Tuesday, 7 April 2020

Corona Virus Update: tracking infections by App and do go outside (part 27)


Prof. Dr. Christian Drosten
This edition of the Corona Virus Update Podcast was about how effective an App could be that monitors with whom we have been in close contact lately and warns them if we develop symptoms or are tested positively.

Even if it is voluntary and only a part of the population uses the App, in addition to only a part heading its warning to stay inside it would have a drastic effect, which is comparable to a lockdown.

In addition informatics researchers think this tracking can be done in a way that respects the users privacy. Only who was close for a longer time is stored (this is determined by the short-range Bluetooth transmitter of your mobile phone). No locations are stored; if all data were on a national server, the contact information would allow very accurate estimates of ones position, but the contacts are stored on your own phone. Only when someone reports to be ill, this information would go to a national server and all other users could anonymously check this encrypted information. This seems to be a powerful way to fight the virus and would enable other restrictions to be release. If they can deliver on privacy claims, the software is open source, so we can check and the use of the App is voluntary, I would be in.

[EDIT: It possible to deliver the privacy promises, the CCC writes: "With the help of these technologies, it is possible to unfold the epidemilogical potential of contact tracing without creating a privacy disaster." The CCC are Germany's prime technology experts and privacy activists. I will follow their advice.

This contact tracing App should not be confused with the Corona Data Donation App ("Corona-Datenspende-App") of the Robert Koch-Institut, which was launched today for Android and iOS. This voluntary App uploads data from your fitness-tracker to estimate statistically how many people are ill from their temperature or pulse. This is a lot of private information, but these people already uploaded all this information to a corporation. It is only pseudonymous and only needs to be used by a much smaller part of the population to be useful for monitoring the situation and scientific research. As long as participants give informed consent and data can be deleted again this is fine.]

To make the computations on how effective the App would be, one needs estimates for how the virus in transmitted. This study computed that without intervention one person infects two others. (Other studies seem to be in the range of two to three.) About half of these infections are after symptoms appear and about half before. Because of this it is not enough to only isolate people with symptoms.

The other two factions are much smaller: On average one infected person infects 0.2 via contact infections (environmental transmission) and people who do not show any symptoms are responsible for 0.1 infections (asymptomatic transmission).

A part of the interview I skipped was about Trump's favorite drug, hydroxychloroquine and in particular about a new medRxiv, preprint on this drug. There is no clear evidence at the moment, so this only interesting in the light of Trump pushing it so hard, but less from a science point of view.

At the end is a question on what people can do themselves to strengthen their immune system: go out and do sports. Going out while keeping your distance is not an infection danger.

Prof. Dr. Christian Drosten specialises in emerging viruses and developed the WHO test; more on his background. This episode science journalist Anja Martini asks the questions.

The epidemiological model behind the App


Anja Martini:
93 percent of Germans are in favour of the restrictions, i.e. the social distancing rules and staying at home. This is the result of a [high quality] survey. When it comes to setting up a mobile phone App, Germans are divided.

Mr. Drosten, I remember at the beginning of the podcast [series] we talked briefly about apps in China and South Korea that analyse the movement data of mobile phone users in order to find possible infected persons. At that time you said that this was probably difficult in Germany, and I agreed with you.

The situation has now changed. In other words, we are now talking about apps that work anonymously via Bluetooth and that work on a voluntary basis. There is already a first study from Oxford, involving scientists across Europe. What do you make of it?
Christian Drosten:
Yes, this is a study from the group of Christophe Fraser, certainly one of the best epidemiological modelers. It's a very interesting study, I think. It's published in Science. It is about first of all calculating a much better, more accurate epidemiological model, which is simply much more fine-grained, where more information goes into it than was known until recently. The fact is that the scientific literature provides more and more data that can be evaluated and then fed into such models.

The beginning of this study is actually made from the observation that there are now actually more and more descriptions of transmission pairs in the literature and therefore the [[serial interval]] of this infection can actually be better determined. So how long does it take from symptom to symptom or from infection to infection. With symptom to symptom one speaks of "clinical onset serial interval", with the other - from infection to infection - of serial interval. And what you actually need is the serial interval itself. But it's all relatively difficult to quantify exactly determine. That is why one can at least make a good approximation over the "clinical onset serial interval".

