Vaxchora shows high effectiveness against Mayotte cholera outbreak

A rapid, single-dose campaign using the live-attenuated oral cholera vaccine Vaxchora was associated with an estimated 87% effectiveness against cholera during the 2024 outbreak in Mayotte, according to a modelling study of the French Indian Ocean territory. Researchers focused on Koungou village, where the outbreak produced substantial transmission and vaccination reached 71% of the population considered at risk. The results indicate that the vaccine, formally known as CVD 103-HgR, can perform effectively under the demanding and time-sensitive conditions of a real-world outbreak, although the number of cases averted at population level was less certain.

The analysis used daily cholera case data separated by vaccination status to calibrate several stochastic models of disease transmission. At its baseline estimate, the model placed the basic reproduction number, R0, at 1.5, with a 95% credible interval of 1.2 to 1.9. This quantity describes how many secondary infections are generated by an infected person in a wholly susceptible population. A value above one indicates that an outbreak can expand without control measures, while the relatively modest estimate in Koungou is consistent with a setting in which transmission remained vulnerable to interruption through vaccination and other interventions.

The observational and modelling data covered 4,733 people deemed at risk in Koungou. Of these, 3,354 received CVD 103-HgR, representing 71% coverage. During the period from 19 April to 7 July 2024, 77 confirmed cholera cases were recorded with symptom onset in the analysed population. By comparing the epidemic trajectory among vaccinated and unvaccinated people, the investigators estimated that the vaccine prevented 87% of cholera cases at baseline. The 95% credible interval extended from 74% to 99%, indicating that even the lower bound represented substantial protection.

Those estimates remained comparatively stable when the researchers examined alternative assumptions in sensitivity analyses: vaccine effectiveness ranged from 75% to 91% across the scenarios considered. This robustness is important because real-world evaluations of outbreak vaccination are rarely as straightforward as controlled human challenge studies. Coverage may be uneven, doses may be administered at different times relative to exposure, people can move between areas, and other prevention measures may operate at the same time. The model attempted to account for these features by fitting multiple stochastic formulations to the observed case series rather than relying on a single simple comparison of attack rates.

The study responds to a changing global cholera landscape in which recurrent outbreaks and vaccine shortages have encouraged health authorities to use reactive campaigns, often administering a single dose of oral cholera vaccine. Most evidence for killed oral cholera vaccines has come from settings where two-dose regimens have been deployed over longer periods, leaving less information about the practical effectiveness of newer, live-attenuated alternatives when they are introduced rapidly. Vaxchora had previously shown high efficacy in human challenge studies, but its real-world performance during an active outbreak had not been established.

CVD 103-HgR is a live-attenuated vaccine, meaning it contains a weakened form of the cholera bacterium designed to stimulate immunity without causing the full clinical disease. Its one-dose schedule is operationally attractive when public-health teams need to reach a large population quickly or cannot arrange a second visit. The Mayotte analysis therefore tested a question of practical as well as biological importance: whether the vaccine’s performance would be retained when used rapidly in a community experiencing sustained transmission, rather than under the controlled exposure conditions of a challenge study.

Beyond individual protection, the researchers estimated the effect of the campaign by simulating what might have happened without vaccination. Under the baseline assumptions, the model projected that 536 cholera cases were averted, with a 95% credible interval of 240 to 824. The wider range of point estimates across sensitivity analyses extended from 152 to 1,228. This interval reflects the difficulty of inferring population-level impact from a single village outbreak, where relatively small changes in transmission, vaccine coverage, timing or case ascertainment can produce substantially different counterfactual totals.

The distinction between these two findings is central to the interpretation of the campaign. Vaccine effectiveness describes how well vaccination prevents cholera in vaccinated individuals under the conditions of the outbreak, whereas impact measures the total reduction in cases across the community, including indirect effects such as reduced transmission. High individual protection does not automatically translate into an equally precise estimate of cases prevented, especially when cases occur among people who were not vaccinated, transmission was already declining, or other control measures contributed to the observed pattern.

Taken together, the results support including live-attenuated oral cholera vaccines in reactive strategies when they are available and operationally appropriate. The findings do not mean that vaccination alone can control every outbreak: safe water, sanitation, hygiene, case detection, treatment and measures to interrupt transmission remain essential. They do, however, provide real-world evidence for a single-dose vaccine deployed during a fast-moving epidemic. The combination of high estimated effectiveness and a potentially substantial, though uncertain, reduction in cases supports Vaxchora as an additional tool in settings facing acute cholera resurgence and constrained vaccine supply, while also showing why the scale of population benefit must be assessed carefully rather than inferred from efficacy figures alone.

Subject of Research: Real-world effectiveness and population impact of single-dose Vaxchora oral cholera vaccination during the 2024 Mayotte outbreak.

Article Title: Short-term effectiveness and impact of Vaxchora vaccine during the 2024 cholera outbreak in Mayotte

Article References: Brault, A., Herry, F., Mazzilli, S., Cristancho-Fajardo, L., Froidefond, M., Epinoux, M., Berot, M., Soler, M., Lapostolle, A., Camaglia, F., Charniga, K., Cholin, T., Jean, M., Fouere, T., Ahmed, A., Niang, M., Paireau, J., Lessler, J., Azman, A. S., … Cauchemez, S. (2026). Short-term effectiveness and impact of Vaxchora vaccine during the 2024 cholera outbreak in Mayotte. Nature Communications. https://doi.org/10.1038/s41467-026-78733-0

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78733-0

Keywords: Vaxchora, cholera, Mayotte, oral cholera vaccine, CVD 103-HgR, vaccine effectiveness, outbreak modelling, disease transmission, public health, Short-term, effectiveness, impact