A measles outbreak concentrated in Amish communities across Pennsylvania and Ohio is prompting some of the affected families to reconsider their long-standing scepticism about vaccination.

The infections are clustered in areas where immunisation rates are well below the level needed to prevent transmission. Measles is among the most contagious diseases known, which means a small pocket of susceptibility is enough to sustain a chain of infection.

Community health workers say the shift in attitudes is gradual rather than dramatic, and that it has been driven less by outside messaging than by neighbours within the same families falling ill.

Public health officials warn that the lessons here extend beyond one region: the outbreak is a sharp reminder of how quickly a disease that is effectively under control can return when immunisation coverage drops.