Long-lasting anti-chikungunya IgG seropositivity in the Mayotte population will not be sufficient to prevent future outbreaks: A seroprevalence study, 2019
Sustained chikungunya IgG seropositivity in the population of Mayotte will not be sufficient to prevent future epidemics: a seroprevalence study, 2019
Chikungunya is an arboviral disease transmitted by Aedes mosquitoes, causing joint pain that can progress to chronic, disabling arthritis. Although the 2023 season for specifically monitoring mosquito-borne diseases in mainland France has just begun (May 1), an article was published this month discussing the chikungunya epidemic in Mayotte and, more generally, the islands in the Indian Ocean, in 2005–2006.
In Mayotte, a French overseas department, one-third of the population was affected, i.e., approximately 40,000 cases. At that time, a serological survey aimed at determining the prevalence of anti-chikungunya antibodies showed that the recent infection rate, as assessed by the presence of IgM, was 26% in April 2006, highlighting the introduction of the chikungunya virus in Mayotte in 2005, which led to the massive epidemic on the island in 2006.
This outbreak placed immense strain on the health surveillance system, the healthcare system, and crisis management organizations. It demonstrated the urgent need to strengthen epidemiological surveillance capabilities for mosquito-borne diseases and prevention at the local and regional levels. In 2008, in Mayotte, the surveillance system for chikungunya and dengue, established in 2006, was expanded to include routine patient screening.
The seroprevalence1 study, 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.
What is the level of population protection against chikungunya infection, more than ten years after this epidemic? What are the sociodemographic factors, knowledge, and attitudes toward the prevention of mosquito-borne diseases?
3 questions for Giusepina Ortu, EPIET, Department of Infectious Diseases, Santé publique France, and Harold Noël, Department of Infectious Diseases, Santé publique France.
1- This study was conducted as part of the EPIET training program
The 2006 epidemic was a major public health event during which, according to Sissoko et al., 37% of Mayotte’s residents were infected with the chikungunya virus, which is transmitted by mosquito bites, particularly by 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. It aims to assess the risk of a new epidemic emerging after more than 10 years of low or no chikungunya virus circulation.
We were thus able to estimate the proportion of Mayotte residents carrying antibodies to the chikungunya virus using serological analyses from 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 15 years of age or older.
Vaccine trial data, chikungunya epidemiology, and data from animal studies suggest that recovery from chikungunya offers long-lasting, even lifelong protection against reinfection. Thus, this proportion of protected individuals provides the entire population of Mayotte with a level of herd immunity which, if at least equal to that observed in 2006, is likely to prevent large-scale epidemics when viruses from Africa or Asia are introduced. However, this herd immunity is affected by demographic dynamics in Mayotte, where, in particular, the 10,000 annual births have 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 years and older. However, given that 44% of Mayotte’s population is under the age of 15, only 20% of the total population would have already been exposed to the virus. An epidemic could therefore easily occur if the chikungunya virus were introduced.
By comparing our seroprevalence results with data from "Unono wa Maore," we were able to demonstrate a strong link between exposure to chikungunya and the social determinants of health and living conditions. In particular, the risk of exposure increases with lower levels of education, substandard housing, and lack of access to safe drinking water or indoor toilets. These factors reflect the fragile health situation in Mayotte, currently exacerbated by the water shortage on the island, along with social and economic difficulties.
Given this decline in herd immunity in Mayotte, it is important to move forward as quickly as possible in developing effective vaccines, a sustainable solution to prevent epidemics. The population of Mayotte will also need to play an active role in vector control by reducing mosquito larvae in and around their homes (water in containers, waste, etc.). It is important that the Regional Health Agency (ARS) and the Santé publique France Regional Unit in Mayotte maintain a high level of vigilance in the epidemiological surveillance of arboviruses in order to detect the introduction of these viruses as early as possible and to control the onset of local transmission 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 Survey
In 2018, Santé publique France conducted a general population survey ("About the Mayotte population") to assess the health needs of the population and implement appropriate prevention and health promotion campaigns. Blood samples were collected and used for a series of tests.
This survey provided an opportunity to assess the seroprevalence of various arbovirus infections, including CHIKV. Along with sample collection, sociodemographic data were gathered, along with information on attitudes and practices regarding the prevention of vector-borne diseases.
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 outbreak of chikungunya fever on Mayotte Island, France, in 2005–2006: a description based on two epidemiological surveys. Bull Epidémiol Hebd. 2007;48–49:405–7.
Renault P, Sissoko D, Ledrans M, Pierre V, Brucker G. Chikungunya outbreak on Réunion Island and Mayotte, France, 2005–2006: context and questions raised for surveillance and evaluation. Bull Epidémiol Hebd. 2008;38–39–40:343–6.
