This graph in a nutshell is what the experience of my home province of Ontario has been with Covid-19. You can click on the graph to view it full size.
I have actually merged two graphs together here and added the orange lines. The top graph if of the “Rt” value of Covid-19 in Ontario and is produced by an Ontario Statistician, Ryan Imgrund. The bottom graph is the 7 day average of reported daily new Covid-19 cases in Ontario as compiled by CTV.
Let me first explain to you what you are seeing, why it is important, and what you can do about it.
The R value of a virus is its rate of transmission. R0 is the rate that it is transmitted if no preventative measures are put in place. That is, how many other people (on average) will one person with the virus infect. With Covid-19, the R value is estimated to be somewhere between 2.5 and 3. If no preventative measures were in place each person with Covid-19 would infect on average about 2.7 people.
To illustrate how significant that number is: If you start with 1 person, after 10 rounds of transmission you end up with 20,000 people infected. After another 10 rounds of transmission you end up with 400 million people infected. This is why we saw such initial rapid growth looking like an exponential graph, because the growth was exponential.
This graph, however, is displaying the Rt number. This is the effective transmission rate of the virus. The transmission rate of the virus can be mitigated by preventative measures. Each addition of a preventative measure reduces the Rt value. Each easing or removal of a restriction increases the Rt value. The key number is the number one. If that Rt value is greater than one, the number of daily cases will continue to grow, if it is less than one the number of daily cases will eventually shrink to zero.
So in the top graph, we can see some of the preventative measures (in red) and some of the relaxing measures (in green).
School closures drastically reduced the Rt value. This was not only because the students stopped interacting, but parents started working from home. It took some pretty drastic steps to get that initial value under one. Not only did we have school closures, but all but essential businesses were closed, then the list of essential businesses was restricted greatly. Finally around April 14th the Rt value dropped below one for the first time.
Note how their is a lag between the first and the second graph. The number of cases in the 2nd graph don’t peak until 10 days later. That is because this graph is of the dates that the cases were reported. People however are reporting cases about 10 days on average after they are infected.
There is another interesting thing that you will see in the graphs, and I have tried to highlight with the orange lines. Generally speaking, every time the Rt value passes through zero you get either a peak or a valley in the number of cases. Cases rise (with a 10 day lag time) when the number is above one, and decline when the number is below one. When is passes through one it is the point at which it is no longer rising or declining and so you get a peak or valley in numbers.
You can see from the graphs that for the most part after the initial clampdowns were initiated, Ontario was able to keep its Rt number under one for most of the next four and a half months. Hence the significant decline in cases per day.
Ontario’s reopening plan has four stages. I won’t go into the details here, but you can look it up. Each stage is more permissive than the previous one. There is an interesting interplay of events happening here. You would expect that as Ontario’s businesses and events opened up, the Rt value would start to go up, but largely that didn’t happen. Why? People started wearing masks. Along with more and more people wearing masks, Ontario municipalities started implementing mask by-laws. This mitigated the impact of businesses opening up and kept the Rt number in check.
By the end of July just about everyone was wearing a mask indoors in public.
So why does the Rt value start increasing at that point, and why do we see the number of cases starting to rise?
Because once everyone is masked, there is not available benefit to be gained from additional people masking. There are no additional people masking. There is not additional downward pressure that is being placed on the Rt value.
Instead we see businesses continue to open, people eating more inside restaurants, churches being a little bolder in relaxing restrictions, friends being a little more lax about how many they socialize with, people returning to office jobs, schools reopening.
While not shown on the graph, the Rt value in Ontario has continued to climb. On August 30th it was at 1.21, the highest point at which it has been since the state of emergency was declared back in March. I am expecting it to continue to climb because of the reasons mentioned above.
Returning to school, in Ontario and elsewhere, is a giant social experiment that I believe is going to have rather severe repercussions.
So what can we do?
Here is what I would encourage each and every one of us to do. Stay a step behind the allowed activities: If you are allowed a social bubble of ten, restrict yourself to five. Want to go back to the office? Continue working from home (if possible) a little longer. If your church is not currently meeting, but is considering meeting again, ask for it to be delayed two or three more months until we start to see the impact of schools reopening. If your church is allowed 50 percent capacity, ask that it stay restricted at 30 percent. Consider home schooling (and I never thought I would hear myself say or write that!)
In short, do what you can to keep your own personal number of contacts with others down. Every little bit that we do helps to bring down that Rt value.
I realize that their are people out there who are struggling, and businesses out there that are struggling. Look for ways to assist them in ways that does not have any measurable impact on the Rt value. Order takeout if you are financially able. Give an encouraging call to someone who is socially isolated. And by all means look after your own mental health. Get as much fresh air and exercise as you can. And don’t be afraid to talk to someone you trust. You are not alone in going through this.
As usual your thoughts and comments are welcome.