A lot has happened in the past year, so you could be forgiven for not having a clear memory of what some of the main concerns were at the start of the pandemic.
However, if you think back to the start of the pandemic, one of the major concerns was the role that emerges in the transmission of the virus.
As an epidemiologist, I remember spending countless hours answering media requests and answering questions like whether to wash the outside of food cans or disinfect our mail.
I also remember seeing teams of people walking the streets at every hour to sweep poles and clean public benches.
But what is the evidence really say about the transmission of more than 12 months to the surface in this pandemic?
Before we tackle this, we must define the question we are asking. The main question is not whether surface transmission is possible, or whether it can happen in the real world – it almost certainly can.
The real question is, to what extent does surface contact play a role in the transmission of the virus? That is, how likely is it that COVID will be captured through a surface, unlike other transmission methods?
There is little evidence that surface transmission is a common way of spreading the coronavirus. The main way it is spread is through air, either through larger droplets through close contact, or through smaller droplets called aerosols. As an aside, the relative role these two pathways play in transmission is probably a much more interesting and important question to clarify from a public health point of view.
One of the best comments on COVID surface transmission was published in the journal Lancet Infectious Diseases in July 2020 by Emanuel Goldman, a professor of microbiology from the United States.
As he described, one of the drivers for the exaggerated perception of the risk of surface transmission was the publication of a number of studies showing that SARS-CoV-2 virus particles could be detected on different surfaces for a long time.
You’ve probably seen these studies because they got massive publicity around the world, and I remember doing numerous interviews where I had to explain what these findings actually meant.
As I explained at the time, these studies could not be generalized to the real world, and in some cases the media reports that accompanied them tended to exaggerate the importance of these findings.
The main point is that as a general principle, the time it takes for a population of microorganisms to die is directly proportional to the size of that population. This means that the more virus deposits on a surface, the longer you will find viable virus particles on that surface.
So in terms of designing experiments relevant to public health, one of the most important variables in these studies is the amount of the virus deposited on a surface – and the degree to which this matches what would happen in the real world.
Understanding this, it becomes clear that some of these virus survival studies stack the opportunity to detect viable virus by depositing large amounts of virus on surfaces far greater than what could reasonably be expected in the real world. In addition, some of these studies have modified conditions that would extend the life of viral particles, such as adjusting humidity and excluding natural light.
While there was nothing wrong with the science here, it was the real-world relevance and interpretation that was sometimes wrong. It is noteworthy that other studies that mimic more realistic scenarios found less impressive survival times for three other human coronaviruses (including SARS).
It is important to note that we rely on circumstantial evidence in assessing the role of surface transmission for the coronavirus. That is to say, you can’t actually do an ethical science experiment that confirms the role that surface transfer plays, because you should intentionally infect humans. Despite being such a seemingly simple question, it is surprisingly difficult to determine the relative importance of the different transmission routes for this virus.
What we should do instead is look at all the evidence we have and see what it tells us, including case studies describing transmission events. And when we do this, there isn’t much that supports surface transmission, which is of great importance in the spread of COVID.
We need to put into perspective the risks of exposure to SARS-CoV-2 through the different modes of transmission, so we focus our limited energy and resources on the right things.
This is not to say that surface transfer is not possible and that it does not pose a risk in certain situations, or that we should ignore it completely. But we must recognize that the transmission of threats to the surface is relatively small.
We can therefore mitigate this relatively small risk by continuing to focus on hand hygiene and ensuring that cleaning protocols better reflect the risk of surface transfer.
By doing this, we can potentially save millions of dollars spent on obsessive cleaning practices. These are likely to offer little or no benefit and are only done because they are easy to do and provide the reassurance to do something, relieving some of our fears.