Kok Ben Toh

Northwestern University | NU · Department of Preventive Medicine

Background In the context of high malaria burden yet limited resources, Guinea's national malaria program adopted an innovative subnational tailoring (SNT) approach, including engagement of stakeholders, data review, and data analytics, to update their malaria operational plan for 2024-2026 and identify the most appropriate interventions for each d...

We evaluate approaches to vaccine distribution using an agent-based model of human activity and COVID-19 transmission calibrated to detailed trends in cases, hospitalizations, deaths, seroprevalence, and vaccine breakthrough infections in Florida, USA. We compare the incremental effectiveness for four different distribution strategies at four diffe...

The onset of the COVID-19 pandemic drove a widespread, often uncoordinated effort by research groups to develop mathematical models of SARS-CoV-2 to study its spread and inform control efforts. The urgent demand for insight at the outset of the pandemic meant early models were typically either simple or repurposed from existing research agendas. Ou...

Epidemic data are often difficult to interpret due to inconsistent detection and reporting. As these data are critically relied upon to inform policy and epidemic projections, understanding reporting trends is similarly important. Early reporting of the COVID-19 pandemic in particular is complicated, due to changing diagnostic and testing protocols...

Our ability to forecast epidemics far into the future is constrained by the many complexities of disease systems. Realistic longer-term projections may, however, be possible under well-defined scenarios that specify the future state of critical epidemic drivers. Since December 2020, the U.S. COVID-19 Scenario Modeling Hub (SMH) has convened multipl...

Droughts are linked to tree die-offs in the biodiverse humid tropics. We assessed drought response of a Dipterocarp Forest and found a marginal decrease in tree survival, indicating drought resistance. Understory and emergent species were sensitive to drought. Urgent focus is needed to understand drought impacts and plant physiological responses in...

Our ability to forecast epidemics more than a few weeks into the future is constrained by the complexity of disease systems, our limited ability to measure the current state of an epidemic, and uncertainties in how human action will affect transmission. Realistic longer-term projections (spanning more than a few weeks) may, however, be possible und...

The onset of the COVID-19 pandemic drove a widespread, often uncoordinated effort by research groups to develop mathematical models of SARS-CoV-2 to study its spread and inform control efforts. The urgent demand for insight at the outset of the pandemic meant early models were typically either simple or repurposed from existing research agendas. Ou...

Epidemiological models must be calibrated to ground truth for downstream tasks such as producing forward projections or running what-if scenarios. The meaning of calibration changes in case of a stochastic model since output from such a model is generally described via an ensemble or a distribution. Each member of the ensemble is usually mapped to...

Background Decision-makers impose COVID-19 mitigations based on public health indicators such as reported cases, which are sensitive to fluctuations in supply and demand for diagnostic testing, and hospital admissions, which lag infections by up to two weeks. Imposing mitigations too early has unnecessary economic costs while imposing too late lead...

Policymakers must make management decisions despite incomplete knowledge and conflicting model projections. Little guidance exists for the rapid, representative, and unbiased collection of policy-relevant scientific input from independent modeling teams. Integrating approaches from decision analysis, expert judgment, and model aggregation, we conve...

Background: A recent WHO recommendation for perennial malaria chemoprevention (PMC) encourages countries to adapt dose timing and number to local conditions. However, knowledge gaps on the epidemiological impact of PMC and possible combination with the malaria vaccine RTS,S hinder informed policy decisions in countries where malaria burden in youn...

Background: A recent WHO recommendation for perennial malaria chemoprevention (PMC) encourages countries to adapt dose timing and number to local conditions. However, knowledge gaps on the epidemiological impact of PMC and possible combination with the malaria vaccine RTS,S hinder informed policy decisions in countries where malaria burden in young...

We evaluate approaches to vaccine distribution using an agent-based model of human activity and COVID-19 transmission calibrated to detailed trends in cases, hospitalizations, deaths, seroprevalence, and vaccine breakthrough infections in Florida, USA. We compare the incremental effectiveness for four different distribution strategies at four diffe...

Coral restoration has largely focused on improving techniques and biological yield to hasten reef recovery. However, as socioeconomic considerations can affect restoration success, it is important to also consider inputs from various stakeholders in the design and execution of restoration projects. Through online questionnaires, the knowledge level...

The global biodiversity crisis is escalating rapidly, with nearly a million species facing extinction risk in the near future. Monitoring of Essential Biodiversity Variables (EBV; key variables measured to detect changes in biodiversity) over time is important for biodiversity conservation, which in turn necessitates baseline estimates of EBVs. Usi...

Background Decision-makers impose COVID-19 mitigations based on public health indicators such as reported cases, which are sensitive to fluctuations in supply and demand for diagnostic testing, and hospital admissions, which lag infections by up to two weeks. Imposing mitigations too early has unnecessary economic costs, while imposing too late lea...

