue vaccine in the next several years.

Methods/Principal Findings

Semi-structured interviews were conducted on an individual or small group basis with government health officials, research scientists, medical association officers, vaccine producers, local-level health authorities, and others considered to have a role in influencing decisions about dengue control and vaccines. Most informants across countries considered dengue a priority disease and expressed interest in the public sector use of dengue vaccines, with a major driver being the political pressure from the public and the medical community to control the disease. There was interest in a vaccine that protects children as young as possible and that can fit into existing childhood immunization schedules. Dengue vaccination in most countries surveyed will likely be targeted to high-risk areas and begin with routine immunization of infants and young children, followed by catch-up campaigns for older age groups, as funding permits. Key data requirements for decision-making were additional local dengue surveillance data, vaccine cost-effectiveness estimates, post-marketing safety surveillance data and, in some countries vaccine safety and immunogenicity data in the local population.

Conclusions/Significance

The lookout for the public sector use of dengue vaccines in the eight countries appears quite favorable. Major determinants of whether and when countries will introduce dengue vaccines include whether WHO recommends the vaccines, their price, the availability of external financing for lower income countries, and whether they can be incorporated into countries' routine immunization schedules.

Information gleaned from surveys of country-level policymakers and other opinion leaders can assist in planning the development, production and introduction of new or upcoming vaccines into public sector immunization programs. In the case of dengue vaccines, prevailing views among these leaders about the importance of the disease, their expressed level of interest in the government's use of the vaccine, and preferred strategies for vaccine introduction (e.g., geographically-targeted vs. nation-wide vaccination, specific age groups to target) can help to identify “early adopter” countries and indicate the level of demand for the vaccine. This information can be critical to current producers of the vaccine in planning their production capacity and to potential future producers in deciding whether to pursue development of the vaccine. This information also helps donors and international technical agencies, such as WHO and UNICEF, in setting their priorities and determining their level of technical and financial support to countries for the introduction of dengue vaccines. In addition, these surveys can provide crucial information to national governments and the above stakeholders about potential barriers to introducing dengue vaccines into national immunization programs, and what additional studies and data countries will require in order to make decisions about use of the vaccines in the public sector.

Spatial and temporal patterns of dengue in Guangdong province of China

The aim of the study was to describe the spatial and temporal patterns of dengue in Guangdong for 1978 to 2010. Time series analysis was performed using data on annual dengue incidence in Guangdong province for 1978-2010. Annual average dengue incidences for each city were mapped for 4 periods by using the geographical information system (GIS). Hot spot analysis was used to identify spatial patterns of dengue cases for 2005-2010 by using the CrimeStat III software. The incidence of dengue in Guangdong province had fallen steadily from 1978 to 2010. The time series was a random sequence without regularity and with no fixed cycle. The geographic range of dengue fever had expanded from 1978 to 2010. Cases were mostly concentrated in Zhanjiang and the developed regions of Pearl River Delta and Shantou.

Lessons from malaria control to help meet the rising challenge of dengue

Achievements in malaria control could inform efforts to control the increasing global burden of dengue. Better methods for quantifying dengue endemicity-equivalent to parasite prevalence surveys and endemicity mapping used for malaria-would help target resources, monitor progress, and advocate for investment in dengue prevention. Success in controlling malaria has been attributed to widespread implementation of interventions with proven efficacy. An improved evidence base is needed for large-scale delivery of existing and novel interventions for vector control, alongside continued investment in dengue drug and vaccine development. Control of dengue is unlikely to be achieved without coordinated international financial and technical support for national programmes, which has proven effective in reducing the global burden of malaria.

Dengue infection in children in Ratchaburi, Thailand: a cohort study. II. Clinical manifestations

BACKGROUND

Dengue infection is one of the most important mosquito-borne diseases. More data regarding the disease burden and the prevalence of each clinical spectrum among symptomatic infections and the clinical manifestations are needed. This study aims to describe the incidence and clinical manifestations of symptomatic dengue infection in Thai children during 2006 through 2008.

STUDY DESIGN

This study is a school-based prospective open cohort study with a 9,448 person-year follow-up in children aged 3-14 years. Active surveillance for febrile illnesses was done in the studied subjects. Subjects who had febrile illness were asked to visit the study hospital for clinical and laboratory evaluation, treatment, and serological tests for dengue infection. The clinical data from medical records, diary cards, and data collection forms were collected and analyzed.

