I keep getting asked about the possibility that sars-cov2 will be with us for a long time (many of the questions are driven, I think, by Chris Murray’s statement that we won’t simply “put this behind us”). I do think it is likely to become a seasonal, endemic virus
At least for a long time to come. That’s because (a) the virus has show an ability to move from humans to animals and back again (mink) and (b) eradication is hard, even with good vaccines and disease w/o animal reservoirs (polio, measles).
And yet I’m optimistic about a non-reckless return to normalcy over the medium turn. Why?

As noted previously, pandemics have a beginning, middle and end. Even in the pre-microbial era, they end. Remember the great pandemic of 1925? No, because there wasn’t one. But by around 1922 the terrifying pandemic of 1918-19, thought to have killed around 40 million: over
Where did influenza H1N1 disappear to?

It didn't go anywhere. The descendants of devastating 1918 H1N1 continued to circulate as seasonal influenza until 1957. An H1N1 strain threatened to cause a pandemic in 1976, and we had a mild pandemic of a novel H1N1 in 2009.
Co-circulation of H1 strains with H3 strains has been common since the 1990s. H1 is the "mild" flu virus.
[NB severity of flu is a spectrum, and as a clinician I have seen tragic situations, including respiratory failure and death, from H1 and influenza B. Get your flu shot!]
But the reason 2009 was a mild pandemic? Those most likely to die conditional on infection (older people) were born pre-1957, and had substantial immune protection from early life exposure to related H1N1 strains (that were dominant when they were kids)

Which brings us to the difference between a pandemic and a seasonal epidemic caused by a respiratory virus. Might influenza have attenuated by 1919? It seems mortality in wave 4 of that epidemic (autumn 1919) had declined. But the major change was in population susceptibility.
We tend to be very focussed on *the bug* with pandemics. What really creates a pandemic is widespread susceptibility.

Does the discarded cigarette butt start the forest fire? Sure. But what makes the forest fire a conflagration is having a long drought and a lot of dead trees
A discarded cigarette butt in a forest that's wet from rainfall doesn't have the same impact.

Same with us and pathogens. When a novel pathogen is introduced into a totally susceptible population, and it has an R0 > 1 (each old case makes > 1 new case), we are dry tinder.
And if we don't put it out fast a conflagration occurs.

If we don't change behaviour, then the R(effective) for a communicable disease is approximately R0 x S (the fraction of the population susceptible).
As we acquire immune experience, R(effective) drops, whatever else we are doing or not doing. In this pandemic, that immune experience can be acquired via prior infection, or (and hopefully increasingly) via immunization.
The epidemic peaks when R(effective) hits 1, and declines thereafter, as each old case makes < 1 new case before going away.

Note that this applies under conditions where there's no control, no behavior change, etc. Very different from our current reality.
But the basic idea is that the pandemic itself seals its own doom by depleting population susceptibility, just as a forest fire ensures its own end by burning up all the fuel.

And it overshoots: so by the time the pandemic is over, the R(effective) is LESS than 1.
So: game over for the virus, right?

Erm, no. That decline in R is transient. Susceptibility in the population starts to reaccumulate, both because of waning immunity in infected/vaccinated individuals, and because of accumulation of newly minted baby-people in the pop
who replace the elder-people at the other end of the life span as they die. That results in repletion of susceptibility. The virus (as with flu, as maybe with sars2) can also lend a helping hand by mutating over time (we call this "drift") with flu, and becoming...
...sufficiently different from previously circulating strains that it de facto increases population susceptibility.

We see this play out every year or two with very drifty flu. It's one of the reasons we have to keep changing the flu vaccine (which has 2 different A antigens)
But that's not a pandemic, for two reasons:

1. We have a much lower R because of prior population immune experience.

2. Those who have been around longest (older people) have prior immune experience.
And are protected against these resurgences by earlier exposure. That's why the 2009 pandemic was mild. Those who would be most likely to die from a novel resp infection had prior lifetime immune experience. Not the case in 2019-2021.
So be confident. The idea of a forever-pandemic is about as plausible as the idea of a forever-forest fire. Not gonna happen.
Viruses replicate a lot faster than we do, so they always have a head start on anything that depends on mutation. It is likely that we'll challenges over time as novel variants, maybe even vaccine escape mutants, emerge.
And I would expect that even with immunization we will continue to see seasonal and off-season outbreaks of covid-19 in crowded institutional settings (and cruise ships) which have been hotspots for outbreaks long before there was a COVID-19 pandemic.