This can then be derived again, also from literature reports, and that is how the study starts. 40 pairs of transmission from the literature are evaluated, they feed an already existing mathematical model to derive certain parameters and certain proportions of the overall transmission activity.

The [[basic reproduction number R0]], has been recalculated here as two. That is a relatively low value, if you look at what other analyses have found before. In some cases it was more like two and a half.

Anja Martini:
So [the study computes that] one person infects two others.

Christian Drosten:
Right. Now we have the option of decomposing these transfers into parts. ... The asymptomatic [part] means a carrier that never shows symptoms. And pre-symptomatic [part] of course means that it is transmitted before the carrier has symptoms. But you can find this carrier later, because he gets symptoms then. So of course you can still identify the contact patients later. This is a consideration that will be discussed later in the publication.

Let's first give the values that are derived: Pre-symptomatic 0.9, i.e. a part of 0.9 of of the R0 value two, symptomatic transmission has a part of 0.8 and then environmental transmission 0.2, asymptomatic transmission 0.1. If you add these four values together, you get two again.

If you now look at the figures, you will see that the overall pre-symptomatic transmission share is 46 percent of the total transmission activity. It is a similar figure from what we discussed a few days ago from another working group, from another paper.

The value R0 of two is apparently good news. Because when we get a R0 of two, [rather than higher other literature estimates] then we have less [transmissions] that must be reduced to reduce the R0 below one and thus also to bring the epidemic to get a standstill.

However, if you now realize that 46 percent of all this transmission activity takes place before the symptoms, it will of course then again be very difficult to reduce these transmissions. Because you can only isolate symptomatic patients. These considerations are now being fed into an interesting calculation that wants to find out: What can actually be done with certain interventions to detect an infected person?

How long does it take to detect it? And how many have been infected by the infected person in this time, because 46 percent of the transmission happens before the symptoms start? And because it also takes some time before a diagnosis is made after the onset of symptoms and then for the contacts to be identified.

A very important number plays a role in this, namely the serial interval of the infection, which has been recalculated here, which actually tells us: Even if one isolates immediately at the beginning of the symptoms, i.e. immediately removes a symptomatic person from the transmission situation, then not only has he already infected people, but these people who are subsequently infected are themselves also already contagious at the time when the first patients show the symptoms.

We have actually already observed something like this in the Munich case tracking study and were surprised by it. But now there is, in principle, quantitative evidence, which really backs up the whole thing with numbers and rates, that this is actually happening.

Difference between manual and automatic tracking

Christian Drosten:
The main outcome of the study is that you are too late with a simple [manual] identification of cases and contact tracing, because the whole thing depends on identifying symptomatic patients. So it really comes down to the last day. ...

In other words, here it is calculated in a formally very correct way and very robustly on the very latest figures, that from a certain point in time of the epidemic, targeted diagnostics plus case tracking plus isolation of contacts cannot stop this epidemic. This is no longer possible.

What you can do to stop such an epidemic is to simply do a lockdown. Then you don't have to track cases, everyone will be at home. You can of course do a combination of measures where you say there is a lockdown, which is a bit milder. Like the contact ban. ...

So here [the study] conceives a hypothetical App. This App can record the symptoms at the onset of the symptoms - so you just type it into your mobile phone: I have symptoms now. Then the App says: Okay, I've already sent the data you sent to the lab. That means the App can already do the registration for laboratory diagnostics. In principle, you can be diagnosed immediately - the App itself triggers the diagnostic process.

Then the information about this diagnosis, if it is positive, will be included. And at that moment, the App can start to trace back which other mobile phones were in your vicinity. Of course you can also tell how long the contact should be and so on. ... And these holders of the other mobile phones are then informed. "You were in contact with a patient during the infectious period of that patient".

And you can say in a nutshell, if the epidemics ran at the same speed as in the beginning in Wuhan and if 60 percent of the case identifications via the App were successful (which means, you have to realize, that if 60 percent of the population would install such an App and if then again about 60 percent of those who are informed that they should stay at home actually stay at home), then you could already lower R0 below one. This is amazing.

