In this podcast the director of Charité Berlin's Institute of Virology Prof. Dr. Christian Drosten provided his assessment. I assume he is referring to this paper and translated the relevant podcast section with deepl translator.
(pp. 2-3; German text).
Christian Drosten: There is this one study, which you mentioned on Friday, on the stability of the virus. There is a working group that took this virus and compared it with the old SARS virus, for example, how it is stable on objects. And so according to the motto, how it sits on the door handle and how long it will remain infectious there. I believe that this paper, this contribution, has been very well communicated in the social media.
Anja Martini: Up to three days, it says on plastics or stainless steel, on a door handle or something. On paper it can be active up to 24 hours. Is there any truth to it?
Christian Drosten: Yes, exactly. It's relatively difficult to handle such data in practice. The impression I get when I read it is that it expresses relatively long times. That it is said that two days on surfaces is infectious and so on. And that is perhaps also presented a bit as if that was particularly bad. Unfortunately, it is just like that, especially in scientific short articles, that this mood prevails in some media, that it is said: Bad news sells particularly well. If you take a look at the data in this paper, it is not at all clear how much virus was applied to these test surfaces and in what form. It simply says that virus was applied to the surface. But it is a big difference whether this virus is in a large or a small drop of liquid - or in a drop that has almost no volume at all. If you look at what is being done, you take a surface, which can be made of plastic or paper or metal, and you probably put a drop of virus solution on it. And then you take that back. We say you resuspend it. So you put it back into a new fluid and you put it on a cell culture. That's a test to see if the virus is still infectious. Then you can also determine how much infectivity is still there at any given time by dilution experiments. And then it is already the case that after 48 hours infectivity can still be detected on this surface, i.e. that there is still infectious virus in the cell culture. But it is just very, very little. You start with almost 10,000 infectious units and in the end there are significantly less than ten infectious units. The question is, of course, when you get this on your finger and on your mouth, is there anything infectious left? This thins on the finger again and then comes into contact with the acidic environment of the skin. This is actually what we should know from such a study, and this cannot be simulated in such simple experiments.
And the conclusions that are drawn from it are very quickly misunderstood. This is more a technical study. If you take a closer look, you will see that it is true that cell culture can still become infectious after 48 hours. But the time in between is already covered in these experiments - and there you can see that there is a very rapid decline in all these experiments. No matter which surface was covered with virus, after only eight hours, i.e. between eight and 24 hours, there is no longer any measured value. But in this interval, the infectiousness of the virus drops very rapidly, practically on all surfaces in the same or similar way. And my suspicion is that this eight hours is actually the time in the experiment before this small liquid droplet of virus has completely dried out. That this has nothing to do with the surface itself, but that it is simply the drying out of the virus. And is of course completely different in a real situation. For example, when we cough in our hand - there is virus sticking to our hand. When we reach for a door handle, the volume of liquid, the film of liquid that sticks to the door handle, is almost impossible to measure. It dries much faster than the droplet that is brought to the surface in the laboratory. And the question is of course also: what kind of droplet is it anyway? A cell culture medium is really not the same as coughing up mucus and saliva. That is why we have to be very careful with such scientific data. They are not wrong. But they are so simple that they probably don't reflect the real infection. And it's very difficult, because something like that will probably be published visibly, so that it also triggers press reports. If the press then says: alarm, the virus can be kept on surfaces for two days, then perhaps a false impression is created.
The people who want to protect themselves also set the wrong priorities. They say, "Help me. I won't touch a doorknob anymore. But if I get close to anybody, I lose sight of that. But of course, the more important mechanism of such viruses that can be transmitted via droplet infection is that you should not get so close to each other, that you should not cough, that you should not have long speech contact with other people. Of course there are contact transmissions via surfaces, door handles and other things. But now that you're putting numbers on it, I think that distorts your idea of reality. And we all need a healthy and realistic assessment at the moment - if we try to organize our daily lives well and protect ourselves from infection. And therefore the better assessment is: Someone coughs up the virus or has a wet mouth - then the virus stays in the air for a short time before and around these people and then falls to the ground relatively quickly.
Anja Martini: A short time, 20 minutes, ten minutes?
Christian Drosten: Yeah, something like that. It's not much longer, and that varies, of course. It will be longer when coughing than when speaking, because the droplets when coughing are much smaller and they can float longer. And then at some point there is also such an equilibrium, a balance, between a drop that is so small that it can stay in the air for a long time. But which is so small that it dries out very quickly. And the virus is then no longer in a liquid and is then destroyed because it dries. All these things we don't know for this virus. And until we have measured them in really precise scientific studies, we should rather let a little bit of general knowledge about other cold viruses be brought in. Such headlines of scientific articles, which are quite justified and which carry a lot of truth in them, but you should not shorten them and then think, now the whole assessment has suddenly changed.