Why you should download the COVID19 app

The contribution to the R0 value from presymptomatic transmission is roughly 0.9, almost enough to generate renewed exponential growth on it's own. See quote from Ferretti et al below.

As restrictions are lifted (and people inevitably relax their social distancing mentality) then we need a new weapon to enable rapid tracing and isolation of people who have been in contact with an infected person. Manual contact tracing is too slow.

More details:
covid-19 Roadmap to Recovery (critical analysis of the government roadmap)

Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing by Ferretti et al

Specifically, our approaches suggest that between a third and a half of transmissions occur from pre-symptomatic individuals. This is in line with estimates of 48% of transmission being pre- symptomatic in Singapore and 62% in Tianjin, China (30), and 44% in transmission pairs from various countries (31). Our infectiousness model suggests that the total contribution to R 0 from pre-symptomatics is 0.9 (0.2 - 1.1), almost enough to sustain an epidemic on its own. For SARS, the corresponding estimate was almost zero (9), immediately telling us that different containment strategies will be needed for COVID-19.

Transmission occurring rapidly and before symptoms, as we have found, implies that the epidemic is highly unlikely to be contained by solely isolating symptomatic individuals. Published models (9–11, 32) suggest that in practice manual contact tracing can only improve on this to a limited extent: it is too slow, and cannot be scaled up once the epidemic grows beyond the early phase, due to limited personnel. Using mobile phones to measure infectious disease contact networks has been proposed previously (33–35). Considering our quantification of SARS-CoV-2 transmission, we suggest that this approach, with a mobile phone App implementing instantaneous contact tracing, could reduce transmission enough to achieve R < 1 and sustained epidemic suppression, stopping the virus from spreading further. We have developed a web interface to explore the uncertainty in our modelling assumptions (here). This will also serve as an ongoing resource as new data becomes available and as the epidemic evolves.

Update 1 (May 6):
Having persuaded myself to download the app I receive a message on PlayStore "Your device isn't compatible with this version". Googling to understand I found on a Whirlpool thread that you need "Android 6 or above". I have Android 5.1.1. mmm ... time for a new phone or should I just curse the darkness / government?

Update 2 (May 27):
How did the Covidsafe app go from being vital to almost irrelevant?

Where the app has faltered has been in transparency. Developers have reported difficulty communicating with the Digital Transformation Agency about problems.

Early on developers noted the iPhone version would not be able to exchange Bluetooth handshakes with other devices unless it was running on the screen – incredibly impractical for users.

The government initially denied this, refused to answer questions about it, and only once, before the Covid-19 senate committee, did the agencys chief executive, Randall Brugeaud, admit the Bluetooth function suffered when the app wasn’t on screen.

Update 3 (May 27):
A flood of coronavirus apps are tracking us. Now it’s time to keep track of them
This article evaluates various COVID tracer apps being used around the world in line with these principles:

• Is it voluntary? In some cases, apps are opt-in—but in other places many or all citizens are compelled to download and use them.
• Are there limitations on how the data gets used? Data may sometimes be used for purposes other than public health, such as law enforcement—and that may last longer than covid-19.
• Will data be destroyed after a period of time? The data the apps collect should not last forever. If it is automatically deleted in a reasonable amount of time (usually a maximum of around 30 days) or the app allows users to manually delete their own data, we award a star.
• Is data collection minimized? Does the app collect only the information it needs to do what it says?
• Is the effort transparent? Transparency can take the form of clear, publicly available policies and design, an open-source code base, or all of these.

The Australian app gets 4 stars out of 5, failing on the transparency issue.