The Covid-19 App -Why do we need it?

bluetooth centralised contacttracking covid-19 decentralised devices epidemiologicalmodels exposurenotifications geolocation NHSXapp notifications privacy safety track&trace trackingapps virus

We all have fears about our privacy safety with these new Google/Apple supported Covid-19 Apps, so many questions about how will it work and what information will it store about me?

Let us start with why we need a tracking device at all. 

Throughout our history we have had huge waves of infections, from the Black Plague sweeping across Europe in the middle ages, to the outbreak in London in 1854 of Cholera, to name just a couple of examples. Each outbreak had started from somewhere and then spread, but the answer, in all cases, to try and stop the spread was to find the source and track from there, it’s path (Track & Trace)

An historical source wrote about the Black Death: ‘In Melcombe, in the county of Dorset, two ships came alongside. One of the sailors had brought with him from Gascony the seeds of the terrible pestilence and, through him, the men of that town were the first in England to be infected.’

In 1854, a leading scientific figure, Dr John Snow researched the outbreak of Cholera in London, speaking to people in the infected areas and trying to understand where it had begun and how it was spreading. (Germ Theory had not been discovered yet!) Eventually Dr Snow worked out that the source was a contaminated water pump in Broad Street. Shutting the pump down stopped the spread of the terrible disease. (Again, using track & trace)

A researcher called George Soper investigated the isolated outbreaks of Typhoid between 1900-1907, which was generally thought to be caught in unclean environments, but when rich households became infected, George discovered that the source was a cook called Mary Mallon, who was a carrier but showed no symptoms and she was infecting the households that she worked in. She is known in history as Typhoid Mary.

All these stories involved track and tracing to try and contain the contagion.

Obviously, our understanding of diseases and transmissions are a lot more advanced now, and our methods for being able to track and trace are a lot more sophisticated and instant.

Hence, we are now being introduced to the new Apps to track and trace Covid-19. Many countries around the globe run these with great success. Here in Britain, the NHSX are formatting an app, but the news is, that it probably will not be available until Winter 2021. This is just one part of the strategy to track and trace, the government have joined with the global epidemiological models, which have been developed by experts to ensure that the information gained from these models meets the medical needs but also ensures that the technical safety and privacy issues are met. Apple & Google are involved with support on all these Models. An example of their support service is already visible on all our google accounts where you will see a ‘Covid-19 exposure Notifications’ service.( Don’t worry, it won’t be working on your device yet, you have to install a participating App and turn on Bluetooth and Geo-Location for this to start up.)

All contact tracing apps have one thing in common; they record when you’re close to someone else (usually in a way that preserves your privacy) and try to characterise how close, and for how long

Centralised and Decentralised models? What does that mean?

Decentralised Model- you tell the system you are ill and give it no extra information. Periodically, it collects a list of everyone who has said they’re ill, and sends it out to all users of the app. Individual devices look to see if any of its local contacts are on the list, and tells their user if this is the case. Notifications will lead to some health interventions, probably self-isolation to start with. In this decentralised model:

  • every user of the app gets some understanding of who is declared ill (and that list keeps being updated)
  • the public health authority - by design - knows pretty much nothing about ill people

Centralised Model- an ill user reports their symptoms, but also gives all their anonymous contacts to the public health authority, along with some details about the type of contact they have had (duration and proximity for example). The health authority can use risk modelling to decide which contacts are most at risk, and then notify them to take some action - again probably self-isolation to start with. Importantly, the public health authority has anonymous data to help it understand how the disease appears to be spreading and has the anonymous contact graphs to carry out some analysis. So, the health authority could discover that a particular anonymous person seems to infect people really well. While the system would not know who they are, encounters with them could be scored as riskier, and adjust the risk of someone being infected by a particular encounter appropriately. The NHS app uses this centralised model, but also protects your security and privacy strongly.

At the end of the day (at the moment!) it is our own personal decision whether to download a track and trace App, it’s a question of personal privacy over National (and global) safety, which is the less of the two evils!? A hard but necessary choice if we want to try and get our country and world back to some sort of normality.




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