[COVID-related. Cross-posted from Grand, Unified, Empty. Sorry I couldn't make the graph embed work here, you can see the original at a readable size on my blog.]
This is not the COVID post I thought I would be writing a few weeks ago. I honestly didn’t think I’d be writing a COVID post at all.
A few weeks ago, most of Canada seemed to be under control. There were a few hot spots left in e.g. Southern Ontario, but almost any other graph you looked at showed a nice, clean downward trend. How quickly things change. I live in Ottawa, so I’m going to focus there. This data comes directly from Ottawa Public Health (though the graph is mine):
You can see things getting consistently better in May, staying quite steady throughout June, and then starting to creep back up around the beginning of July.
This is a huge problem.
It may seem like I’m exaggerating slightly – after all, Ottawa (a city of 1 million people) went from roughly 4 new cases a day, to roughly 8 new cases a day, over the span of two weeks. That hardly seems comparable to the huge surges being seen in the southern United States or other problem areas. Ottawa’s health care system and hospitals have plenty of capacity. Our testing turn-around time remains under 48h, and our testing throughput remains high. We have a mandatory mask bylaw in place. There seem to be a lot of things going right.
In point of fact there are a lot of things going right – I’d still rather be in Ottawa than in any part of the US. But just because some things are going well, doesn’t mean we’re not still in trouble. Going from 4 to 8 new cases a day is an increase, and any increase is really bad news.
At the risk of rehashing a topic everybody is sick of at this point: virus spread is modelled exponentially (this exponent is the “R0” everybody keeps talking about). R0 isn’t a magical fixed value; when something changes (e.g. people start wearing masks) then R0 for the virus changes too. When R0 is less than one, the virus gradually fades out of the population, as was happening in Ottawa in May. When R0 is exactly one, then the number of new cases stays flat, as was happening in June. When R0 is greater than one, the virus starts picking up steam and spreading again.
R0 in Ottawa is, clearly, greater than one at this point, and has been since roughly the beginning of July (or maybe a little later, depending on how much you’re willing to smooth the graph). This isn’t a big deal for today – we can still handle 8 new cases a day, or 10, or 12. But the thing about positive exponential growth is that it keeps going up, faster, and faster, and faster. As a very rough approximation, let’s assume that the last two weeks are representative of R0 in Ottawa right now, and that our new cases continue to double every two weeks. That would mean that August 1st we’d be dealing with 16 new cases per day. Not too bad. By the end of August, 64 new cases a day – bad (until very recently we had fewer than 60 active cases total), but still manageable. By the end of September though… 250 cases a day, which is probably more than we can handle. And so on. If the trend continued through to Christmas (which is, granted, very unlikely) then we’d be looking at roughly 16000 new cases a day.
Now there’s a lot of reasons we’re very unlikely to hit 250 cases a day, let alone 16000. If new cases increased that much I assume the city would re-institute some kind of lockdown, and at that kind of load other factors like herd immunity would start kicking in as well. But when cases are already increasing it seems like a really bad time to start reopening even more. And yet…
The general consensus seems to be that there’s a minimum of two weeks of lag between the development of actual cases, and reporting. This time accounts for how long it takes somebody who’s been exposed to incubate the virus, develop symptoms and go get tested. Of course in some places where testing is overloaded, the delay can be much more than that, but Ottawa is not overloaded, so let’s assume two weeks.
Ottawa officially entered “phase 2” of our reopening on June 12th, though in practice most businesses were not ready on the day of, and reopened piecemeal over the following week; let’s take an average reopening date of June 15th. Two weeks after that brings us to June 29th, which is, (surprise!), right at the beginning of our uptick in cases. This is a bit of evidence that our “phase 2” reopening was in fact too much; R0 is now back above one, and the virus is spreading.
In worse news, despite phase 2 already being too much, Ottawa officially entered “phase 3” of our reopening yesterday (July 17th). Not only does this seem like a bad idea in general given that R0 is already back above one, but phase 3 includes a huge swath of very risky activities whose impact on R0 will almost certainly be far greater than the impact of phase 2: indoor service at restaurants and bars, movie theatres, museums, etc. As with phase 2, a lot of businesses weren’t ready day of; if we take an actual phase 3 reopening date of July 20th, and add two weeks, it’s easy to see an even bigger spike of cases coming down the pipe, starting around August 3rd. (August 3rd is a statutory holiday here, so in practice I expect the data might not show up until a few days later.)
The one bright spot in all this is that Ottawa made masks mandatory while indoors, starting July 7th. That will presumably have a big impact on transmission rates, and was less than two weeks ago, so we won’t see it in the data yet. Hopefully new cases start to drop again around July 21st (two weeks after mandatory masks), and if we’re very lucky then that decrease will entirely counter-act the increase from both stage 2 and stage 3 reopenings. But that seems like a lot to ask, especially since many people were already voluntarily wearing masks even before the mandate. Only time will tell.
Ultimately, I predict continued increases in Ottawa until around July 21st, at which point the trend will reverse due to mandatory masks, and we see decreases again until August 3rd or shortly afterwards. Then we’ll see the impact of phase 3 reopening, but I can only imagine that it’s going to be bad. I suspect by late August it will be clear that phase 3 is unsustainable and will have to be rolled back. I only hope we don’t learn that lesson too much the hard way.
[This section is more of an appendix of other little things I didn’t fit in the main post.]
Somebody I discussed this with argued that I’m reading too much into the graph I presented. The data from end of June up to July 9th actually looks well in line with the rest of June, and the growth after that point could very well just be random variance as was likely the case with the brief spike from June 7th to 13th. I suppose this is possible, though it feels unlikely to me. Time will tell, if cases continue to rise or not.
Alberta and BC (two other provinces) are also seeing recent spikes in cases after reopening, though oddly Ontario (the province that Ottawa is actually in) has not. I haven’t dug into the regional data to back this up, but I imagine it’s because the Peel region and the other “hot spots” I referenced earlier are finally under control and decreasing rapidly, which is balancing out the gradual increase in Ottawa and other places. Again, time will tell. I expect we’re already at the bottom of that particular wave, so Ontario-wide cases should start ticking up again (slowly) this week.