Measles virus circulation between the State members of the Indian Ocean Commission?

Abstract

Background: Despite the availability of safe and effective vaccines, measles resurgence has been observed worldwide in 2018 and 2019. In West Indian Ocean (WIO), almost all islands have reported measles cases during these years. Vaccine coverage was particularly low in Madagascar and Comoros Island, with a single dose provided by the Expanded Program on Immunization. Because of intense exchanges between WIO islands, outbreaks observed in WIO were probably related. Methods and materials: Thanks to the Epidemic Intelligence Unit and the SEGA-One Health network of the Indian Ocean Commission (IOC), composed of five countries (Comoros, Madagascar, Mauritius, France (Reunion), and Seychelles), epidemiological data from each surveillance system were shared. Results: Measles outbreaks have successively occurred in: Mauritius (W12/2018), Madagascar (W35/2018), Reunion (W51/2018) and Comoros (W21/2019; first cases were reported early 2019). As of W41/2019, Madagascar was the most affected island with 244 557 cases (attack rate around 929/100 000) and a case fatality rate of 0,4%. Attack rate was lower in Mauritius (117/100 000) were 1 482 and 4 deaths were reported. In Reunion and Comoros, respectively 96 and 132 cases (of whom 62 were confirmed) were reported; no deaths were reported. Two measles genotypes were circulating in the region: genotype B3 in Madagascar and Comoros; genotype D8 in Mauritius; in Reunion Island both genotypes were observed. Only one case was reported in December 2018 in Seychelles were 2-dose vaccine coverage reached 99% in 2017. Conclusion: Given starting date of each outbreak and circulating genotypes, it can be assumed that outbreaks were closely related, measles virus circulating especially between Mauritius and Reunion on the one hand, and between Madagascar, Comoros and Reunion on the other hand. WIO islands are considered as an epidemiological block where pathogens easily circulate through human and animal exchanges. This situation underlines the importance of the SEGA network which should be further strengthened. For example, development of biological cooperation between WIO islands could help comprehensive epidemiological analyses in the course of outbreaks.