David Fisman Profile picture
Professor, interested in plagues, pestilences and politics. "One of the most dangerous Canadians"-- Ontario MPP (sic) Randy Hillier
Tricia Profile picture papillon4444, rabble-rousing crone 🇨🇦 🌈 🍎😷☮️ Profile picture Su An Profile picture RacyO. Ghost 👻 stories and HAYSTACKS. Profile picture A_Typical_Psychiatrist Profile picture 20 added to My Authors
17 Jan
Israel's reproduction number appears to have declined rather sharply in recent days, with around 25% of the country vaccinated, and some additional percentage having at least partial immunity via prior infection. Image
As noted previously, Israel is the country to watch for herd effects from the Pfizer vaccine because of its small population, small geographic size and rapid rate of immunization. We may be seeing this now.
A press-reported Clalit study that reports 33% vaccine efficacy after 14 days in over-60 year olds might seem surprising and disappointing, and in line with Peter Doshi's recent suggestion that Pfizer may have overstated vaccine efficacy in their trials.

Read 9 tweets
15 Jan
An observation on schools and COVID-19. In both Ontario and BC, there is what I will call a "magical unicorn" narrative related to schools and COVID-19. In these provinces public health officials repeatedly assert that SARS-2 transmission in schools occurs rarely, or not at all
Cases occurring in students and teachers are (without rigour, without systematic testing in schools, without the use of phylogenetic analysis) asserted to have been acquired in the surrounding community.

These provinces have not controlled their epidemics well.
In Atlantic Canada, epidemics have been controlled very well. Indeed, on a per capita basis, cumulative epidemic size in BC (despite low testing rates/high positivity) is 9.4 x that in Atlantic Canada. Ontario's epidemic is now (per capita) 13 x that in Atlantic Canada.
Read 11 tweets
12 Jan
Four points to make re: @SteiniBrown ’s presentation

1. This is a clear demonstration of how critical communication is to pandemic control.
2. We have a tsunami of deaths coming. I am so sorry. The “casedemic” rhetoric directly contributed to this tragedy, and I hope there are consequences for this who knowingly pushed disinformation.
3. @SteiniBrown is presenting near term epidemic curves that rise and rise. Their fall, if symmetrical, means that we can double the deaths on the way back down.
Read 6 tweets
7 Dec 20
This is a key point. We REALLY need to know that we have good surveillance infrastructure in place for novel vaccine technologies. We haven't used mRNA vaccines at the population level before; nor have we used adenovirus vaccines at scale.
The major issue with vaccine "phase 4" surveillance is mis-attribution of effects via a "post hoc ergo propter hoc" logical fallacy. Just because someone gets an illness after a vaccine doesn't mean they got the illness FROM the vaccine.
My favorite example from my AMOH days...was asked to sign off on a report from an individual who had tripped and chipped a tooth after being vaccinated. This was listed as a vaccine adverse effect.
Read 17 tweets
2 Dec 20
Interestingly there really is something to the idea that individualism vs. collectivism worsens ability to control covid. This is a very simple log-linear regression looking at the Hofstede individualism index vs. cases per million in late November. Red is model fit.
These countries differ in a lot of other important ways; you can run this with GDP, corruption perception index (corrupt places are doing better!), Gini coefficients...but those other indices seem to fall out of the model, and Hofstede stays in.
This is obviously ecological, caveat emptor. Lots of other things we could adjust for: testing rates, age structure, infectious disease vulnerability index (which has basically been invalidated by covid :)), but there's certainly suggestion of a collectivism/individualism effect.
Read 5 tweets
28 Nov 20
I am not sure what’s up with all the angsting about test characteristics of rapid tests. Worried about low specificity and false positives? Repeat the test and only consider repeat positives to be positive.
Worried about sensitivity and false negatives? Test twice and consider negative only if 2 tests are negative.
Tests are just tools to sort something into piles, with each pile enriched in the attribute you’re looking for
Read 8 tweets
26 Nov 20
Ontario will apparently ram through the extension of Dr. Williams' appointment at CMOH in the legislature today, some time around lunchtime.
Thanks to the AG's report, we now know that Dr. W is likely valued by the Ford government BECAUSE he is a weak and ineffective CMOH.
Moving forward, their comms strategy will be to frame any criticism of Dr. W's disastrous leadership as "personal attacks", so watch for that.

