This study aims at understanding the individual and community-level
characteristics that influenced par-ticipation in two consecutive
vaccine trials (typhoid and cholera) in urban slums of Kolkata, India.
The study area was divided into 80 geographic clusters (communities),
with 59, 533 subjects aged 65 2 years for analysis. A multi-level
model was employed in which the individuals were seen nested within the
cluster. Rates of participation in both the trials were nearly the
same; those who participated in the initial trial were likely to
participate in the subsequent cholera vaccine trial. Communities with
predominantly Hindu population, lower percentage of households with an
educated household head, or lower percentage of households owning a
motorbike had higher participation than their counterparts. At
individual scale, higher participation was observed among younger
subjects, females, and individuals from households with a household
head who had no or minimal education. Geographic patterns were also
observed in participa-tion in the trials. The results illustrated that
participation in the trial was mostly influenced by various indi-vidual
and community-level factors, which need to be addressed for a
successful vaccination campaign