A lot has happened in the past year, so you can be forgiven for not having a clear memory of what some of the main concerns were at the beginning of the pandemic.
However, if you think about the beginning of the pandemic, one of the main concerns was the role that surfaces played in the transmission of the virus.
As an epidemiologist, I remember spending countless hours responding to media requests, answering questions like whether we should wash the outside of food cans or disinfect our mail.
I also remember seeing teams walking the streets all day, cleaning poles and cleaning public benches.
But what the evidence in reality say about surface transmission over 12 months in this pandemic?
Before addressing this, we need to define the question we are asking. The main question is not whether surface transmission is possible or whether it can occur in the real world – it almost certainly can.
The real question is: what is the extent of the role of surface contact in the transmission of the virus? That is, what is the probability of capturing COVID through a surface, as opposed to other transmission methods?
There is little evidence that superficial transmission is a common way of spreading the coronavirus. The main form of propagation is through air, either through larger droplets through close contact, or through smaller droplets called aerosols. As a side observation, the relative role that these two routes play in transmission is probably a much more interesting and important issue to clarify from a public health perspective.
One of the best comments on the COVID surface transmission was published in the newspaper Lancet Infectious Diseases in July 2020 by Emanuel Goldman, professor of microbiology in the United States.
As he described it, one of the motivators for the exaggerated perception of the risk of superficial transmission was the publication of a series of studies showing that SARS-CoV-2 virus particles could be detected for long periods on various surfaces.
You probably saw these studies because they received huge publicity around the world and I remember doing a lot of interviews in which I had to explain what these discoveries really meant.
As I explained at the time, these studies could not be generalized to the real world and, in some cases, the media releases that accompanied them tended to overstate the importance of these findings.
The main issue is that, as a general principle, the time required for the death of a population of microorganisms is directly proportional to the size of that population. This means that the greater the amount of virus deposited on a surface, the longer you will find viable viral particles on that surface.
Therefore, in terms of designing experiments relevant to public health, one of the most important variables in these studies is the amount of viruses deposited on a surface – and how close that is to what would happen in the real world.
If you understand this, it becomes apparent that several of these virus survival studies have increased the chances of detecting viable viruses by depositing large amounts of viruses on surfaces much larger than would be reasonably expected to be found in the real world. In addition, some of these studies have customized conditions that would extend the life of viral particles, such as adjusting humidity and excluding natural light.
Although there was nothing wrong with science here, it was the relevance of the real world and the interpretation that was sometimes wrong. It is notable that other studies that more closely replicated real-world scenarios found less impressive survival times for three other human coronaviruses (including SARS).
It is important to note that we are relying on indirect evidence to assess the role of coronavirus surface transmission. That is, you cannot really do an ethical scientific experiment that confirms the role that surface transmission plays, because you would have to infect people deliberately. Despite being an apparently so straightforward question, it is surprisingly difficult to determine the relative importance of the various transmission routes of this virus.
Instead, what we have to do is examine all the evidence we have and see what it tells us, including case studies that describe transmission events. And if we do that, there will not be much support for surface transmission, being of great importance in the dissemination of COVID.
We need to put the risks of exposure to SARS-CoV-2 through the various modes of transmission in perspective, so that we can focus our limited energy and resources on the right things.
This does not mean that surface transmission is not possible and that it is not a risk in certain situations, or that we should ignore it completely. However, we must recognize that representations of the transmission of the threat surface are relatively small.
We can therefore mitigate this relatively small risk by continuing to focus on hand hygiene and ensuring that cleaning protocols are more in line with the risk of surface transmission.
In doing so, we can potentially save millions of dollars spent on obsessive cleaning practices. They are probably bringing little or no benefit and being realized only because they are easy to do and provide the guarantee of doing something, thus alleviating some of our anxieties.