RESULTS

Dengue infections were the causes of 12.1% of febrile illnesses attending the hospital, including undifferentiated fever (UF) (49.8%), dengue fever (DF) (39.3%) and dengue hemorrhagic fever (DHF) (10.9%). Headache, anorexia, nausea/vomiting and myalgia were common symptoms occurring in more than half of the patients. The more severe dengue spectrum (i.e., DHF) had higher temperature, higher prevalence of nausea/vomiting, abdominal pain, rash, diarrhea, petechiae, hepatomegaly and lower platelet count. DHF cases also had significantly higher prevalence of anorexia, nausea/vomiting and abdominal pain during day 3-6 and diarrhea during day 4-6 of illness. The absence of nausea/vomiting, abdominal pain, diarrhea, petechiae, hepatomegaly and positive tourniquet test may predict non-DHF.

CONCLUSION

Among symptomatic dengue infection, UF is most common followed by DF and DHF. Some clinical manifestations may be useful to predict the more severe disease (i.e., DHF). This study presents additional information in the clinical spectra of symptomatic dengue infection.

Safety and immunogenicity of a tetravalent live-attenuated dengue vaccine in flavivirus-naive infants

A Phase I/II observer-blind, randomized, controlled trial evaluated the safety and immunogenicity of a dengue virus (DENV) vaccine candidate in healthy Thai infants (aged 12-15 months) without measurable pre-vaccination neutralizing antibodies to DENV and Japanese encephalitis virus. Fifty-one subjects received two doses of either DENV (N = 34; four received 1/10th dose) or control vaccine (N = 17; dose 1, live varicella; dose 2, Haemophilus influenzae type b). After each vaccine dose, adverse events (AEs) were solicited for 21 days, and non-serious AEs were solicited for 30 days; serious AEs (SAEs) were recorded throughout the study. Laboratory safety assessments were performed at 10 and 30 days; neutralizing antibodies were measured at 30 days. The DENV vaccine was well-tolerated without any related SAEs. After the second dose, 85.7% of full-dose DENV vaccinees developed at least trivalent and 53.6% developed tetravalent neutralizing antibodies ≥ 1:10 to DENV (control group = 0%). This vaccine candidate, therefore, warrants continued development in this age group (NCT00322049; clinicaltrials.gov).

Under-recognition and reporting of dengue in Cambodia: a capture–recapture analysis of the National Dengue Surveillance System

Robust disease burden estimates are important for decision-making concerning introduction of new vaccines. Dengue is a major public health problem in the tropics but robust disease burden estimates are lacking. We conducted a two-sample, capture–recapture study in the largest province in Cambodia to determine disease under-recognition to the National Dengue Surveillance System (NDSS). During 2006–2008, community-based active surveillance for acute febrile illness was conducted in 0- to 19-year-olds in rural and urban areas combined with testing for dengue virus infection. Of 14 354 individuals under active surveillance (22 498 person-seasons), the annual incidence ranged from 13·4 to 57·8/1000 person-seasons. During the same period, NDSS incidence rates ranged from 1·1/1000 to 5·7/1000, which was 3·9- to 29·0-fold lower than found in the capture–recapture study. In hospitalized cases, the rate of under-recognition was 1·1- to 2·4-fold. This study shows the substantial degree of under-recognition/reporting of dengue and that reported hospitalized cases are not a good surrogate for estimating dengue disease burden.

Health economics of dengue: a systematic literature review and expert panel's assessment

Dengue vaccines are currently in development and policymakers need appropriate economic studies to determine their potential financial and public health impact. We searched five databases (PubMed, EMBASE, LILAC, EconLit, and WHOLIS) to identify health economics studies of dengue. Forty-three manuscripts were identified that provided primary data: 32 report economic burden of dengue and nine are comparative economic analyses assessing various interventions. The remaining two were a willingness-to-pay study and a policymaker survey. An expert panel reviewed the existing dengue economic literature and recommended future research to fill information gaps. Although dengue is an important vector-borne disease, the economic literature is relatively sparse and results have often been conflicting because of use of inconsistent assumptions. Health economic research specific to dengue is urgently needed to ensure informed decision making on the various options for controlling and preventing this disease.

