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In February 2025, Drs. George and Namunesha published a report on cholera genomic epidemiology and vaccine effectiveness from a cholera surveillance project in eastern Democratic Republic of the Congo. During a four-year period (2020-2024), the team of investigators based at the Catholic University of Bukavu and the Ministry of Health in Bukavu studied 1,154 diarrhea patients,  including 342 patients with culture-confirmed cholera.   Whole genome sequencing on clinical and water V. cholerae isolates from 200 patient households showed that the clinical and water isolates from the same household were closely related, suggesting person-to-person and water-to-person transmission.  Because this area is known to be a high-risk area for cholera, the Ministry of Health had carried out a campaign to deliver over a million doses of oral cholera vaccine campaign to people in this area in 2022.  By determining which patients had received the vaccine, they found that a single dose of the vaccine reduced the risk of cholera by about 57%. Unfortunately, they also found that coverage of the vaccine was low, with only about 9% of the people having received the vaccine, so many of the people did not receive the vaccine in spite of the large number of doses delivered.  

This study provides several lessons for cholera control. These include the high risk for households of patients with cholera, so when treating an acutely ill cholera patient, one should also focus on preventing illnesses in the household and potentially in the immediate neighborhood.  These infections around the case may be the result of a common source, but some are likely caused when the patient transmits the Vibrio to others through fecal-oral spread.  Secondly, the oral cholera vaccine does reduce the risk of cholera, but to be truly effective, coverage rates must be much higher to achieve herd protection.  Unfortunately, the current global supply is not sufficient to provide a vaccine to all who need it. 

The study also points to the work ahead to understand how best to stop transmission in the high-risk areas, like Eastern Congo, and the high-micro-risk areas, like households and neighborhoods.  There is a need to focus on effective interventions to these hotspots and microhotspots. 

This paper was published in Emerging Infectious Diseases in February 2025, DOI: 10.3201/eid3102.241777.