Today’s topic is about INFECTION. (Please note that this is primarily an opinion piece where I write about things I’ve learned and things I suspect)
This is a tricky topic because we only know so much about how COVID-19 is transmitted, in terms of specifics. But we do have a pretty good general idea, and I want to talk a little bit about stuff we know, and what we can infer from that knowledge, and how it relates to you, me, and people in general as life goes on.
For the purposes of this post, please assume that I’m talking about our situation here in the lower mainland, and perhaps all of BC, but not beyond, and certainly not the US or other countries.
When people talk about how contagious a virus is, they usually refer to the r0 value. The r0 value is what tells us how quickly the virus spreads. An r0 of 1 means that every infected person will in turn infect 1 other person while they are contagious. An r0 of 2 means they will infect 2 people, and those 2 people will each infect 2 people, and so on and so on in exponential growth. An r0 of 0.5 on the other hand means that 2 infected people will result in only 1 additional infected person. So to simplify, an r0 of <1 would mean that the virus will eventually die out. This is the situation that we want.
Early on in COVID-19’s spread, before any restrictions or guidelines were put in place, it was generally said that the virus had a peak r0 of 3.6 in Canada. This is a fairly high infection rate, and means outbreaks could explode quite quickly if not controlled immediately. Now that number is heavily averaged, so many places will have had much worse infection rates, and others would have seen much lower infection rates. The important thing to take away is that the r0 was >1.
Since that time, BC has put a number of restrictions in place, including but not limited to: Physical distancing, quarantining presumptive cases, and contact tracing followed by isolation for those who have been potentially exposed. And between March and May, we have finally begun seeing some very real improvements in our infection numbers. I’m happy to report that we have hit the point where our r0 for COVID-19 in BC is generally <1 now. In fact, Canada’s r0 is now hitting that important <1 point! (see attached graphic).
Today, BC has a total of 307 known active COVID-19 infections, a significant drop from previous months, and a number that has consistently been dropping for a little while now. It’s very encouraging!
Now I’d like to talk a little about why I think we can keep this forward momentum going, even with some relaxing of restrictions.
COVID-19 is spread through a couple of different ways. It can be spread through coughing/sneezing minuscule droplets containing a viral load, which can be taken into your body through mouth, nose or eyes (including via fingers). There’s the possibility of it being transmitted through semen as well, and we also know it can be found in stool. But not sweat or tears, so we’ve got that at least!
Over the past few months there have been a number of studies aimed at looking at viral load, infection, and surfaces. I read one in particular that gave pretty compelling testimony that in most cases, a surface left for 24 hours should be safe to touch. This is based on how much of the virus was left on different surfaces (cardboard, paper, plastic, different metals, etc) for periods of time. But it’s important to note that it is not ANY amount of viral load that can lead to infection, it must be in sufficient amounts. At this time, we do not know that exact amount, and it probably varies to some degree based on people’s immune systems (this last bit is my assumption).
The viral load needed to produce a new infection is a very important thing to try to understand though, even if we can’t know the exact specific volume. But we do have a way of gauging it:
We know that a saliva test (cheek swab) is not enough to test positive for COVID-19 reliably. In fact, the nasal swab at the back of the throat is not entirely reliable, which is why many places require 2 consecutive negative results before declaring someone clear. This tells us that in most cases breathing on someone (or walking into someone’s breath), while gross, is not by any means a guarantee of infection. In fact, it may take many deep exhales, or coughs or sneezes to excrete enough of the virus to be a threat. And this theory can be backed up by the previous r0 of 3.6 when we did not have any restrictions in place. If simply breathing on a person in passing was enough to transmit the virus, we would have seen a much higher infection rate! But where we do see those multiple infection breakouts, it’s always situations such as families in a shared home, old folks homes, prisons, and work environments where distancing is impossible and people spend hours next to each other exhaling and sneezing and potentially building up a larger volume of viral load over time.
I have not heard of a single instance of infection through public transit. There have been extremely few and very isolated reports of cases of infected people at grocery stores, and I haven’t seen any information in those reports that would make me assume the person was infected at the grocery store and not at home or elsewhere. I also have not heard of a single outbreak of multiple infections (or any additional infections) after a person at a grocery store was discovered to be infected.
And I think I know why that could be. In addition to the likely need to build up a sufficient viral load in order to infect someone, and the speed at which the virus dies when on various surfaces, there is also the mathematical fact that any given viral load on a surface will not transmit completely when touched by another object. For instance, if there were 10 “drops” of virus on a box of cereal, and someone put there hand on them to pick up the box, those 10 “drops” of virus would be split between the hand and the box. If that person then touches their cell phone with their hand, some more of those “drops” will transfer to the phone, leaving less behind on the hand. If that person then pokes themselves in the eye, will there still be enough viral load to infect them? I don’t have that answer, but math would tell us that the chances of it occurring decreases with each touch.
So between low saliva viral loads, reduced viral volume over touched surfaces, viral death over time on surfaces, and heck even just the wind dispersing the virus quickly across too great an area to be a threat, we are in a very good place right now… even with relaxed restrictions.
So I would encourage everyone to breath a little easier, I think we’re going to be ok. We should do our best to really focus on preventing prolonged exposure in enclosed spaces with high volumes of people. Short rides on buses or skytrains with some distancing space, and even more so with an open window, should be ok. Grocery shopping should be ok. Don’t cough in people’s mouths. Don’t french kiss strangers. Etc etc. (edit: avoid heavy breathing in enclosed spaces, such as singing practice, nightclubs, or physical activities indoors).
I do need to say though that I am NOT a scientist, I am NOT an expert, and I am not formally educated in any area specific to this topic. I am just trying to take things we know, and make what I hope are logical conclusions based on this knowledge. I welcome thoughts and feedback.
That’s all for now, stay safe everyone!