Dengue incidence in urban and rural Cambodia: results from population-based active fever surveillance, 2006-2008

Background

Dengue vaccines are now in late-stage development, and evaluation and robust estimates of dengue disease burden are needed to facilitate further development and introduction. In Cambodia, the national dengue case-definition only allows reporting of children less than 16 years of age, and little is known about dengue burden in rural areas and among older persons. To estimate the true burden of dengue in the largest province of Cambodia, Kampong Cham, we conducted community-based active dengue fever surveillance among the 0-to-19–year age group in rural villages and urban areas during 2006–2008.

Methods and Findings

Active surveillance for febrile illness was conducted in 32 villages and 10 urban areas by mothers trained to use digital thermometers combined with weekly home visits to identify persons with fever. An investigation team visited families with febrile persons to obtain informed consent for participation in the follow-up study, which included collection of personal data and blood specimens. Dengue-related febrile illness was defined using molecular and serological testing of paired acute and convalescent blood samples. Over the three years of surveillance, 6,121 fever episodes were identified with 736 laboratory-confirmed dengue virus (DENV) infections for incidences of 13.4–57.8/1,000 person-seasons. Average incidence was highest among children less than 7 years of age (41.1/1,000 person-seasons) and lowest among the 16-to-19–year age group (11.3/1,000 person-seasons). The distribution of dengue was highly focal, with incidence rates in villages and urban areas ranging from 1.5–211.5/1,000 person-seasons (median 36.5). During a DENV-3 outbreak in 2007, rural areas were affected more than urban areas (incidence 71 vs. 17/1,000 person-seasons, p<0.001).

Conclusion

The large-scale active surveillance study for dengue fever in Cambodia found a higher disease incidence than reported to the national surveillance system, particularly in preschool children and that disease incidence was high in both rural and urban areas. It also confirmed the previously observed focal nature of dengue virus transmission.

Dengue is a major public health problem in South-East Asia. Several dengue vaccine candidates are now in late-stage development and are being evaluated in clinical trials. Accurate estimates of true dengue disease burden will become an important factor in the public-health decision-making process for endemic countries once safe and effective vaccines become available. However, estimates of the true disease incidence are difficult to make, because national surveillance systems suffer from disease under-recognition and reporting. Dengue is mainly reported among children, and in some countries, such as Cambodia, the national case definition only includes hospitalized children. This study used active, community-based surveillance of febrile illness coupled with laboratory testing for DENV infection to identify cases of dengue fever in rural and urban populations. We found a high burden of dengue in young children and late adolescents in both rural and urban communities at a magnitude greater than previously described. The study also confirmed the previously observed focal nature of dengue virus transmission.

Best practices in dengue surveillance: a report from the Asia-Pacific and Americas Dengue Prevention Boards

BACKGROUND

Dengue fever is a virus infection that is spread by the Aedes aegypti mosquito and can cause severe disease especially in children. Dengue fever is a major problem in tropical and sub-tropical regions of the world.

METHODOLOGY/PRINCIPAL FINDINGS

We invited dengue experts from around the world to attend meetings to discuss dengue surveillance. We reviewed literature, heard detailed reports on surveillance programs, and shared expert opinions.

RESULTS

Presentations by 22 countries were heard during the 2.5 day meetings. We describe the best methods of surveillance in general, the stakeholders in dengue surveillance, and the steps from mosquito bite to reporting of a dengue case to explore how best to carry out dengue surveillance. We also provide details and a comparison of the dengue surveillance programs by the presenting countries.

CONCLUSIONS/SIGNIFICANCE

The experts provided recommendations for achieving the best possible data from dengue surveillance accepting the realities of the real world (e.g., limited funding and staff). Their recommendations included: (1) Every dengue endemic country should make reporting of dengue cases to the government mandatory; (2) electronic reporting systems should be developed and used; (3) at minimum dengue surveillance data should include incidence, hospitalization rates, deaths by age group; (4) additional studies should be completed to check the sensitivity of the system; (5) laboratories should share expertise and data; (6) tests that identify dengue virus should be used in patients with fever for four days or less and antibody tests should be used after day 4 to diagnose dengue; and (7) early detection and prediction of dengue outbreaks should be goals for national surveillance systems.

