Herd immunity conferred by killed oral cholera vaccines in Bangladesh: a reanalysis

This article, published in the Lancet, reports on a study in Bangladesh to ascertain whether cholera vaccines can create “herd immunity” – protecting non-vaccinated individuals from the disease as well as those who are vaccinated. The study found that high levels of vaccine coverage were linked to a reduced risk of cholera both in individuals who received a placebo, and in those who received the vaccine. There is evidence that in Bangladesh, individuals who have been vaccinated, as well as being less likely to become infected with cholera, are also less likely to pass on the disease if they do become infected. The article suggests that this may explain why herd immunity occurs.

The article concludes that, in addition to providing direct protection to vaccine recipients, cholera vaccines confer significant indirect protection to neighbouring non-vaccinated individuals. In addition, progressively higher levels of vaccine coverage can lead to increasing levels of indirect protection. The findings suggest that substantial levels of indirect protection, in addition to direct protection, could be attained in public-health programmes that deploy these vaccines. This reinforces recent World Health Organization recommendations which suggest that vaccines should be reconsidered as measures for the control of cholera.