Background Access to healthcare is important in controlling malaria burden and, as a result, distance or travel time to health facilities is often a significant predictor in modelling malaria prevalence. Adding new health facilities may reduce overall travel time to health facilities and may decrease malaria transmission. To help guide local decisi...

Riparian forests are ecotones that link aquatic and terrestrial habitats, providing ecosystem services including sediment control and nutrient regulation. Riparian forest function is intimately linked to river hydrology and floodplain dynamics, which can be severely altered by dams. The Tocantins River in the eastern Amazon has six mega-dams along...

Music and empathy are components of social experience. Similar and adjacent functional brain systems are required in the production and understanding of music, the processing of emotion, and engagement in social behavior. Activity in these brain systems is often reflected in autonomic features, including dynamic behavior of the parasympathetic and...

Obtaining accurate population counts of endangered species is central to conservation biology, with implications for gaining ecological insights, informing management strategies, and judicial use of conservation funds. Despite decades of progress in methodological developments in the realm of population ecology, reliable density estimates are unava...

Background: Access to healthcare is important in controlling malaria burden and, as a result, distance or travel time to health facilities is often a significant predictor in modeling malaria prevalence. Adding new health facilities may reduce overall travel time to health facilities and may decrease malaria transmission. To help guide local decisi...

The most common approach to create spatial prediction of malaria in the literature is to approximate a Gaussian process model using stochastic partial differential equation (SPDE). We compared SPDE to computationally faster alternatives, generalized additive model (GAM) and state-of-the-art machine learning method gradient boosted trees (GBM), with...

Policymakers make decisions about COVID-19 management in the face of considerable uncertainty. We convened multiple modeling teams to evaluate reopening strategies for a mid-sized county in the United States, in a novel process designed to fully express scientific uncertainty while reducing linguistic uncertainty and cognitive biases. For the scena...

This work is currently under review for publication.

Background: Mass drug administration and mass-screen-and-treat interventions have been used to interrupt malaria transmission and reduce burden in sub-Saharan Africa. Determining which strategy will reduce costs is an important challenge for implementers; however, model-based simulations and field studies have yet to develop consensus guidelines....

Predicting the bleaching responses of corals is crucial in light of frequent heat stress events to manage further losses of biodiversity and ecosystem functioning, especially for reefs impacted by urbanisation. We examined if the coral cover and community at various Singapore sites changed during the 2016 global coral bleaching event. Bleaching pre...

Significance Using realistic simulation of dengue and plausible control programs in the state of Yucatán, Mexico, we show that vaccination programs can have amplifying or interfering dynamic effects when combined with expanded vector control effort. These results should inform planning in regions considering an integrated dengue control program, pa...

The establishment of marinas alters physico-chemical conditions and affects distribution of resident epibiotic and pelagic communities along coastal areas. However, information on the soft bottom macrobenthos within and around these boating facilities in the tropics is limited. Here, we investigated if macrobenthic communities differed among three...

Geospatial statistical models play an important role in malaria control and prevention; they are widely used to produce malaria risk maps, which are essential to guide efficient resource allocation for intervention. Although many models are available for spatial mapping, the most commonly used model in the literature is the Bayesian geostatistical...

Article impact statement: Web‐app development frameworks enable the creation of decision‐support tool prototypes for actionable conservation science. This article is protected by copyright. All rights reserved

Count data commonly arise in natural sciences but adequately modeling these data is challenging due to zero-inflation and over-dispersion. While multiple parametric modeling approaches have been proposed, unfortunately there is no consensus regarding how to choose the best model. In this article, we propose a ordinal regression model (MN) as a defa...

The ratio of barium to calcium in coral skeletons (Ba/Ca coral ) is broadly used as a proxy for tracking terrestrial/river runoff. There are, however, inconsistencies in Ba/Ca coral records that have prompted caution in its reliability as an environmental proxy. Direct comparisons between in-situ seawater measurements and coral Ba/Ca are therefore...

Rapid coastal development has generated interest in the ecology of human-modified marine environments. Coastal defence structures such as breakwaters and seawalls are increasingly built to reduce erosion and to mitigate the impacts of sea level rise but knowledge on the marine biodiversity around these structures is lacking. Benthic cover and fish...

The recovery of bleached corals is crucial in ensuring the persistence of the coral reef ecosystem function. This study investigated whether relocating bleached Platygyra sinensis colonies was a viable measure to accelerate their recovery. During a mild bleaching event in 2014, eight bleached colonies of P. sinensis were relocated from an affected...