Forecasting dengue vaccine demand in disease endemic and non-endemic countries

BACKGROUND

A dengue vaccine in large-scale clinical trials could be licensed in several years. We estimated the potential vaccine demand for different introduction strategies in 54 dengue-endemic countries and for travelers from non-endemic countries to enable vaccine producers and public health agencies to better prepare for timely utilization of the vaccine.

RESULTS

Under our assumptions, 2.4-3.5 billion dengue vaccine doses would be needed in the first five years after introduction with >75% delivered in the public sector. Among 20 potential 'early-adopter' countries, an estimated 0.9-1.4 billion doses would be needed for the same introduction approach. For the private sector, covering 10% of children and 30% of adults an estimated 443-664 million doses would be required. In non-endemic countries, travelers could use an estimated 59-89 million vaccine doses, although the present product profile would make it unlikely to be able to administer vaccine in a timely manner.

METHODS

Calculations were based on 2015-2020 population projections for endemic countries in Asia and the Americas with populations >100,000. For dengue-endemic countries we assumed country-wide routine 12-23 month-old vaccination and catch-up vaccination among 2-14 year-old children employing a 2 or 3-dose schedule. Assumptions on expected vaccination coverage were based on country-specific public, private and travelers' sectors immunization performance.

CONCLUSIONS

Our results project an upper-limit estimate of vaccine demand, with actual demand depending on country priorities, cost and product profile. Given the potential for a dengue vaccine, policymakers in endemic and nonendemic countries should consider appropriate implementation strategies in advance of licensure.

Phylogeography of recently emerged DENV-2 in southern Viet Nam

Revealing the dispersal of dengue viruses (DENV) in time and space is central to understanding their epidemiology. However, the processes that shape DENV transmission patterns at the scale of local populations are not well understood, particularly the impact of such factors as human population movement and urbanization. Herein, we investigated trends in the spatial dynamics of DENV-2 transmission in the highly endemic setting of southern Viet Nam. Through a phylogeographic analysis of 168 full-length DENV-2 genome sequences obtained from hospitalized dengue cases from 10 provinces in southern Viet Nam, we reveal substantial genetic diversity in both urban and rural areas, with multiple lineages identified in individual provinces within a single season, and indicative of frequent viral migration among communities. Focusing on the recently introduced Asian I genotype, we observed particularly high rates of viral exchange between adjacent geographic areas, and between Ho Chi Minh City, the primary urban center of this region, and populations across southern Viet Nam. Within Ho Chi Minh City, patterns of DENV movement appear consistent with a gravity model of virus dispersal, with viruses traveling across a gradient of population density. Overall, our analysis suggests that Ho Chi Minh City may act as a source population for the dispersal of DENV across southern Viet Nam, and provides further evidence that urban areas of Southeast Asia play a primary role in DENV transmission. However, these data also indicate that more rural areas are also capable of maintaining virus populations and hence fueling DENV evolution over multiple seasons.

Dengue virus (DENV) is the cause of the most common vector-borne viral disease of humans, and is at particularly high prevalence in parts of Southeast Asia. Most studies of DENV transmission have focused on very local or international movement patterns, and have not explored how DENV moves through an endemic region. To address this issue, we employed newly developed phylogeographic methods to study patterns of spatial spread in 168 full-length DENV-2 genome sequences collected during a hospital-based study in southern Viet Nam, focusing on the Asian I genotype that recently emerged in this region. This analysis revealed that the urban population of Ho Chi Minh City plays a central role in the dispersal of the virus, and that DENV in this city tends to move along a gradient of population density. In addition, human movement between urban and rural areas was the most likely explanation for the rapid diffusion of DENV across southern Viet Nam following its introduction into Ho Chi Minh City. After reaching more rural areas, some virus lineages were maintained there for a number of years. These results therefore indicate that virological surveillance is necessary in both urban and rural populations.

