The finding of a polio virus in repeated sampling from the sewage system in London during 2022 is less of a concern for highly vaccinated communities in the UK, where children are immune to the rare chance of paralysis. However, it is a portent of potential individual catastrophe for families with unvaccinated and undervaccinated children in our capital unless there is urgent action. In these pandemic times, we shouldn’t need much reminding that there are some bad viruses out there, and there always have been. But intervening urgently to control epidemics and outbreaks with vaccines is relatively new. The devastating polio epidemics of the 1940s and 1950s, which left thousands of children paralysed in the UK, were very much in the public eye at the time, with the familiar images of hospitals full of children in coffin-like iron lungs or paralysed children with their legs in callipers. These epidemics were finally extinguished in many countries as a result of the mass deployment of two different polio vaccines by Jonas Salk and Albert Sabin. Here, the success of the polio programme led to the formation of JCVI, the Joint Committee on Vaccination and Immunisation in 1963, and development of a coordinated immunisation programme that protects our children to this day. By the 1980s, despite the invention of the vaccine 30 years earlier, there were still more than 300,000 yearly polio cases worldwide because of failures in coordination globally and lack of deployment in many countries. But, as a result of huge efforts, a remarkable impact has been seen since then. Two of the three types of wild polio virus (type 2 and type 3) have been driven to extinction by vaccine immunity; only type 1 is left. It may be possible to eradicate this virus completely from the world. And we are very close to seeing the back of it – in the past 12 months there were only 16 documented cases of paralytic polio caused by the remaining type 1 virus globally (down from 176 cases in 2019). This success has largely been driven by use of Sabin’s live oral vaccine, which anyone over the age of 18 will have received as drops by mouth or, like me, will fondly remember as a dose on a sugar cube. This vaccine is especially good at preventing the disease and also halting transmission of the virus. It has already stopped polio in most of the world. There are huge efforts towards eradication, focused on improving vaccine coverage in the few remaining countries where the virus is still found, with most attention on improving access in Afghanistan and Pakistan. It is 42 years since smallpox was eradicated, could it be time for polio? We are not there yet and there were some notable setbacks with cases in Malawi and Mozambique in the last year, but the end of another menace of history feels possible. While we are tantalisingly close to eradicating wild polio, it isn’t straightforward. The live Sabin vaccine, which has been saving the world from polio epidemics for 70 years, can very rarely undergo freak mutations, which paradoxically renders it capable of causing paralysis in undervaccinated populations. Nevertheless, the Sabin vaccine continues to be a critical part of the global programme because of its special characteristics in improving immune responses in the gut and thereby reducing spread of wild polio. Now that polio is on the retreat, greater attention is being turned towards avoiding rare cases of paralysis caused by mutated Sabin viruses. The most important part of the approach is, perhaps counterintuitively, to improve vaccine coverage with the Sabin vaccine, as paralysis does not happen in highly immune populations. Many countries that have managed to eliminate the virus, usually using the live Sabin vaccine, have changed to using the Salk vaccine. The Salk vaccine contains a killed virus that cannot mutate or spread and has been part of the routine vaccine programme in the UK since 2004. All children in the UK are offered five doses of the injected Salk polio vaccine during childhood. It is an imported Sabin virus in the sewage in London that threatens children there, and the risk can be eliminated by improving vaccine coverage. Unfortunately, some of the lowest vaccine coverage in the UK is in some parts of London, in the very places where children are at potential risk from this virus. The solution is simple, free and safe: children who haven’t had a dose, or have missed doses, must get vaccinated as soon as possible. Polio isn’t the only vaccine-preventable disease out there, and can strike if we drop our guard and let vaccine coverage fall. Outbreaks of measles, mumps and diphtheria have all occurred in undervaccinated individuals in the UK over the past decade. Vaccines are immensely powerful in controlling infectious threats – but they only work if we use them. Prof Sir Andrew Pollard is Director of the Oxford Vaccine Group, University of Oxford