Survivors of severe cholera infections receive long-lasting immunity
to reinfection. The significance of this immunity for epidemiology is unclear,
however, due to the large fraction of cholera cases that are mild or
asymptomatic. We analyzed 50 yr of cholera mortality data from 26 districts
in historic Bengal using mechanistic, continuous-time Markov chain models and
brand-new likelihood inference techniques. Our models fit the data
dramatically better than all previously presented models and robustly predict
that most exposures result not in infection but in short-term immunity, which
wanes on a timescale of a few weeks. Our results afford a view of cholera
dynamics very different from that presently prevailing and suggest a new
focus for future investigations of cholera immunology and control.
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