The 18 recorded cases “are mostly young adults working at the station this season,” the ARS regional health agency for the Auvergne-Rhone-Alpes district said.
It recommended that parents ensure that they and their children are vaccinated against the highly contagious disease, as thousands of families prepare to hit the slopes during winter school vacations in the coming weeks.
Beyond the outbreak at Val-Tho, as it is popularly known by skiers, the agency said 12 other cases had been registered in the region since February 4.
Cases have been rising in France and other parts of the developed world in recent years, the result of fewer children being vaccinated against a viral disease that causes rashes and inflammation which can quickly prove fatal.
The ARS recorded just eight cases in the Auvergne-Rhone-Alpes region in 2016, a figure that jumped to 45 in 2017 and hit 84 last year.