David Fisman Profile picture
17 Nov, 31 tweets, 6 min read
A thread...great news on the vaccine front this week, but perhaps a good time to remind folks that this is NOT the new normal, and that pandemics have a beginning, a middle and an end. We are in the middle now; the end will come.
I want to map out for you, in the most general terms, what I think is the likely future contour of the pandemic globally, based on how remarkably constant GLOBAL case growth has been for a number of months now.
Caveats galore.

As either Neils Bohr or Yogi Berra said: "Prediction is hard, especially about the future".

I think Neils Bohr but more fun if it was Yogi.
So, absent a crystal ball, and also knowing that no good deed on the internet goes unpunished, I'm going to share the following because: [drumroll] I think it is important for people to understand that what we are experiencing is not indefinite/open ended.
Ok, here goes...

Something that's interesting (again, GLOBALLY) is that since April, global growth has basically been log-linear. In other words, you put it on a log scale and it's a straight line.
I think that represents the fact that (however reluctantly) people know how to control this now, so countries oscillate between wanting to scale back control and needing to institute control because they're in crisis (that's Canada right now).
That nets out at an R around 1.1, with very little variation over the long haul. Here's a graphic from something @AshTuite and I made in February, a lifetime ago, but which we are still updating [art-bd.shinyapps.io/nCov_control/]
What's nice about this is that you can see that we are basically growing 0.2 log per month, so the point where attack rate exceeds 50% of the global pop can be predicted by extrapolating.
[this is log10, btw]
If transmission heats up over the winter and R does rise that just means we get there sooner. 50% of the globe's pop is around 3.5 or 4 billion; the case count we hit when we have 4 billion infections depends what fraction of cases are identified...
It's probably somewhere between 1:10 and 1:20, or was back in May when I made this figure. Maybe it's higher now because of more widespread testing; maybe it's lower now because of more widespread disease. Maybe it nets out.
It doesn't make a huge difference...log 10 is between 8.3 and 8.6. That would mean we'll hit 50% infected when we're at 200-400 million counted cases. Unfortunately that's not too far away.
We're at 55 million now (log10 = 7.7 or so); with constant R we're growing by 0.6 million per day, and that is increasing over time (because R > 1). At 0.2 log per month, that is somewhere between 3 months at the low end and 4.5 at the high end.
This graph shows global R and doubling time on cumulative cases...both remarkably constant for some time now.
Here's the same R, but with moving average daily cases superimposed...R ~ 1.1 is a mighty force, and we're surpassing 600,000 cases a day now.
But back to the flawed prognostication: this puts global infections at 50% by late winter or early spring. The fixation on 50% infected is because with R in the 2's, that's where (globally) we'll hit the point where R effective is around 1, even without intervention.
That means the epidemic peaks and starts to decline. At that point there are a lot of PREVALENT infections, so this gets carried forward for a while like a truck that's come downhill and continues forward under its own momentum even on the flat...
..., so lots of deaths coming and hospital resources still needed, but declining over time. It'll be further helped along if we see vaccine rollout around the same time (as we will, it's now clear).
Even in the absence of a highly effective vaccine, this is where the thing starts to turn into an endemic (likely seasonal) disease. That would again put us on a 1918 timeline in terms of the worst (in terms of transmission) being behind us by April 2020.
R hovering around 1 without intervention also makes any interventions that are in place much more effective (anything we do markedly decreases growth).

Numerous caveats here...
Some caveats: this is a global average, so there'll be heterogeneity. Places that have prevented covid better (Atlantic Canada, NZ, Australia, pacific rim generally) may be more vulnerable to resurgences.
But I'm not that worried. The vaccines (plural) will backstop, and anyway, the good places seem to be able to keep being good (yay, path dependence!).
It's a weird disease, and I'm sure we'll see things like industrial clusters and nursing home and cruise ship outbreaks for a while, as we do with flu, but the massive global impact will wane. Perhaps vaccine will be highly effective against infection as well as disease...
...uptake will be universal, and this will become our third eradicated disease? (Smallpox, rinderpest). Let's hope so.

In the longer term (multi-decadal), this is not (in my opinion) going to be a major threat, or certainly not greater than many other virulent pathogens that coexist with us.

