Sustained chikungunya IgG seropositivity in the population of Mayotte will not be sufficient to prevent future epidemics: a seroprevalence study, 2019
Long-lasting anti-IgG chikungunya seropositivity in the Mayotte population will not be sufficient to prevent future outbreaks: A seroprevalence study, 2019
Chikungunya is an arboviral disease transmitted by Aedes mosquitoes, causing joint pain that can progress to chronic, disabling arthritis. As the 2023 season for targeted surveillance of mosquito-borne diseases in mainland France has just begun (May 1), an article published this month looks back at the chikungunya epidemic that struck Mayotte—and more broadly, the islands of the Indian Ocean—in 2005–2006.
In Mayotte, a French overseas department, one-third of the population was affected, representing approximately 40,000 cases. At that time, a serological survey aimed at determining the prevalence of anti-chikungunya antibodies showed that the rate of recent infection, as assessed by the presence of IgM, was 26% in April 2006, indicating that the introduction of the chikungunya virus to Mayotte in 2005 had led to the massive epidemic the island experienced in 2006.
This epidemic outbreak put the public health surveillance system, the healthcare system, and crisis management organization to the test. It highlighted the urgent need to strengthen epidemiological surveillance capabilities for mosquito-borne diseases and prevention efforts at the local and regional levels. The chikungunya and dengue surveillance system established in 2006 was expanded in 2008 in Mayotte to include systematic screening of patients.
The seroprevalence study1 recently published in the journal PLOS One [1] provides key insights for anticipating the effects of a new introduction of the chikungunya virus in this already highly vulnerable territory.
More than ten years after this epidemic, what is the level of protection among the population against chikungunya infection? What are the sociodemographic factors and the knowledge and attitudes regarding the prevention of mosquito-borne diseases?
3 questions for Giusepina Ortu, EPIET, Directorate of Infectious Diseases, Santé publique France, and Harold Noël, Directorate of Infectious Diseases, Santé publique France.
1- This study was conducted as part of an EPIET training program
The 2006 outbreak was a major public health event during which, according to Sissoko et al., 37% of Mayotte’s residents were infected with the chikungunya virus through mosquito bites, primarily from the tiger mosquito (Aedes albopictus). Our study is based on a representative sample of the Mayotte population from the Unono Wa Maore health survey conducted from December 2018 to June 2019. Its aim is to document the risk of a new outbreak occurring after more than 10 years of low or absent circulation of the chikungunya virus.
We were thus able to estimate the proportion of Mayotte residents carrying antibodies against the chikungunya virus using serological analyses conducted by the National Reference Center for Arboviruses at Marseille-IHU Méditerranée on blood samples from approximately 2,800 participants in the “Unono wa Maore” survey who were over 15 years of age.
Indeed, data from vaccine trials, the epidemiology of chikungunya, and animal experiment data suggest that recovery from chikungunya confers long-lasting, even lifelong, protection against reinfection. Furthermore, this proportion of protected individuals confers a level of herd immunity on the entire population of Mayotte which, if at least equal to that of 2006, is likely to prevent large-scale epidemics upon the introduction of viruses from Africa or Asia. However, this herd immunity is affected by Mayotte’s demographic dynamics, where, notably, the 10,000 annual births represent an equal number of people with no protection against the virus.
Our study suggests that, with a chikungunya seroprevalence of 34.75%, the level of protection against the chikungunya virus would remain relatively high in 2019 among Mayotte residents aged 15 and older. However, given that 44% of Mayotte’s population is under the age of 15, only 20% of the total population would have been exposed to the virus. An epidemic could therefore easily break out if the chikungunya virus were introduced.
By cross-referencing our seroprevalence results with data from “Unono wa Maore,” we were able to highlight a strong link between exposure to chikungunya and social determinants of health and living conditions. In particular, the risk of exposure increases with lower levels of education, precarious housing, and a lack of access to drinking water or toilets in the home. These factors reflect the delicate health situation in Mayotte, currently exacerbated by the island’s water shortage and social and economic difficulties.
Given this decline in herd immunity in Mayotte, it is crucial to buy as much time as possible for the development of effective vaccines, which offer a sustainable solution for preventing epidemics. It will also be necessary to engage the population of Mayotte in vector control efforts by reducing mosquito breeding sites in and around their homes (standing water in small containers, trash, etc.). It is important that the ARS and the Regional Public Health France Unit in Mayotte maintain a high level of vigilance in epidemiological surveillance of arboviruses in order to detect any introduction of these viruses as early as possible and to control any initial local transmission of the virus through mosquito control measures.
[1] Ortu G, Grard G, Parenton F, Ruello M, Paty M-C, Durand GA, et al. (2023) Long-lasting anti-IgG chikungunya seropositivity in the Mayotte population will not be sufficient to prevent future outbreaks: A seroprevalence study, 2019.
The Unono wa Maore Investigation
SurveyIn 2018, Santé publique France launched a general population survey (“À propos du Mahorais”) to assess the population’s health needs and implement appropriate prevention and health promotion campaigns. Blood samples were collected and made available for a series of analyses.
This survey provided an opportunity to assess the seroprevalence of various arbovirus infections, including CHIKV. Alongside the collection of these samples, sociodemographic data were collected, along with information on attitudes and practices regarding the prevention of vector-borne diseases.
Learn more about surveillance systems:
In Mayotte:
Dengue-like syndromes in Mayotte. Update as of July 10, 2021. Santé publique France
Sissoko D, Moendandze A, Malvy D, Giry C, Ezzedine K, Solet JL, Pierre V. Seroprevalence and risk factors of chikungunya virus infection in Mayotte, Indian Ocean, 2005–2006: a population-based survey. PLoS One. 2008 Aug 26;3(8):e3066. doi: 10.1371/journal.pone.0003066. PMID: 18725980; PMCID: PMC2518850.
In mainland France
On the 2025–2026 epidemic:
Sissoko D, Delmas G, Giry C, Petinelli F, Saidali R, Gabrie P, Abaine A, Paquet C, Pierre V. Massive chikungunya fever outbreak in Mayotte, France, in 2005–2006: description based on the results of two epidemiological surveys. Bull Epidémiol Hebd. 2007;48-49:405-7.
Renault P, Sissoko D, Ledrans M, Pierre V, Brucker G. The chikungunya epidemic in Réunion and Mayotte, France, 2005–2006: the context and issues of surveillance and evaluation raised. Bull Epidémiol Hebd. 2008;38–39–40:343–6.
