by Raywat Deonandan, PhD
Epidemiologist & Associate Professor
University of Ottawa
(I add my credentials to these COVID-19 blog posts in case they get shared. I want readers to know that my opinion is supposedly an educated and informed one)
Welcome to your new normal. We are a few days into uncharted waters for our species: a global pandemic, with many countries in near literal lock down or compelled isolation. Businesses are failing, relationships are fracturing, workers are losing their jobs, and everyone is panicking at least a little.
But we mostly did it. We’ve “socially distanced” ourselves to slow the spread of the disease in order to prevent overwhelming our health care system, lest we go the way of poor Italy. And when I say “we”, I mean most of Canada. I see that other countries in a similar stage of the epidemic are not being as vigilant.
So now what? How does this all end?
Well, regardless of what happens next, it eventually ends in only one way: global herd immunity. The two questions that remain are: how long will it take to get there, and at what price –human and economic?
What is Herd Immunity?
First, let’s be clear about what we mean about herd immunity. Imagine a herd of cattle walking along a valley. The infant calves and weak members are in the middle of the herd. The young and strong bulls lead from the front, with other strong members patrolling the periphery. If any predator were to threaten the herd, that threat would be dealt with by the strong ones at the periphery. The ones on the inside not only never have to encounter the predator; they never even have to know that the predator was ever there!
So in population health, we try to make a proportion of the population immune to a disease so that the non-immune never have to encounter the disease in the first place, as they are metaphorically in the middle of the herd.
The proportion of a population that needs to be immune before herd immunity kicks in depends on many properties of the disease. For Small Pox, for example, we needed 80% to eradicate that monstrous thing. And we achieved it. For COVID19, I’ve heard estimates of 60-70% immunity necessary to achieve herd protection. This will vary from country to country; but 60-70% is the last global estimate I’ve heard.
How does a population become immune? Two ways: vaccination and recovery from infection.
While modern biotechnology can sequence a virus’s DNA and crank out vaccine candidates in a matter of days, it realistically takes 1-2 years to refine, test, mass produce and distribute that vaccine. Maybe with an unprecedented global effort, we can get that down to just under a year, but I wouldn’t bet on it. Several candidates are already being trialed.
So maybe with a Manhattan Project level of commitment, we can get that time frame down to under a year. It can’t be faster than several months, as it takes that long for a test population to experience the disease cycle. Add on mass production and distribution requirements and the task gets lengthy indeed.
Mind you, all of this is predicated on the assumption that human beings do indeed become immune from COVID-19 after having recovered from the disease, or after having been vaccinated. It’s unclear if this has indeed been demonstrated.
Let It Burn
One approach (supposedly initially endorsed by the British government), is to let the disease “burn through” the population. Infected people would recover in 2-4 weeks and acquire immunity that way.
But let’s work through the numbers in Canada. We have about 37 million people living here. To achieve herd immunity, we would need something like 60-70% of the people to become infected and recover. So let’s assume the low end. That means about 22 million infections are necessary.
Now, if we let the disease have its way with the population, those infections would happen quickly. In fact, the most conservative observed doubling rate of the disease is 6 days. We would therefore see 22 million infections in about 2 months.
Do keep in mind that COVID19 has a duration of 2-4 weeks. So almost all of those 22 million people will be in the throes of the disease at the same time.
Now, based on the Chinese experience, about 15% of cases require hospitalization. The proportion seems to be higher in Italy. So let’s use the conservative Chinese data. Applied to Canada, that would mean about 3 million people would require hospitalization in a 2 month span.
Canada has 57,000 hospital beds. That’s it. Without hospital care, the majority of that 3 million would die. But to be conservative, let’s say 25% would die. That’s 825,000 dead Canadians in 2 months… just from COVID19.
Note that is in line with the global CFR (case fatality rate) for this disease, which is presently 3.4%. For 22 million cases, that means about 750,000 deaths. But CFR is a function of health system capacity. So if all the beds are filled, our CFR would be much higher.
That doesn’t include the people dying from strokes, heart attacks, and traffic accidents who would otherwise have lived had there only been space in the hospital.
So I hope you agree that that option is off the table.
The path we’re on now is a long term one. I have news for you: for this to work, this is our new normal. I threw together a very quick and dirty model of what it would take to get Canada’s rate of production of COVID19 cases to a sustained slow simmer:
The above was created using Gabriel Goh’s free data visualization engine. What it shows is that if we get the reproduction number (which is the number of people that one infected person can infect) from the current 2.5 down to 0.35, then our total number of hospitalized cases holds at around a non-newsworthy 72 persons.
This would happen at around the 40th day of isolation, according to this model. But that is extreme isolation, closer to quarantine.