Vector dynamics and transmission of dengue virus: implications for dengue surveillance and prevention strategies: vector dynamics and dengue prevention

Accounting for variation in mosquito vector populations will improve dengue surveillance and prevention. Because Aedes aegypti, the principle dengue virus (DENV) vector, transmit the virus with remarkable efficiency, entomological thresholds are especially low. Assessing risk of human infection based on immature mosquito indices has proven difficult. Greater emphasis should be placed on relative abundance of adult vectors in relation to human serotype-specific herd immunity, introduction of unique viruses, mosquito-human contact and weather. The most appropriate spatial scale for assessing entomological risk is the individual household. The scale for measuring DENV transmission risk has yet to be determined but is clearly larger than the household and likely to exceed several city blocks. Because households are expected to be a primary site for human DENV infection, intradomicile vector control strategies should be a priority, especially when the force of transmission is high. The most effective intervention strategy will combine vector control with vaccine delivery for rapid and sustained disease prevention.

Pupal sampling for Aedes aegypti (L.) surveillance and potential stratification of dengue high-risk areas in Cambodia

OBJECTIVES

To identify and describe the distribution of dengue vectors and factors affecting this distribution in Cambodia, with a view to practicing rational, evidence-based dengue outbreak prevention activities.

METHODS

Entomological survey with a questionnaire component in 100 randomly selected households in each of 13 clusters of high or low human population density of seven Cambodian provinces. Entomological and other indices were calculated, and statistical methods used to describe factors of potential outbreak risk.

RESULTS

Aedes aegypti was the principle dengue vector in all clusters, making up 95.5% (20,555 of 21,325) of the Aedes pupae population. The majority of pupae were recovered either from large concrete water storage jars (16,230; 76.1%) or concrete water storage tanks (2819; 13.2%). There were small but significantly higher levels of dengue vector infestation in rural than urban areas. The mean pupae density over the survey was 16.4/house, which ranged between clusters from 5.2/house to 56.9/house. The 'pupae-per-person' index was 2.4 and 3.6 in urban and rural areas, respectively, and was independent of mean human population density or household water container distribution.

CONCLUSIONS

High populations of household-associated dengue vectors were present in all surveyed clusters. The highly skewed distribution of pupae in a limited number of key containers suggests adoption and further development of community-based control measures targeting these containers holds most potential chance of controlling dengue outbreaks in Cambodia.

The effect of long-lasting insecticidal water container covers on field populations of Aedes aegypti (L.) mosquitoes in Cambodia

Dengue in Cambodia is mainly transmitted by Aedes aegypti (L.) mosquitoes that primarily breed in large, concrete jars (> or =200 liters) used for the storage of water for domestic use. Following a preliminary risk assessment, long-lasting insecticidal netting (LN) treated with deltamethrin was incorporated into the design of the covers for these jars. Their effect on immature and adult female populations of Ae. aegypti in six villages in a peri-urban area of Cambodia were compared with populations in six nearby control villages before and for 22 weeks after distribution of the jar covers. There were significantly fewer pupae per house in intervention villages than in control villages (6.6 and 31.9, respectively, p<0.01). Fewer pupae were recovered from intervention houses than from control houses at every post-intervention assessment. Two weeks after the intervention, the average number of indoor resting female Ae. aegypti per house in the intervention villages had declined approximately three-fold, whereas in the controls there was only a slight reduction (16%). The magnitude of the difference between the two areas diminished over time, which contact bioassays confirmed was likely due to a gradual reduction of insecticidal effect of the jar covers. In the study area, insecticide-treated covers for large concrete water storage jars were efficacious for controlling Ae. aegypti in the protected water jars and with a demonstrable effect on adult densities and survival. Further studies of this targeted container strategy in Cambodia, and elsewhere, are recommended. However, improvements in technology that would extend the duration of insecticidal effectiveness of LN materials may be needed for the development of cost-effective public health applications.

"Guidelines for the clinical evaluation of dengue vaccines in endemic areas": summary of a World Health Organization Technical Consultation

