Herd immunity halts cholera in unvaccinated population in Zanzibar, study shows

On the Tanzanian island of Zanzibar, some individuals may not even need a vaccine to protect them against cholera. Research shows herd immunity has helped guard against the disease in sub-Saharan Africa.

To test the theory, nearly 24,000 people there received two doses of an oral cholera vaccine. After a cholera outbreak in 2009-2010, researchers found that not only was the vaccine 79% protective in those who received it, but also that those who did not saw their risk of infection decrease, according to the study abstract.

"Our findings suggest that the oral cholera vaccine offers both direct and indirect (herd) protection in a sub-Saharan African setting," the study authors write. "Mass oral cholera [immunization] campaigns have the potential to provide not only protection for vaccinated individuals but also for the unvaccinated members of the community and should be strongly considered for wider use."

Cholera is a potentially fatal intestinal infection that occurs after ingesting food or water with Vibrio cholerae bacterium. The World Health Organization (WHO) says the disease poses a global threat, due to its high incidence in countries with poor hygienic and sanitary standards. But as WHO and drug manufacturers beef up on cholera vaccine production, as NPR reports, fewer individuals may need to get vaccinated than previously thought, thanks to the herd immunity phenomenon.

More findings can be found in the journal The Lancet Infectious Diseases.

- check out the study abstract
- here's NPR's take