
Ask HN: Plausibility of an idea to limit the spread of Covid-19 - chimprich
The challenge of the current COVID-19 pandemic is well-known.<p>Could a voluntary user-tracking app help reduce the R0 level of the COVID-19 virus?<p>One of the main challenges with this virus is that carriers of the virus become infectious well before they show symptoms. Consequently, they pass on the infection before they can be isolated.<p>Apps such as Google Maps already track users&#x27; movements to a high level of precision. A similar app could be created that tracked users&#x27; movements and notified people they had interacted with if they got infected.<p>It would work like this:<p><pre><code>  - Users&#x27; movements are tracked

  - Upon developing a fever (etc.) the user notifies the app

  - The app checks their movements during the estimated period they could have been infectious

  - Every other user who was in their presence for X minutes gets notified and requested to isolate themselves

  - Recursively check those users&#x27; movements to see if they may have passed on the virus
</code></pre>
Disadvantages I can think of off the top of my head:<p><pre><code>  - Requires simultaneous voluntary use by a large proportion of a regional population

  - Possibility of false positives by bad actors (would an occasional false positive be so bad)?

  - Requires some minimal altruism by the user (they won&#x27;t be helped directly)</code></pre>
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DanBC
Bob flies from Ireland to Cheltenham in the UK to visit the Cheltenham Gold
Cup. While there he mixes with about 60,000 other visitors to the races, along
with the 100,000 or so residents of Cheltenham.

Who gets traced?

[https://twitter.com/carolvorders/status/1237653282761383937?...](https://twitter.com/carolvorders/status/1237653282761383937?s=20)

~~~
chimprich
I think those gatherings are a thing of the past in most countries.

But in practice I don't think you'd have that many notifications (there's not
that many people you'd stand next to for, say, 5 minutes within 1 metre) and
they could all be true positives.

------
eesmith
I know of a couple who bought a clock radio connected to the emergency weather
system. When a notice went out, the radio would turn on so you could hear it.
They thought it would be useful, as they lived in in a tornado area, and would
like a warning if they were asleep.

Problem is, it wasn't that localized. It would wake them for alerts that were
100 miles away, and which didn't affect them.

They stopped using the alarm.

In general, people won't use a service like what you describe unless it's
really actionable. And I don't think this system has a high false positive
rate (and high false negative rate) so there isn't good actionable information
beyond what general precautions (social distancing, good hand hygiene, etc.)
offer.

\- What percentage of people get fevers from other reasons? That is, even
without bad actors, people are going to report fevers, and those might
overwhelm the actual positives.

\- How close does your infection model (X minutes within distance Y) match the
actual infection mechanism and rate? I suspect it isn't that good, and will
include many people who aren't infected.

~~~
chimprich
Thanks for the thoughts on this.

> What percentage of people get fevers from other reasons?

Interesting. Other infectious diseases (flu/colds) seem to be going down in
countries with lockdowns so this may not be such a big issue.

> \- How close does your infection model (X minutes within distance Y) match
> the actual infection mechanism and rate? I suspect it isn't that good, and
> will include many people who aren't infected.

I pitched this idea to a leading epidemiologist and he thought the mechanism
would work.

~~~
eesmith
[https://www.cdc.gov/flu/weekly/index.htm](https://www.cdc.gov/flu/weekly/index.htm)
says (of the current US flu season): "CDC estimates that so far this season
there have been at least 36 million flu illnesses, 370,000 hospitalizations
and 22,000 deaths from flu."

If 50% of the 36 million flu illnesses had a fever, and the flu season is 23
weeks long (the records start in 201940), and the flu lasts for one week, then
that's over 750,000 people each week with a fever, on average.

That number far outweighs the current numbers for people with COVID-19
symptoms, so gives a large false-negative signal _in the current situation_.

As the number of cases increase, the signal-to-noise ratio changes. But at
some point, specialized per-person notification is no better than general
advice to the entire population.

You mention that the numbers for flu/colds "seem to be going down in countries
with lockdowns."

FWIW, it's also going down in the US without lockdowns. That's because we are
approaching the end of the flu season. See the CDC chart just under the text
"In the most recent three weeks, influenza A viruses are the most commonly
reported influenza viruses in all age groups." in my earlier link.

~~~
chimprich
Thanks, interesting. It might be the case that the app would only be useful
once the levels of infection increase, or perhaps the app would only instruct
the user to send an alert when they had developed a fever + dry cough, which
seems more typical of this virus.

> But at some point, specialized per-person notification is no better than
> general advice to the entire population.

I take your point, but I think targetted "you have had a good chance of being
exposed" is far more likely to result in action than "minimise contact with
other people if possible".

A preprint of a paper which looks like has similar ideas but some more formal
modelling:
[https://www.medrxiv.org/content/10.1101/2020.03.08.20032946v...](https://www.medrxiv.org/content/10.1101/2020.03.08.20032946v1)

~~~
eesmith
I looked at that paper but it gave no indication of how the app was supposed
to implement algorithmic contact tracing. I think it assume that that method
would always be better than the current system? If so, there's no presented
evidence that that's true.

I also can't figure out why you and are are downvoted for our low-key
discussion in a days-old posting, so I've up-voted you.

------
drKarl
I think they have an app like that in China, although I think people in
western countries would probably not be that willing to use it, for privacy
concerns, and it would probably also violate GDPR.

~~~
chimprich
Surely privacy concerns are secondary under the current outbreak? And would
GDPR be so important if a user opted out?

