A GP in Hackney sends out the same letter she sent five years ago, only this time the tone is different. Then it was a reminder. Now it reads like a warning. Measles has been circulating in England for eighteen months without a break, the World Health Organization stripped Britain of its elimination status in January, and this week NHS England began writing to roughly a million families whose children have missed one or both doses of the vaccine that is supposed to stop it. The letters will arrive through the NHS App, by text, by post, through GPs who know their patches well enough to guess which doorsteps need a knock rather than a message. It is a large, well-organised operation. It also concedes something the health service does not often say out loud: that routine immunisation, the most basic and cost-effective intervention in public health, has been allowed to slip.

The numbers explain the urgency. More than eight hundred confirmed measles cases and two deaths in the first half of this year already approach the total for the whole of 2025. MMR coverage in five-year-olds sits at 84.1 per cent, eleven points short of the threshold the WHO says is needed to stop the disease circulating, and the gap between the most and least deprived areas of the country runs to seven and a half percentage points. That gap is the real story. Measles does not spread evenly. It finds the postcodes where health visiting has been thinned out, where GP list sizes have grown, where trust in institutions was already fraying before a pandemic accelerated the decline. The new four-in-one jab, folding chickenpox protection into the MMR schedule, is a sensible simplification. It does not by itself fix the access problem that sits underneath the coverage figures.

This is where the story stops being a public health footnote and becomes a governance one. Academics at the London School of Hygiene and Tropical Medicine have pointed out, reasonably, that the burden of childhood immunisation rests on primary care, and that the integrated care boards responsible for commissioning and funding that work are being asked to cut running costs by as much as half. Restructuring on that scale rarely spares outreach and community engagement, the unglamorous work that persuades a hesitant parent to bring a child back for a second dose. Sir Jim Mackey's accountability agenda has focused NHS attention on elective waiting times and financial grip, for good reason, but a target regime built around measurable throughput has a way of squeezing out the preventive work that shows up in outcomes years later rather than next quarter.

There is also a simple continuity problem. James Murray is the ninth health secretary in a decade, appointed after Wes Streeting's resignation amid the wider convulsions at the top of government this year. Every change of secretary of state brings a change of emphasis, and public health campaigns depend on precisely the opposite: years of unglamorous consistency, stable funding lines and ministers willing to keep talking about vaccination when there is no crisis to justify a press conference. Losing elimination status was not caused by any single decision. It was the accumulation of small retreats across a decade, each individually defensible, none of them reversed in time.

The catch-up campaign will likely work, in the narrow sense that letters will bring some families back through the door. But a health system that has to write to a million households to recover ground it once held automatically is admitting that prevention has become optional in practice, however central it remains in policy documents. Andy Burnham's allies talk about a fresh start for Labour's health agenda. If there is one lesson from this episode worth carrying into that reset, it is that resilience in public health is built in the years nobody is watching, not in the catch-up letters sent out once the damage has already been counted.