Imagine a disease more infectious than any other known to medical science, that would kill 2.6 million young children every year and leave millions more with deafness and even brain damage. It sounds like something from pandemic horror fiction, but such a disease does exist – measles. Yet even measles was tamed, at least for a while. In the aftermath of the successful eradication of smallpox in the 1970s, a similar global vaccination effort crushed measles mortality from 2.6 million in 1980 down to 73,000 by 2014. But vaccination rates are falling, the UK has been placed on alert and global deaths are back up to 138,000 in 2022. One response that aims to bolster herd immunity is adult MMR.