Polio has been largely eliminated around the world, but it has made comebacks. In Israel, an outbreak in 2013 prompted authorities to launch a campaign to give people the live, oral vaccine. Poliovirus particles are shed in the faeces, and can spread even when infected people do not show symptoms, leading to ‘silent’ outbreaks.
Yakir Berchenko at Ben-Gurion University of the Negev in Beer-Sheva, Israel, and his colleagues analysed data collected during the 2013 outbreak on levels of virus particles derived from the live vaccine that were found in sewage from seven Israeli towns. They also looked at the number of people from those areas who received the vaccine. Using that data, the team came up with a statistical tool that predicted the number of people who were shedding the virus, based on its levels in sewage samples.
The method could be used to estimate the size of future polio outbreaks and to determine whether a vaccination programme has fully ended an outbreak.