Transplanting nursery-reared corals is among one of the most common approaches to assist the recovery of degraded reefs. The nursery phase is considered essential for providing a favourable environment for coral fragments to grow into suitable sizes before transplantation to natural reef substrates. Several types of coral nursery designs have been...

Camouflage is a key predation prevention mechanism. The most intuitive camouflage strategy is background matching, where a prey resembles the colour and pattern of its background. Spots (e.g. geometric ‘elements’ that constitute a pattern) are a common feature on the body of prey, but the effect of their size in relation to elements in the backgrou...

In situ nurseries have been a crucial part of coral reef restoration initiatives for the past two decades. However, the advantages over direct transplantation in sedimented waters has yet to be examined. In the present study, we showed that Pachyseris speciosa and Pocillopora damicornis fragments reared in in situ nurseries (NR) in Singapore’s sedi...

Berthing pontoons, one of the most ubiquitous structures in marinas, are known to provide recruitment substrate for a variety of marine biota but little has been reported on their capacity to support epibiotic organisms in tropical marinas, and even less is known about the factors that shape their distribution in such environments. We surveyed the...

Seawalls, which have replaced many natural shorelines in coastal cities, are increasingly built to alleviate the impacts of rising sea levels. To mitigate the consequential loss of biodiversity, novel approaches such as ecological engineering have been adopted to enhance the biodiversity on these artificial structures. However, the majority of rese...

Coral bleaching events have been predicted to occur more frequently in the coming decades with global warming. The susceptibility of corals to bleaching during thermal stress episodes is dependent on many factors and an understanding of these underlying drivers is crucial for conservation management. In 2013, a mild bleaching episode ensued in resp...

Bleaching response among sites and genera. Total number of corals recorded in all seven sites and the corresponding bleaching prevalence for each genera (SS = Sultan Shoal). (PDF)

Singapore’s coastal environment has been extensively transformed by numerous development projects since the 1960s. However, fish diversity remains relatively high despite the extent of anthropogenic modifications to these environments. The diversity and abundance of fishes supported by recreational marinas in Singapore was examined in this study. C...

The octocoral Heliopora coerulea is a gonochoric surface brooder. Although the species is common on shallow Indo-Pacific coral reefs, information on its reproductive biology is limited and spawning timings have only been reported from four locations. We report the first observations of surface brooding in H. coerulea on a sedimented equatorial reef...

Interactions between disruptive colouration and the match between prey and background spot size were manipulated in two experiments that used time taken by human ‘predators’ to find artificial prey (virtual crab morphs) against heterogeneous backgrounds as a measure of the their camouflage. Experiment 1, in which the spots and their placement imita...

Most of Singapore's coastline has been modified by coastal development with variable influences on marine biodiversity. Marinas are typically designed as a semi-enclosed environment with a complex mix of structures that provide ecological niches throughout the water body. Water flow is inevitably reduced with a possible decline of water quality. Th...

Size-dependant mortality influences the recolonization success of juvenile corals transplanted for reef restoration and assisting juvenile corals attain a refuge size would thus improve post-transplantation survivorship. To explore colony size augmentation strategies, recruits of the scleractinian coral Pocillopora damicornis were fed with live Art...

Dense aggregations of a cucumariid sea cucumber were first observed in December 2012 on a sedimented coral reef at Sultan Shoal (1°14’22.40”N, 103°38’53.06”E), a small coral-fringed island south of mainland Singapore (Fig. 1a). Individuals of 3–4 cm length were found tightly nested on rocks (Fig. 1b), rubble, and the underside and dead sections of...

The dietary habits of the sea urchin Salmacis sphaeroides and the gastropod Trochus maculatus in ex situ mariculture were examined. Fouling algal assemblages on terracotta tiles were exposed to the grazers and compared. Except for Day 0, the assemblages on Days 2, 13 and 27 differed significantly across treatments. S. sphaeroides rapidly consumed m...

Climate change impacts are expected to impose further challenges to the management of the coastal and marine environment. The island nation of Singapore has lost 96% of its mangroves and 60% of its coral reefs to coastal development and maintaining the remaining existing habitats is crucial. Two recent extreme climatic events in Singapore provide i...

We compared diversity of marine invertebrates along mid-reef, reef crest and reef slope regions in the coral reef at Tunku Abdul Rahman marine sanctuary at Gaya Island in Sabah, Malaysia. 12 plots were placed in 4 replications in each marine zonation. The most diversity in marine invertebrates was found in the reef crest area, possibly because this...

We investigated the frog call intensity in two anthropogenic habitats at Maliau Basin Study Center premises. Two species, Rana nicobariensis and Bufo juxtasper dominated the two sites. The calling intensity of the studied frog communities peaked at 2200hrs. Bufo juxtasper tend to call more often under rainy conditions. In the presence of more calli...