I hope that's helpful.
There's more to say here, but it's coffee time.

COI declaration: I study infectious diseases for my job, and I think it's dumb for people to die of communicable diseases unnecessarily.

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More from @DFisman

5 Feb
So the identity of the @originandclever twitter account (now deleted) has been positively identified. It belongs to a junior physician in central Ontario. I am not going to doxx them on twitter.
But I would like to take a bit of a walk down memory lane in terms of some recent nastiness from this recently graduated physician, writing under the cover of presumed anonymity.
I don't know if this needs to be looked at by @cpso, @UofTFamilyMed, @McMasterU, @UHN or other organizations this person has been affiliated with in recent years...would love to hear what others think. If journalists want more info, my DMs are open.
Read 25 tweets
3 Feb
This is right on.
There is substantial excess mortality right down to age 15.
Absolute death numbers are smaller because baseline deaths are lower
Here’s the most recent estimate I’m aware of.


We need to know what fraction of excess mortality in young adults is opioids.
In older adults in the US covid mortality and excess mortality are essentially 1:1

This is a fantastic paper from @AnnalsofIM that reminds us to standardize populations so we make fair comparisons.

Read 4 tweets
2 Feb
@DonaldWelsh16 Oh hello.

I knew Dr Rorabeck. He was a wonderful guy. @SchulichMedDent does have much to be proud of. Like any institution, it has its warts.
@DonaldWelsh16 @SchulichMedDent But to respond to your comment: I think you’re referencing the concept of balanced pathogenicity, which probably will will, over the longer term, favour less virulent strains.
@DonaldWelsh16 @SchulichMedDent The difficulty we have with VOC is that they appear to bind better to ace2 (as a vascular biologist I bet you’ve heard of that!) and that may underlie their increased infectivity and increased
Read 9 tweets
2 Feb
The blizzard of distraction coming out of @fordnation and his assorted flying monkeys is by design. It’s a comms strategy. They need to distract you from:

1. Botched vaccine rollout
2. Massive death toll in long term care
3. Muddled and confused back to school plan
4. Political interference with hospitals and health advocates
5. The Mysterious Case of the Missing Rapid Tests
6. Unspent billions in federal pandemic funds
7. Huge excess risk of covid in those with low income and people of colour in Ontario
8. Failure to institute basic measures like paid sick leave
9. Utter lack of transparency on public health decision making
10. Full ICUs, need for field hospitals and transferring patients 100s of km for care
Read 5 tweets
2 Feb
Spent the evening working with a colleague on new variant epidemiology in central Ontario.

It is worth being concerned. The R's for old variants and SGTF are divergent, with old variants < 1 and new variants still > 1, and gaining relative market share at 8% or so per day.
If that constant growth continues we'll be around 50% SGTF by the end of February.
Note new variant R is not high; around 1.1 at the moment. But it has been consistently 40% higher than old variant R. We are going to need to do better, at a time when everyone is weary, ICU's are already full up, and kids are heading back to schools.
Read 4 tweets
1 Feb
I'd be curious what others with more experience in the innovation/commercialization world think, but it seems to me that we don't want to go back to the type of "vaccine nationalism" we had when Connaught was a crown corp or a @UofT-owned entity. The world has changed a lot
Given the tremendous resources and quality control that you need in order to compete on the world stage in vaccines, the two streams would be:
1. Lots of support for Canadian startups with great ideas (e.g., Medicago) that allows them to expand and compete, but also...
2. Making Canada a really attractive place to do vaccine science, and working with the big global players (Pfizer, GSK/Sanofi, Moderna now, Merck, J&J, etc etc) to make us a hub for research AND manufacture
Read 7 tweets

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