Measles in vulnerable populations: An outbreak in Roma settlements of Loire-Atlantique, France, 2019.

In May 2019, a measles outbreak occurred in the French subregion of Loire-Atlantique, particularly affecting Roma settlements. Various obstacles hindered the implementation of postexposure measures among Roma population, resulting in the spread of the cases to other settlements. Suspected cases of measles were immediately investigated and concerned settlements were visited for measles-mumps-rubella (MMR) vaccination. From July 1 to September 3, 2019, a first and then a second Health Reserve team helped for vaccination on the affected and then also the measles-free settlements. Vaccination uptake was monitored with the use of the department's vaccination center immunization registry. Genotyping of selected samples was performed for comparison with viruses circulating at the same time in France and Romania. As of September 16 2019, 109 cases of measles were confirmed among Roma population, including 99 (91%) children under 15 years. Of the 85 people eligible for vaccination, 60 (71%) had not been vaccinated and 23 (27%) had an unknown vaccination status. Sequence comparison revealed that 28/29 sequenced D8 strains were 100% identical to the strain responsible for a large number of cases throughout France in 2019, and to two sequences reported in Romania among sporadic cases. The vaccination campaign resulted in 1136 people on 35 settlements receiving at least one dose of MMR vaccine and in the increase of one-dose MMR vaccine coverage at 24 months from 43% (23/53) to 91% (48/53). With measles transmission continuing in Europe, efforts must be made to meet immunization coverage targets, particularly in hard-to-reach communities where outbreaks may be difficult to control.