Here's my list of 11 reasons why Dr. W needs to be removed as CMOH. I'm sure there are more. These are factual, not personal.
1. Failure to acknowledge community transmission in March, which contributed to widespread hospitalizations and LTC outbreaks

2. Failure to deal promptly with the LTC crisis though the scope and likely toll of the outbreak were obvious by early April
Read 11 tweets
23 Nov 20
This is a great question. Here’s my response

The idea of vaccines is to get you to immunity without having to go through the risk and discomfort of illness, and without you passing through a state where you are an infectious case that creates other cases.

With vaccines we can actually eliminate disease.

Natural immunity doesn’t eliminate disease at the population level, because rising immunity pushes down R, which makes the current outbreak end but means the disease will resurgences when we re-accumulate sufficient susceptibles
Read 7 tweets
20 Nov 20
Reupping, because I was asked about Ontario ICU forecasts this morning, and want to walk folks through how to use this tool.
Many caveats as per usual:

1. This is a pre-print, currently under peer review. It may b wrong.
2. This isn't a mechanistic mathematical model; it's a simple statistical model.
3. Because I just made this it's not validated (events to validate or invalidate haven't occurred).
Though it does display good "convergent" validity with publicly available ICU occupancy estimates, as well as those from CCS and CIHI.
Read 24 tweets
17 Nov 20
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.
Read 31 tweets
13 Nov 20
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 20
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 20
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 20
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 20
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 20
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
13 Oct 20
This (as with the Quebec karaoke superspreader event) is extremely difficult to explain without invoking aerosol. High viral load in resp mucus of the index case (asymptomatic) created a superspreader event.

It would be extremely interesting if the index case was the instructor: prolonged shouting/exhorting during a spin class would make sense in terms of aerosol generation...is that info out there?
Events like this are literally showing us the gateway out of this situation. It is distressing to see that institutional public health across Canada is still reluctant to acknowledge the importance of aerosol: costing time, money, lives now.
Read 4 tweets
12 Oct 20
I had some wonderful back-and-forths with @aatishb about this and it’s fantastic to see the finished product on “math of masks” at

There is a wonderful YouTube video here:

If you want a mathy-er version of same, we have an approach using next generation matrices which you can access here (and which we’ll cover this week in chl5425 at @UofT_dlsph)

Read 4 tweets
10 Oct 20
Thanks to the friend who reached out to suggest that having my own dedicated troll army suggests that our messaging and information are effective. That's a nice shot in the arm.
With that in mind, I'll use this account to disseminate good info on what's happening with covid...and hopefully drive the trollbots crazy.

Let's start with covid in Canada today:
R(t) by province...note New Brunswick is the place with a qualitative change in status, and is few days into a LTC outbreak after a few months of elimination of local trans.
Read 8 tweets
7 Oct 20
@LeaferReefer_ @BogochIsaac Getting to herd immunity via disease transmission vs. getting to herd immunity via vaccination are very different.

For disease transmission, you cross the susceptibility threshold for transmission when fraction immune = 1 -(1/R0). Let's say R0 for covid is 2; that means you...
@LeaferReefer_ @BogochIsaac hit that threshold when (1-(1/2) = 50% of the population is immune. In Canada, that's at 20 million infections.

x 0.7% IFR = 140,000 deaths.

And at 50% immune, R = R0 x S = 2 x 0.5 = 1. R hits 1 at the PEAK of the epidemic curve...so you still need to come down the other side
@LeaferReefer_ @BogochIsaac of the epidemic curve. As these curves are somewhat symmetrical, once you hit that threshold, you still have 10's of thousands of deaths to go, and the final epidemic size is much greater than 50%.
Read 9 tweets
7 Oct 20
I learned so much at a panel on administrative law, decision making & the precautionary principle at @OsgoodeNews this morning. I learned about the legal process related to excellent MOH Shanker Nesathurai's push to keep migrant workers safe.
Superior court found fault with Health Services Appeal and Review Board opinion striking down limits on bunkhouse occupancy, noting that "precautionary principle" (making well-reasoned decisions out of abundance of caution even when there is uncertainty) is explicit in HPPA.
HPPA = Health Protection and Promotion Act, which is Ontario's major public health statute.

I wonder whether this same argument could be made in support of Dr. DeVilla's push to end indoor service in bars and restaurants. If not, why not?
Read 4 tweets