The latest World Health Organization report on measles epidemics shows that cases jumped by 50% last year. In one of the poorest and least connected countries in the world, Madagascar, nearly a thousand children are reported to have died after a measles outbreak in the countryside. The real figure is likely to be much higher, because of difficulties of reporting. An emergency programme of vaccination seems to have contained that epidemic for the moment but it is a reminder of how devastating the disease can be against unprepared populations. In the rich world, meanwhile, previously prepared populations are having their defences dismantled from the inside.

The discovery of ad campaigns against vaccination on Facebook that are carefully targeted at pregnant women is unusually worrying. It shows how the widespread availability of sophisticated advertising techniques is going to give considerable power to people who previously had no way of getting their message across to large numbers. In the most recent US campaigns against vaccination, 147 different advertisements have been used and some viewed more than 5m times. There is an arms race under way, whether we like it or not.