A pandemic is different because of universal susceptibility.
Large scale prior immune experience, ageing out and dying of older individuals, replacement of susceptibles via loss of immunity and births will turn this into a (likely seasonal) disease with high attack rates in those without immune experience...
...in other words, what we already see with flu and RSV. And hopefully, as above, a highly effective vaccine will make elimination/eradication possible (TBD).
Many of us have been wrong a lot over the last 9 months, but at this point I think the virus has shown its hand and it basically looks like 1918, but with overdispersion of R, and with coronavirus rather than flu.
It's very much on a 1918-19 timeline, and we are controlling it with 1918-1919 interventions (we think we're so smart...they were smart too, and I think a bit less smug).
Anyway, I think we have this long and ugly winter to get through. The appropriate course of action right now, as Manitoba is showing the rest of Canada, is to aim for #CovidZero, because if you don't, the virus is in the driver's seat, and you lose.
Hope that's helpful to people. Stay strong...we need to get through this winter. And if we have lousy leadership, we need to pressure that leadership with everything we've got to help them make good decisions that protect us all, not just friends and donors.


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More from @DFisman

13 Nov
New with Steve Drews and Sheila O’Brien from @CANBloodServ and the amazing @AshTuite

Infection fatality ratio for covid-19 in Ontario. Tldr: it’s around 1% after excluding longterm care deaths, same estimate as in many other countries.

Here is the major take home:
We digitized the figure from @GidMK @BillHanage et al’s brilliant work (medrxiv.org/content/10.110…) and overlaid Ontario age specific IFR. Our axis labels have been chopped off.
Read 6 tweets
5 Nov
Ontario's @NDP table a bill that would ensure independence of the CMOH and transparency of public health responses during public health crises.

It's a no-brainer that would help all of us, so I assume it'll have an uphill battle. 😃.

Encore: merci a @nickelbelt pour ayant fait ca.
To the friends who have pointed out that we have previously had CMOH's recommend unwise courses of action (e.g., de facto criminalization of HIV infection):

yes, there needs to be a mechanism to remove underperforming CMOH's even in a crisis.
Read 4 tweets
30 Oct
Schools are also an upstream enabler if the rest of our economy in a way that bars, gyms and restaurants are not.
Look, I’ve been saying for months now that schools are the one mass gathering it’s hard to cancel.

We don’t want to close them. That’s why reducing class sizes is so critically important.
Looking at data, our hospitalizations and icu’s are surprisingly flat in Ontario. I get that this sucks for people in affected businesses, but the closures are targeted, and many of the outbreak hotspots aren’t close-able.
Read 12 tweets
26 Oct
Asked by a friend to comment on the reasonableness of the IHME forecasts for Canada (30+k deaths by Feb). (covid19.healthdata.org/canada?view=to…). The IHME model is impressive...
And again, based on the 2nd (winter) wave of the pandemic ahead of us, and given that we currently stand around 10k deaths, the projection of 30k deaths by February seems reasonable. Note my earlier tweet about 2:1 ratio of 2nd to 1st wave in 1918/1919.
What's impressive to me in IHME is the forecast that we would/could save 10,000 Canadian lives in the months ahead with a national mask mandate. This, again, seems reasonable, based on best available data.
Read 8 tweets
25 Oct
Global R(t) has been remarkably stable since the first wave. Here it is plotted against global doubling time. Will try to unpack this further when I get a chance but it’s a good news/bad news story: many infections ahead, but this isn’t open-ended.
“Moving average” = 7 day moving average for doubling time.
Just to unpack this a bit, there's a direct relationship between R and doubling time, inasmuch as R(t) is a function of growth rate, as is doubling time. Doubling time may just be a bit more intuitive.
Read 12 tweets
24 Oct
This is amazing. We're headed into the second wave of a once in a century pandemic. Ont and Qc have been backstopped by the feds. Now here come the Cons with a motion to initiate a massive AUDIT of the public health response? Now? October 2020?
Like, THIS is when you're going to tie up PHAC, Procurement, Health Canada, not to mention the companies the govt is working with to procure vaccines and tests, with what looks to be the audit from hell?

Because PHAC, Health Canada, and every other federal office/bureau/department isn't already hanging on by their fingernails trying to build systems, structures and responses to protect Canadians?

Now? Really?
Read 10 tweets

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