There are a few caveats on that. It is then said that in reality the speed of propagation in Europe is already faster than it was at the beginning in Wuhan. There are certainly several reasons for this. Population density, behaviour of the populations, but also how far the infection has already progressed. This of course makes it even more difficult again, so that a higher degree of cooperation among the population is actually needed. ...

But it is achievable, it is an achievable goal to use such apps to make these inevitable time delay in reporting activity to bridge the gap. To communicate the essential information "You have been in contact with an infected person, you should get tested now" and the time you gain there, that would actually do much more or almost the same as a real lockdown - under this mathematical model.

Then there are a few follow-up effects and a few possible opions. One possibility, for example, is that in a "high incidents situation" - a place where there's a very serious epidemic going on, or at a time when there's a wave of infections - you could bring even more speed into the whole system by saying we're going to leave out this testing stuff. We're reprogramming this App now. If I check this box now, I have symptoms, the App doesn't tell me: "Okay, I've already signed you up with the lab for testing," but the App says: "Okay, we see you as positive now.

Anja Martini:
Then I'll stay home.

Christian Drosten:
Right. Anything symptomatic is now defined as positive without testing. This is, of course, an intervention measure, that this criterion is aggravated.

Combining the App with other measures

Christian Drosten:
Of course you have to say that you could combine such an App, for example by other general factors that reduce the transmission of the infection, such as wearing masks. This is of course not included here, because we do not know exactly how much wearing masks could perhaps reduce the overall transmission activity if everyone wore a mask, and there are no estimates of the numbers. But it is conceivable that this combination of a mask, if everyone wears it in society, if it has an effect, that this effect will be added to such a finely controlled App.

And that is a real prospect. In this public discussion, which is of course already going on at the moment with some desperation: How do we exit these measures? And what do we do next?

I'm fascinated by the thought that such an App, especially if many would participate, would provide us with an instrument to achieve a completely different subtlety of control and to be able to say that normal life can go on.

There is no general lockdown. Companies can work, schools can teach, everything can work, but not for everyone at all times. There will come a time when you have this message on your mobile phone: "Please go into home quarantine. If you could then show this and your employer would say: Well, that's how it is, home quarantine this week. Then I find, that is at least a very interesting model one should not refuse thinking about.
At the end of the interview Drosten comes back to the App and emphasises another advantage:
And to think about such smarter measures that are really feasible and which, by the way, can even be implemented in poor countries, where lockdown does not work the same way, but where everyone still has a mobile phone in their pocket. Of course, we must think about this and set an example.

What can you do for your immune system?

Anja Martini:
Quite a lot of people also ask themselves again and again: Can we do more? For example, can we do something for our immune system and build it up? Maybe vitamin C, vitamin D. You got any ideas? Can you do that? Running?
Christian Drosten:
So of course it is always good to have a good immune system. And of course, it's always good to be fit as a fiddle. Surely it's not the case that you will immediately be infected by running in the park, just because you encounter other people. That's certainly not something to worried about, going outside and running. This, you can, I think, recommend.

But that's where it stops.

What you can say is to stay away from people who might be infected. Right now that would just be anybody you meet, for example when you go shopping or something.

There is this rule in the USA that says: Six feet, six seconds. So six feet apart and six seconds of contact, you should take that as a rule. So that you keep this minimum distance and don't stay so close to somebody for so long. That's probably such a good way of thinking when moving around in public places.


Other podcasts

Part 28: Corona Virus Update: exit strategy, masks, aerosols, loss of smell and taste.

Part 26: Corona Virus Update on Vaccines: clinical trials, various types, for whom and when.

Part 23: Corona Virus Update: need for speed in funding and publication, virus arrival, from pandemic to endemic

Part 22: Corona Virus Update: scientific studies on cures for COVID-19.

Part 21: Corona Virus Update: tests, tests, tests and how they work.

Part 20: Corona Virus Update: Case-tracking teams, slowdown in Germany, infectiousness.

Part 19: Corona Virus Update with Christian Drosten: going outside, face masks, children and media troubles.

Part 18: Leading German virologist Prof. Dr. Christian Drosten goes viral, topics: Air pollution, data quality, sequencing, immunity, seasonality & curfews.

Related reading

This Corona Virus Update podcast and its German transcript. Part 27.

All podcasts and German transcripts of the Corona Virus Update.

The study in Science Magazine on the impact an App could have: Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing

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