> For the complete documentation index, see [llms.txt](https://prep.pathcheck.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prep.pathcheck.org/background.md).
# Background
For hurricanes, we use satellites to sense the progress of the hurricane and then give instructions to help citizens avoid the storm. 10 years ago, during the 2009 flu pandemic, the best we could do was to sense the extent of contagion and overall prevalence using surveillance technologies and then create and enforce regulations to address these challenges.
Today smartphones are our new sensors. We can gather data from smartphone applications to create personalized alerts for everyone in the system.
Imagine John, a refugee in Sao Paulo, Brazil. He's at a social event and is exposed to a virus. After some time he has an onset of symptoms and gets tested. Later he is treated and eventually vaccinated. At present, most of the information about John’s user journey is hidden or disjointed from public health.
As public health uses test-trace-and-vaccinate programs to predict virus spread and alert citizens, significant gaps emerge in the data. Some countries resorted to draconian measures to harness citizen data for filling the gaps. With a surveillance state, they managed to tame the pandemic within three months.\
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