Spillover effects

Spillover effects are the impacts interventions have on non-recipients that are connected to recipients through social or geographic proximity (i.e., “herd effects”, “indirect effects”). Interventions that produce spillover effects have a greater population-level health impact and higher cost-effectiveness than those that do not and thus may be more promising for infectious disease control and elimination. While spillover effects of vaccines have been estimated for decades, we have spearheaded research to extend methods of spillover estimation to other types of interventions. To learn more, see our systematic review and methods synthesis in the International Journal of Epidemiology and our article on spillover effects of WASH interventions in American Journal of Epidemiology.


In 2019, the Lancet Commission on malaria eradication called for a global effort to eradicate malaria worldwide by 2050, and several countries in southern Africa have set goals to eliminate malaria locally by 2030. In settings approaching malaria elimination, transmission is low, and cases cluster in geographic “hot spots”. We are investigating the effectiveness of reactive, focal chemotherapy and vector control interventions delivered in the neighborhood around malaria cases. The study will analyze data from three randomized trials in Namibia, Eswatini, and Zambia.

Soil-transmitted helminths

Though a large body of observational evidence suggests that WASH interventions can reduce soil-transmitted helminth (STH) incidence, few randomized trials have evaluated this question, and even fewer studies have used cutting edge diagnostics with high sensitivity and specificity. We have conducted both observational and randomized studies in Bangladesh to investigate whether water, sanitation, handwashing (WASH), and nutrition interventions reduce STH infections. In addition, we compared the performance of a new molecular STH diagnostic to the traditional microscopy-based approach. More recently, we have investigated whether finished household flooring (e.g., cement floors) is associated with lower STH and Giardia infection in young children in rural Bangladesh. To learn more, see our papers in PLoS NTDs papers on WASH and diagnostics and our Lancet Global Health paper on flooring.


School-located influenza vaccination programs have the potential to increase influenza vaccination among school-age children, who are responsible for the majority of influenza transmission. We are conducting an evaluation of Shoo the Flu, a city-wide program offering free influenza vaccination to elementary schoolchildren in Oakland, California since 2014. This evaluation is measuring the impact of Shoo the Flu on influenza vaccination coverage, influenza illness, influenza hospitalization, and school absenteeism. In addition to estimating impacts of the program on schoolchildren, we are measuring community-wide spillover effects. To learn more, see our papers in PLoS Medicine, Vaccine, and our medRxiv preprint.

Child growth

Children’s growth trajectories in early life influence their long-term health and development. In particular, stunting, a form of linear growth faltering, is associated with increased risk of illness, impaired cognitive development, and mortality. We conducted individual participant meta-analyses of over 35 longitudinal cohort studies of child growth from 15 low- and middle-income countries from 1990 to 2015. We found that the majority of stunting onset occurs from birth through 3 months of age, with lower incidence at later ages. Our findings suggest that prenatal, early postnatal, and possibly pre-conception interventions are needed to prevent most linear growth faltering. To learn more, see our preprints on stunting, wasting, and risk factors associated with child growth faltering.

Water quality

In the United States, recreating in coastal and inland water bodies may increase the risk of gastrointestinal illness due to fecal contamination of the water. Our research on recreational water quality aims to create evidence to support the establishment of policies including recreational water monitoring criteria that protect public health. We contributed to cohort studies of beachgoers to estimate the burden of illness associated with recreational water exposure across the United States and estimated associations with illness among surfers exposed to wet- vs. dry-weather conditions in southern California. We have also explored whether swimming in water where coliphages, a bacteriophage that infects E. coli, were associated with illness. This work has directly informed U.S. Environmental Protection Agency policies recommendations related to the use of coliphages as an indicator of viral water contamination.


Our research leverages data science tools to increase transparency and reproducibility in epidemiology. We regularly publish analysis datasets and replication scripts. The data science best practices for transparency and reproducibility are summarized in a lab manual, which our team is continuously updating. In addition, we have developed an internal replication process that increases reproducibility by identifying and resolving errors prior to publication.