The Role of Vaccine Coverage within Social Networks in Cholera Vaccine Efficacy

Abstract

BackgroundTraditional vaccine trial methods have an underlying assumption that the effect of a vaccine is the same throughout the trial area. There are, however, many spatial and behavioral factors that alter the rates of contact among infectious and susceptible individuals and result in different efficacies across a population. We reanalyzed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from cholera vaccines when vaccination rates are high in an individual's social network.MethodsWe analyzed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse trend for the relation between the level of vaccine coverage in an individual's social network and the incidence of cholera in individual vaccine recipients or placebo recipients after controlling for potential confounding variables.ResultsUsing bari-level social network ties, we found incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (5.28 cases per 1000 in the lowest quintile vs 3.27 cases per 1000 in the highest quintile; p = 0.037 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's social network were independently related to a reduced risk of cholera.ConclusionsFindings indicate that progressively higher levels of vaccine coverage in bari-level social networks can lead to increasing levels of indirect protection of non-vaccinated individuals and could also lead to progressively higher levels of total protection of vaccine recipients.

Assessing effects of cholera vaccination in the presence of interference

“…The Matlab cholera vaccine trial analysis presented in this paper extends previous association-type analyses of population-level vaccine efficacy (Ali et al 2005, 2009; Root et al 2011) to inference about the different causal effects of the vaccine(s). Such inference quantifies the expected number of cholera cases prevented for different levels of vaccine coverage in both vaccinated and unvaccinated individuals, providing clearer interpretation of and additional insight into the population-level impact of vaccination for investigators and policy makers.…”

“…These results suggest possible interference between individuals in spatial proximity to one another. Similarly, Root et al (2011) found that incidence of cholera among placebo recipients declined with increasing vaccine coverage within an individual’s kinship network.…”

Randomization inference with general interference and censoring

“…Likewise, Root et al . () concluded that the risk of cholera among placebo recipients was inversely associated with level of vaccine coverage in their social networks. Motivated by these association analyses, Perez‐Heydrich et al .…”

“…Following Root et al . (), the third interference structure is defined according to a kinship‐based social network between baris. The Matlab Demographic Surveillance System recorded the exact dates and bari of residence over time for each individual.…”

“…The previous two specifications assume a local interference structure based on geographical location of individuals' households. Following Root et al (2011), the third interference structure is defined according to a kinship-based social network between baris. The Matlab Demographic Surveillance System recorded the exact dates and bari of residence over time for each individual.…”