In response to a question about evidence that surfaces are not spreading the virus:
Good question, I wondered whether I should write more about it then. I think one's prior beliefs/priorities matter a lot here, so let me be explicit about mine first. I think there's a limit to how many precautions people will follow, especially over the length of time we need to stop this pandemic. The more things we ask people to do, or the more complex they are, the less likely they are to be followed. And if people stop following some guidelines and nothing bad happens, they will be more likely to stop following other, more important ones too. So it's important to focus efforts on getting people to follow a few important and simple guidelines for the sake of general compliance. At the individual level, it can be perfectly rational to go beyond these guidelines. With that as preamble:
Essentially nobody challenges the idea that transmission by fomites (particles on surfaces) is possible. The question is whether it happens in the real world, and at a frequency that's high enough for us to mandate/suggest specific actions. The WHO considers fomites to be a plausible mode of transmission, but their report also states: "Despite consistent evidence as to SARS-CoV-2 contamination of surfaces and the survival of the virus on certain surfaces, there are no specific reports which have directly demonstrated fomite transmission". Their communication of scientific evidence has been poor, so I looked into what epidemiologists & virologists were saying, especially on Twitter. After months of contact tracing around the world (albeit much less than ideal), I've encountered discussion of only 3 cases where transmission by fomites (particles on surfaces) may be more plausible than other explanations, and that's being generous (see first Twitter thread below). Even these cases are very far from certain. And infection rates within households seem to be lower than one would expect if surfaces were important for transmission.
Since it's hard to show a negative, there's no paper I can point you to which spells this out clearly, or states precisely what the relative risks of surfaces vs. droplets/aerosols are - the numbers are still unknown! But the specialists have generally downgraded their perceptions of the risk of surface transmission, though they hedge their public statements appropriately. See the articles & tweets linked below.
Three caveats: (a) it's a hard topic to study, so it's possible that fomite transmission has happened where contact tracing has been unsuccessful, (b) fomite transmission may have been incorrectly attributed to aerosols in spaces like offices, and (c) since hand-washing and sanitising was one of the major initial recommendations, we may have stopped transmission via fomites in the real world. If we ease up on that, it may start to happen.
Despite those caveats, I think that the balance of evidence so far suggests that surfaces are not important. I understand the desire to take precautions, but personally don't sterilise things I bring home, and did not do this even when the risks were higher here. I have recommended to concerned family that they could consider just leaving things on a balcony for a while if they wanted to be very safe. Virus numbers on plastic decrease by a couple of orders of magnitude in two days in cool, dry conditions; it's much faster when warmer and more humid, and on most other surfaces.
[I've linked to a few papers below, but they seem less helpful than they appeared. I found the threads on Twitter more helpful because they were to the point and open to immediate challenge from other experts.]
Papers:
https://www.nejm.org/doi/full/10.1056/nejmc2004973 (can survive on surfaces)
https://msphere.asm.org/content/msph/5/4/e00441-20.full.pdf (...but decays faster at higher temp & humidity)
https://academic.oup.com/.../doi/10.1093/cid/ciaa905/5868534 (hospital surfaces have viral RNA but no viable viruses found)
https://www.thelancet.com/action/showPdf?pii=S1473-3099(20)30561-2 (much-publicized commentary, not the most useful, I think)
https://wwwnc.cdc.gov/eid/article/26/9/20-1798_article (suspected fomite transmission, weak evidence and could well be aerosols)
https://wwwnc.cdc.gov/eid/article/26/6/20-0412_article (suspected fomite transmission, weak evidence and could well be aerosols)
https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e1.htm... (suspected fomite transmission, weak evidence)
Articles:
https://www.who.int/.../modes-of-transmission-of-virus... (WHO report mentioned above)
https://www.krisp.org.za/.../StAugustinesHospitalOutbreak... (hospital outbreak in which physical contact or fomites are suggested but without much evidence, see page 20) ". Summary at https://www.sciencemag.org/.../study-tells-remarkable...
https://www.cbc.ca/.../coronavirus-surfaces-groceries... (general article, several experts offer their opinions)
Tweets:
https://twitter.com/DiseaseEcology/status/1279097818351726592 (good thread summarising the best known case while highlighting its rarity)
https://twitter.com/Bob_Wachter/status/1263673015591530496
https://twitter.com/CathNoakes/status/1282230720778457088
https://twitter.com/firefoxx66/status/1260905943933620226 (see rest of the thread too)
https://twitter.com/TheBinderLab/status/1254166676515454978
https://twitter.com/LucyStats/status/1282112670230106112 (contrary opinion)
UPDATE a week later: A recent Atlantic article on the topic summarises this pretty well: https://www.theatlantic.com/ideas/archive/2020/07/scourge-hygiene-theater/614599/
It does lean a bit on that commentary piece that I thought was not very helpful (among other things, it misrepresents the goals of the papers on rate of viral decay on surfaces). But that's a minor weakness.