There is a pressing need for guidelines focused on the clinical evaluation of dengue vaccines in exposed populations, because Phase 1 and 2 clinical trials of dengue vaccines have begun, and Phase 3 field trials may be warranted soon. In response to this need, the WHO Initiative for Vaccine Research (IVR) has conducted a series of expert consultations resulting in guidelines published as a WHO; 2008[Report No.: WHO/IVB/08.12]. This document, directed toward national regulatory authorities (NRAs), vaccine developers and the scientific community at large, provides guidance for the evaluation and registration of dengue vaccines in dengue-endemic countries. The new document builds on a previous guidance document published in 2002 [WHO. Guidelines for the evaluation of dengue vaccines in populations exposed to natural infection. Geneva, Switzerland: WHO; 2002 [Report No.: TDR/IVR/DEN/02.1]]. This report summarizes the recommendations in the new guidelines, which emphasize the many unique aspects of dengue vaccine trials. These include strong recommendations to collect accurate dengue incidence data across multiple transmission seasons, and to conduct Phase 2 or 3 bridging studies, post-Phase 3 follow-up safety studies and Phase 4 post-licensure trials to better elucidate vaccine immunogenicity, protective efficacy, or safety in endemic areas where multiple dengue types and other flaviviruses circulate and where flavivirus vaccines are widely used.

The demand for a dengue vaccine: a contingent valuation survey in Metro Manila

Using data gathered from a contingent valuation survey, this study estimated the willingness to pay (WTP) for a single dengue fever vaccine and the household demand function for dengue vaccines. Mean WTP for the vaccine ranged from US$27 to US$32 and household demand averaged 2 per household. Our findings indicate sufficiently high WTP for dengue vaccines and hence a significant potential for selling the vaccine in private markets. For the lower income groups with lower capacity to pay, a mass vaccination campaign program in which part of the financial costs are covered by vaccine user charges is viable.

Community and school-based health education for dengue control in rural Cambodia: a process evaluation

Dengue fever continues to be a major public health problem in Cambodia, with significant impact on children. Health education is a major means for prevention and control of the National Dengue Control Program (NDCP), and is delivered to communities and in schools. Drawing on data collected in 2003–2004 as part of an ethnographic study conducted in eastern Cambodia, we explore the approaches used in health education and their effectiveness to control dengue. Community health education is provided through health centre outreach activities and campaigns of the NDCP, but is not systematically evaluated, is under-funded and delivered irregularly; school-based education is restricted in terms of time and lacks follow-up in terms of practical activities for prevention and control. As a result, adherence is partial. We suggest the need for sustained routine education for dengue prevention and control, and the need for approaches to ensure the translation of knowledge into practice.

Health education is essential for the control of diseases such as dengue, ensuring that community members understand the mechanisms of infection and the key behaviours or activities that need to be addressed to prevent transmission, reduce severe disease and avoid fatalities. In Cambodia, health education for dengue control is provided in primary schools, at village health centres and by the National Dengue Control Program. However, these educational programs are accorded low priority, strategies and materials are not evaluated on a routine basis, messages are sometimes confusing, and health staff and teachers lack the training, time and opportunities to deliver educational messages. Recommendations to villages are not always practical or effective in preventing mosquito bites, and funds are not available to provide new educational materials. While school children and their parents therefore have some familiarity with the behaviour and habitat of the aedes mosquito and the environmental factors that contribute to dengue fever, their knowledge is uneven and knowledge is rarely translated to reduce the risk of infection. Community involvement in the prevention and control of dengue is essential, but will not be effective while health education is poorly resourced and irregular and lessons on prevention do not result in action.

Cost-effectiveness of annual targeted larviciding campaigns in Cambodia against the dengue vector Aedes aegypti

OBJECTIVE

To assess the cost-effectiveness (CE) of annual targeted larviciding campaigns from 2001 to 2005 against the dengue vector Aedes aegypti in two urban areas of Cambodia with a population of 2.9 million people.

METHODS

The intervention under analysis consisted of annual larviciding campaigns targeting medium to large water storage containers in households and other premises. The CE compared the intervention against the hypothetical alternative of no intervention. The CE was calculated as the ratio of disability adjusted life years (DALYs) saved to the net cost of the intervention (in 2005 US dollars) by year. A sensitivity analysis explored the range of study parameters.

RESULTS

The intervention reduced the number of dengue cases and deaths by 53%. It averted an annual average of 2980 dengue hospitalizations, 11,921 dengue ambulatory cases and 23 dengue deaths, resulting in a saving of 997 DALYs per year. The gross cost of the intervention was US $567,800 per year, or US $0.20 per person covered. As the intervention averted considerable medical care, the annual net cost of the intervention was US $312,214 (US $0.11 per person covered) from a public sector perspective and US $37,137 (US $0.01 per person covered) from a societal perspective. The resulting CE ratios were: US $313/DALY gained from the public perspective and US $37/DALY gained from the societal perspective. Even under the most conservative assumption, the intervention remained cost effective from both perspectives.

