Key Points

• Among suspected measles cases occurring between January 1 and December 31, 2023, 117 cases of measles, including 31 imported cases, were reported throughout France (compared to 15, 16, and 240 cases in 2022, 2021, and 2020, respectively). While the number of cases has increased eightfold compared to 2022, it remains very low compared to the pre-COVID-19 period.

• In total, 16 departments reported at least one case. No cases were reported in the overseas territories.

• The age distribution of cases shifted in 2023 toward older age groups compared to previous years, with a median age of 12, linked to an outbreak among middle school students.

• The incidence rate of reported cases was 0.13 cases per 100,000 inhabitants (excluding imported cases). The highest incidence rate was observed, unusually, among young adolescents (10–14 years old): 1.17 cases per 100,000 inhabitants with 50 reported cases, representing 58% of reported cases (excluding imported cases and cases residing abroad). The incidence rate among infants under one year of age remained stable compared to previous years at 0.41 cases per 100,000 inhabitants, with a limited number of cases (only 5 cases).

• Twenty-seven cases were hospitalized, including two in intensive care. Hospitalizations primarily involved children under 5 years of age and adults over 30 years of age. Twelve cases developed complications, including 9 cases of pneumonia. Half of the reported complications involved adults over 30 years of age. No deaths were reported.

• Among the 96 cases eligible for vaccination (aged ≥ 1 year and born since 1980) with known vaccination status, 44% were not vaccinated against measles according to the recommended schedule, 9% had received one dose, 46% had received two doses, and 1% had been vaccinated without the number of doses received being specified. No complications and only one hospitalization were reported among properly vaccinated individuals. The majority of cases vaccinated with two doses involved middle school students, most of whom had received an early (before 12 months) administration of the first vaccine dose; this could explain the lower long-term protection observed in these adolescents.

• A notable increase (sixfold) in imported cases was observed (31 cases in 2023 versus 5 in 2022), more than half of whom were unvaccinated. These cases originated from fifteen different countries and spanned all continents except the Americas. The genotypes identified were B3 and D8. These cases generated chains of transmission within France, leading to the emergence of four outbreaks of varying sizes (ranging from 2 to 64 cases in total), bringing the proportion of reported cases linked to a possible importation from abroad to 84% and reflecting the resurgence of measles circulation internationally.

• Seven outbreaks (including the four mentioned above) were observed in 2023. They occurred in schools, family circles, and hospital settings, resulting in nosocomial cases. The largest cluster of cases was reported in Auvergne-Rhône-Alpes, with 64 cases of measles reported between August and November 2023, primarily involving middle school students who were properly vaccinated.