Good question, I wondered whether I should write more about it then. I think one's prior beliefs/priorities matter a lot here, so let me be explicit about mine first. I think there's a limit to how many precautions people will follow, especially over the length of time we need to stop this pandemic. The more things we ask people to do, or the more complex they are, the less likely they are to be followed. And if people stop following some guidelines and nothing bad happens, they will be more likely to stop following other, more important ones too. So it's important to focus efforts on getting people to follow a few important and simple guidelines for the sake of general compliance. At the individual level, it can be perfectly rational to go beyond these guidelines. With that as preamble:
Essentially nobody challenges the idea that transmission by fomites (particles on surfaces) is possible. The question is whether it happens in the real world, and at a frequency that's high enough for us to mandate/suggest specific actions. The WHO considers fomites to be a plausible mode of transmission, but their report also states: "Despite consistent evidence as to SARS-CoV-2 contamination of surfaces and the survival of the virus on certain surfaces, there are no specific reports which have directly demonstrated fomite transmission". Their communication of scientific evidence has been poor, so I looked into what epidemiologists & virologists were saying, especially on Twitter. After months of contact tracing around the world (albeit much less than ideal), I've encountered discussion of only 3 cases where transmission by fomites (particles on surfaces) may be more plausible than other explanations, and that's being generous (see first Twitter thread below). Even these cases are very far from certain. And infection rates within households seem to be lower than one would expect if surfaces were important for transmission.
Since it's hard to show a negative, there's no paper I can point you to which spells this out clearly, or states precisely what the relative risks of surfaces vs. droplets/aerosols are - the numbers are still unknown! But the specialists have generally downgraded their perceptions of the risk of surface transmission, though they hedge their public statements appropriately. See the articles & tweets linked below.
Three caveats: (a) it's a hard topic to study, so it's possible that fomite transmission has happened where contact tracing has been unsuccessful, (b) fomite transmission may have been incorrectly attributed to aerosols in spaces like offices, and (c) since hand-washing and sanitising was one of the major initial recommendations, we may have stopped transmission via fomites in the real world. If we ease up on that, it may start to happen.
Despite those caveats, I think that the balance of evidence so far suggests that surfaces are not important. I understand the desire to take precautions, but personally don't sterilise things I bring home, and did not do this even when the risks were higher here. I have recommended to concerned family that they could consider just leaving things on a balcony for a while if they wanted to be very safe. Virus numbers on plastic decrease by a couple of orders of magnitude in two days in cool, dry conditions; it's much faster when warmer and more humid, and on most other surfaces.
[I've linked to a few papers below, but they seem less helpful than they appeared. I found the threads on Twitter more helpful because they were to the point and open to immediate challenge from other experts.]
Papers:
https://www.nejm.org/doi/full/10.1056/nejmc2004973 (can survive on surfaces)
https://msphere.asm.org/content/msph/5/4/e00441-20.full.pdf (...but decays faster at higher temp & humidity)
https://academic.oup.com/.../doi/10.1093/cid/ciaa905/5868534 (hospital surfaces have viral RNA but no viable viruses found)
https://www.thelancet.com/action/showPdf?pii=S1473-3099(20)30561-2 (much-publicized commentary, not the most useful, I think)
https://wwwnc.cdc.gov/eid/article/26/9/20-1798_article (suspected fomite transmission, weak evidence and could well be aerosols)
https://wwwnc.cdc.gov/eid/article/26/6/20-0412_article (suspected fomite transmission, weak evidence and could well be aerosols)
https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e1.htm... (suspected fomite transmission, weak evidence)
Articles:
https://www.who.int/.../modes-of-transmission-of-virus... (WHO report mentioned above)
https://www.krisp.org.za/.../StAugustinesHospitalOutbreak... (hospital outbreak in which physical contact or fomites are suggested but without much evidence, see page 20) ". Summary at https://www.sciencemag.org/.../study-tells-remarkable...
https://www.cbc.ca/.../coronavirus-surfaces-groceries... (general article, several experts offer their opinions)
Tweets:
https://twitter.com/DiseaseEcology/status/1279097818351726592 (good thread summarising the best known case while highlighting its rarity)
https://twitter.com/Bob_Wachter/status/1263673015591530496
https://twitter.com/CathNoakes/status/1282230720778457088
https://twitter.com/firefoxx66/status/1260905943933620226 (see rest of the thread too)
https://twitter.com/TheBinderLab/status/1254166676515454978
https://twitter.com/LucyStats/status/1282112670230106112 (contrary opinion)
UPDATE a week later: A recent Atlantic article on the topic summarises this pretty well: https://www.theatlantic.com/ideas/archive/2020/07/scourge-hygiene-theater/614599/
It does lean a bit on that commentary piece that I thought was not very helpful (among other things, it misrepresents the goals of the papers on rate of viral decay on surfaces). But that's a minor weakness.
