According to a new study by Japanese researchers, the coronavirus survives on the skin about five times longer than the influenza virus. But what is actually behind the new findings?
It is said that flu viruses can survive on the skin for 1.8 hours, whereas the Covid-19 viruses survive for no less than 9 hours. Disinfecting can kill both corona and flu viruses within 15 seconds. Nevertheless, frequent and especially proper hand washing is important to contain the spread of Covid-19.
To better understand this study, we asked an expert of LTS for her professional opinion and got the following answer.
What does the expert say?
To begin with: from a scientific point of view, the study has been thoroughly executed. The skin model used was well conceived according to our expert. Fresh skin was utilized, i.e. “corpse skin”, which was not older than 24 hours. Furthermore, the skin was incubated in a physiological medium for the duration of the experiment. What does this mean exactly? The skin was moistened from one side with a liquid similar to the composition of blood in order to resemble reality as closely as possible.
Incubation time and temperature
On the other hand, there were also aspects concerning the execution of the study that should be questioned. On the one hand, the incubation time of a test series was up to 96 hours. This is very long, since even fresh skin no longer possesses all enzymatic activities after this time, for example the triggering of the immune response. Secondly, temperature is a parameter that could distort the results. The “ex vivo” skin used was only tempered to 25°C when the experiment was performed, but the skin surface temperature is normally 32°C. Thus, it is likely that enzymatic activities are slowed down or inhibited. The control group, which had flu virus solution applied in droplets on their hands, was “incubated” in a room at 25° C, but this does not change the skin surface temperature. The bottom line is that under real conditions, even the coronavirus could have been detectable for a shorter period of time.
Choice of solvent
Another aspect that can be questioned is the choice of solvent used for production of the viral droplets. On the one hand, a physiological but artificial buffer was used for the study, and on the other hand, coughed-up mucus (sputum) from the upper respiratory tract of various test subjects. It would have been advisable to carry out the study also with saliva or secretion from the mouth pharynx of the test subjects, since normally in case of droplet infection the virulent amount is transmitted in this secretion. Saliva itself, in addition to having slightly acidic properties, also has several specific enzymes that differ in composition from those in the sputum of the upper respiratory tract. Thus, saliva would have been a good additive to reflect the real conditions in the experiment.
A matter of perspective
Finally, it is important to note that the study tested only influenza type A viruses for comparison – though this is the most common cause of influenza, it is also the one with the shortest half-life of the viruses. In conclusion, the nine hours mentioned by the study, during which the coronavirus could survive on the skin, do not necessarily correspond to reality. Upon closer examination of the study, the time difference in survival compared to other viruses may not necessarily be as great as one might expect based on the main statement. However, it is a fact that by observing the rules of hygiene we can protect ourselves and our fellow human beings from diseases.
Thus, the following still applies:
- always wash your hands thoroughly,
- keep distance and
- ventilate regularly, especially in winter!
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