CONCLUSIONS

Annual, targeted larviciding campaigns appear to have been effective and cost-effective medium-term interventions to reduce the epidemiologic and economic burden of dengue in urban areas of Cambodia.

Dengue vaccines approach the finish line

The spread of dengue virus (DV) via its Aedes mosquito vector throughout most of the tropics has led to a worldwide resurgence of epidemic dengue, including dengue hemorrhagic fever. For the first time in 60 years, the pipeline of dengue vaccines looks promising. Strains of each of the 4 DV serotypes, attenuated by passage in tissue culture or by recombinant DNA technology, have been formulated into tetravalent vaccines and have entered successful phase 1 and 2 clinical trials in the United States and Southeast Asia. Antibody-dependent enhancement of wild-type DV infections by the vaccine represents a unique safety issue, which is under investigation. The Pediatric Dengue Vaccine Initiative (funded by the Bill and Melinda Gates Foundation), the World Health Organization, industry, the US military, and governments of tropical countries are collaborating to accelerate dengue vaccine development and phase 3 vaccine efficacy trials in countries where dengue is endemic. A protective tetravalent vaccine must be licensed soon if dengue is to be brought under control.

Burden of symptomatic dengue infection in children at primary school in Thailand: a prospective study

BACKGROUND

Dengue viruses are a major cause of morbidity and mortality in tropical and subtropical areas. Our aim was to assess prospectively the burden of dengue-related illness in children in Thailand.

METHODS

We did a prospective study in a cohort of children at primary school in northern Thailand from 1998 to 2002. We assessed the burden of dengue illness as disability-adjusted life years (DALYs) and patient costs per illness.

FINDINGS

Dengue accounted for 328 (11%) of the 3056 febrile cases identified in 2114 children during the study period. The mean burden of dengue was 465.3 (SD 358.0; range 76.5-954.0) DALYs per million population per year, accounting for about 15% of DALYs lost to all febrile illnesses (3213.1 [SD 2624.2] DALYs per million per year). Non-hospitalised patients with dengue illnesses represented a substantial proportion of the overall burden of disease, with 44-73% of the total DALYs lost to dengue each year due to such illness. The infecting dengue serotype was an important determinant of DALYs lost: DEN4 was responsible for 1% of total DALYs lost, DEN1 for 9%, DEN2 for 30%, and DEN3 for 29%.

INTERPRETATION

Use of prospective data to estimate the burden of disease shows that most DALYs lost to dengue illness were the result of non-hospitalised illnesses of long duration. Thus, inclusion of non-hospitalised cases is critical to accurately assess the total burden of dengue illness.

Dengue virus infection: a major cause of acute hepatic failure in Thai children

BACKGROUND

Acute hepatic failure (AHF) can be caused by a variety of viruses, drugs, toxins and metabolic disorders.

AIMS

A prospective study was conducted to determine the aetiology and outcome of AHF in Thai children aged 1-15 years.

METHODS

All serum samples were tested for anti-HAV IgM, HBsAg, anti-HBc IgM, anti-HCV, anti-HEV IgM and anti-dengue IgG and IgM. Further individual investigations were done according to the clinical impression.

RESULTS

Forty subjects were enrolled from 14 centres during February 2000 to December 2001. Five cases were excluded owing to a lack of evidence of encephalopathy. The causes of AHF were dengue infection in 12 (34.3%), Wilson disease in 2 (5.7%), T-cell lymphoma in 2 (5.7%), ischaemic hepatitis in two (5.7%), haemophagocytic syndrome in one (2.8%), CMV in 2 (5.7%), Reye syndrome in one (2.8%) and unknown in 13 (37.1%) patients. The fatality rate was 68.6%. Eight of 24 (33.3%) deaths were caused by dengue infection.

CONCLUSIONS

Improvements in sanitation and socio-economic status as well as the implementation of hepatitis B vaccine in the Extended Programme on Immunization (EPI) are likely to be the reasons for the observed absence of AHF caused by hepatitis A and B. The study showed that dengue infection, on the other hand, was a major cause of AHF in Thailand.

