Health authorities in the US and Europe are reporting a sudden rise in the number of people contracting measles.
Ten years ago, the infection killed 800,000 people worldwide, but aggressive vaccination campaigns have sharply reduced the global mortality rate, especially in Africa and Asia.
Yet in the US, where the disease had been declared eradicated, measles is on a comeback. Most cases are traced to unvaccinated travellers, but the highly contagious virus may also be spreading because of parents who refuse to vaccinate their children.
Al Jazeera's Tom Ackerman reports.