Getting the reproduction number down to about unity (i.e., one infected person infects only one other person) or a bit less would take us beyond the peak of the wave toward a managed case load at about the 2 month mark in theory. Do keep in mind that this model is based on a butt load of assumptions, and was thrown together quickly and without a lot of nuance.
It doesn’t matter, because my point is this: isolation, or social distancing, or whatever you want to call it, keeps the case load down to a manageable number…. while wreaking havoc on our economy, our social lives, and our mental health.
So what happens at the 2 month mark? Well, according to this and many other models, we begin a staged re-entry into our previous lives, with a lot of care…. because it’s coming back. The disease is not gone, it’s just simmering in a few bodies.
Cases will rise again, probably 2-4 months after the end of the current wave. So then we will have to go into isolation again for 2 months or so.
Rinse and repeat until the vaccine is ready.
Get ready, because this is our future. It’s why my girlfriend has been trying to cheer me up for the past couple of days, as I’ve stared at the epidemiology curve and watched my portfolio and social life dissolve in real time.
It’s why I kind of wish I were Jared Leto, blissfully unaware that anything’s going on.
But China Has Recovered!
Yes, China is doing much better. They began their extreme isolation procedures at the end of January and are seeing the epidemic pass on a similar timetable that my model above shows (though mine is fit to the Canadian population, not Chinese).
The Chinese enacted procedures that I think would be challenging to replicate here in Canada.
And unless the virus has mutated, I believe it will return to the affected areas of China sometime in the next few months, at which point they will enact lock down procedures again.
In other words, until 60-70% of humanity has gained immunity, or until the virus mutates into non-lethality, I believe we will have to be on guard for it for the foreseeable future…. until that vaccine arrives.
The entire world will likely be pursuing this costly but necessary policy of waves of suppression (via isolation) followed by relaxation for at least a couple of years.
Tell Me More About Mutations!
Coronaviruses live in non-human animals. This one experienced a mutation that allowed it to infect a human being. Then it mutated again, which allowed it to move from humans to other humans.
It seems to have mutated again, as the type that attacked China is not the same that is ravaging Europe, according to this person. I’m not a geneticist, so I can’t comment on that.
One of the prevailing theories of how and why the Spanish Flu went away is that it eventually mutated itself into irrelevance. From an evolutionary point of view, it makes sense. A pathogen’s best bet for long term survival is not to kill its hosts. So over a long time, environment selects for those mutations that are less lethal. And while that might happen to the virus causing COVID-19, it also might not.
What Else is Possible?
Well, there is another option. Imagine if the whole world were to decide, as one species, to quarantine itself for 30 days. Hospitals would still be open, and food would be supplied. But all of humanity would not not interact physically with anyone else for 30 days.
(UPDATE: My 30 day estimate is based on one study. But it might be closer to 60 days from first exposure to complete clearance of the virus.)
Those who have the disease would either recover in that time, and be immune afterwards (assuming, again, that recovery causes immunity). Those who are infected and don’t know they are infected would have the same experience, but would not be infecting anyone else in the mean time. Some people would have serious complications, but we would give them the hospital care that we have.
And some people would die.
But at the end of the month, the virus would be gone.
I don’t see anything wrong with my logic, except the incredible suffering it would cause and the political will it would take.
So Should We Despair?
Look, this isn’t great news. But people are coming together and helping how they can.
This enterprising young lady is incentivizing science, which I appreciate:
And Jon Lajoie has even taken the time to salute us nerds, particularly Epidemiologists:
The awesome power of our civilization’s biotechnology industry has been deployed to tackle this singular foe. I have faith that health scientists will finally get our moment to shine, and will pull our species from this morass.
I want to end by sharing an exchange I had with a friend earlier this week. He’s a fellow Epidemiologist in a public health unit, on the front lines of the data side of this crisis. He asked me for something positive to take away from this pandemic, and this is what I wrote to him. Others have found some worth in it, too, so I thought I’d make a permanent record here. Stay positive, my friends! The world is always…. interesting:
“This is a shared human experience like few others in history, a bonding moment. Unlike a war where we are asked to ban together to kill other people, we are bonding together against a common inhuman foe, a virus. This is our chance to be heroic in a way no other generation has had. And look at what we are doing. We are sacrificing our daily freedoms and oodles of wealth to protect our most vulnerable citizens. We should be proud that as a species we have chosen the moral path and not the selfish one.
On a less philosophical note, when this is over (and it will be), our species will have acquired herd immunity to a new class of pathogen. And, more importantly, we will have learned valuable administrative and scientific lessons for guarding against the next big pandemic…. which is coming. But next time we will stop that thing before it leaves its first community.”