Periodic and aperiodic traveling pulses in population dynamics: an example from the occurrence of epidemic infections

The dynamics of the occurrence of the dengue hemorrhagic fever in the 72 provinces of Thailand is investigated by performing a proper orthogonal decomposition (POD) on spatiotemporal data. Using this technique, we are able to identify and select the contribution of different modes, selected according to the energy content, to the evolution of the epidemic during 14 years. We found that the phenomenon is characterized by periodic cycles of yearly occurrence characterized by spatial scales of about 420 km. Superimposed on this basic mode, POD analysis is able to reveal the presence of high-energetic aperiodic traveling pulses of the epidemic, which extend spatially for about 510 km from Bangkok.

A web-based multimedia spatial information system to document Aedes aegypti breeding sites and dengue fever risk along the US-Mexico border

This paper describes a web-based multimedia spatial information system used to support a study of the re-invasion of Aedes aegypti, the mosquito vector for dengue fever, in the deserts of the southwest United States/northwest Mexico. The system was developed applying Open Geospatial Consortium and World Wide Web Consortium Open Specifications and using Open Source Software. The system creates a sensory-rich environment, one which allows users to interact with the system to explore connections among data (maps, remotely sensed images, text, graphs, 360 degree panoramas and photos), visualize information, formulate their own interpretations, generate hypotheses and reach their own conclusions.

Randomized, placebo-controlled trial of nonpegylated and pegylated forms of recombinant human alpha interferon 2a for suppression of dengue virus viremia in rhesus monkeys

Dengue fever and dengue hemorrhagic fever are caused by infection with any one of the four dengue viruses (DVs) and are significant public health burdens throughout the tropics. Higher viremia levels are associated with greater dengue disease severity. A therapeutic intervention to suppress viremia early in DV infection could potentially ameliorate severe disease. Recombinant alpha interferon 2a (rIFN-alpha-2a, Roferon-A) suppressed DV replication in human peripheral blood mononuclear cells in vitro. We therefore examined the effects of rIFN-alpha-2a and pegylated recombinant IFN-alpha-2a (PEG-rIFN-alpha-2a, PEGASYS) on DV serotype 2 (DV-2) viremia in rhesus monkeys. Flavivirus-naïve monkeys were inoculated with DV-2 and randomized to receive a single dose of rIFN-alpha-2a (10 million international units/m2) versus placebo or PEG-rIFN-alpha-2a (6 microg/kg) versus placebo 1 day after the onset of viremia. Serial daily viremia levels were measured, and convalescent-phase DV-2 neutralizing antibody titers were determined. Compared to placebo, a single injection of rIFN-alpha-2a temporarily suppressed DV-2 replication and delayed the time to peak viremia by a median of 3 days. However, measures of total viral burden were not different between the two groups. A single injection of PEG-rIFN-alpha-2a significantly lowered daily viremia levels and improved virus clearance, starting 48 h after administration. There were no significant differences in DV-2 neutralizing antibody titers between the treatment and placebo groups at 30 and 90 days postinfection. Based on their individual effects, future studies should investigate a combination of rIFN-alpha-2a and PEG-rIFN-alpha-2a for suppression of dengue virus viremia and as a potential therapeutic intervention.

Policymakers' views regarding the introduction of new-generation vaccines against typhoid fever, shigellosis and cholera in Asia

Face-to-face interviews and meetings with more than 160 policymakers and other influential professionals in seven large Asian countries (Bangladesh, China, India, Indonesia, Pakistan, Thailand and Vietnam) were conducted to survey opinions regarding the need for, and potential uses of new-generation vaccines against cholera, typhoid fever and shigellosis. Despite several barriers to their uptake--notably uncertainty of the burden of enteric diseases; preference for water, sanitation and other environmental improvements over vaccination for disease control; and high prices of the current vaccines relative to basic EPI vaccines, and their moderate protection levels--considerable interest was found in the targeted use of Vi typhoid vaccine in most countries, followed by (future) Shigella and oral cholera vaccines. The introduction of these vaccines in Asia could be greatly facilitated by country-specific evidence of disease burden, local or regional vaccine production, field studies demonstrating their safety and efficacy in local populations, evidence of potential economic savings from vaccination, and effective dissemination of research results to all those who make or influence immunization policy.