On 28 February 1998 the Lancet published a study with the inauspicious title “Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children.”1 The paper has been much criticised, and the Lancet finally retracted it this week. But why did it all take so long?

The story is well known. Wakefield’s paper implied an association, later shown to be spurious, between gastrointestinal illness, the combined measles, mumps, and rubella (MMR) vaccine, and an autism-like disorder in a sample of 12 children. At a controversial press conference Wakefield appeared to conflate association with causation, and in the eyes of the tabloid press his tiny, skewed sample represented children in general. The immunisation record of then prime minister Tony Blair’s infant son became the most politically sensitive item of data held in the NHS. Private clinics enjoyed a brief boost to business by offering the three vaccines as separate, spaced injections as recommended by Wakefield. Measles returned—and did considerable damage.

On 18 February …