Overt resistance is much less common. There are a small number of “new age” parents, whose preferences for alternative medicine could probably be accommodated without compromising herd immunity.

Of more concern is the emerging group of affluent parents who are opting out because they believe they can micromanage all risks to their children. This group has not been studied in the UK, but recent work in California found that where there is a critical mass of parents who think this way in a school catchment, refusal rates are high because the parents believe that the minimal risks from vaccination need not be accepted. They can insulate their children from the “others” who carry infectious disease. Their children do not share school classrooms, public transport or public leisure facilities with children from poorer backgrounds. Their children’s social contacts are carefully supervised so that they only mix with other children from a similar background whose parents think in the same way. They seem to be the forerunners of the “helicopter parents” who hover over their children at university and even into first employment.

We may need to relearn the lessons that drove public health reform in 19th-century Britain: infectious diseases are a potential threat to everyone. No one can buy protection on an individual basis.

Why are vaccination rates in England falling?