COVID-19: Eradication vs Elimination vs Suppression vs Mitigation
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)
Earlier this week, Dr Andrew Morris tweeted, “We need a national debate on COVID strategy,” and tagged many national leaders.
He’s not wrong. Early on in the pandemic, it was assumed by many epidemiologists that we were pursuing the “hammer and dance” made famous by Thomas Pueyo, and that I had written about back in March. The idea back then was that we would endure harsh economic restrictions to buy time to deploy more public health tools and to enact our long term strategy for enduring the pandemic.
But that’s not what happened. Instead, we (in Ontario) suppressed the initial surge (or wave), opened up the economy, and are now suffering a second surge that warrants a renewed set of harsh economic restrictions. Some countries, like Austria, are undertaking another full lockdown.
Clearly, though we “hammered” quite effectively last Spring, we are not “dancing” well. As Dr Isaac Bogoch once tweeted, you can dance only if you know the steps. (I’m paraphrasing.)
As a result, some people are calling for a completely open economy, claiming that “the cure can’t be worse than the disease.” After all, it is intolerable to have to endure multi-week full lockdowns every few months. We would be bankrupt and unable to afford to mount any public health response in a matter of months.
So if this is your source of frustration, what I’m about to say next is very important: No one is advocating for interminable lockdowns or for rolling intermittent lockdowns. No one. And even we Epidemiologists are not calling for continuous brutal economic restrictions until a vaccine arrives.
The intent of the original “hammer”, the first lockdown, was to drive the case numbers down to buy us time to build the public health infrastructure that would allow us to dance. But our leaders failed to do so. Instead, the re-opened businesses and encouraged human interaction far too prematurely, well before we had adequate TTI –testing, tracing, and isolation– infrastructure in place.
Okay. I’m not a fan of pointing fingers with perfect hindsight. Our leaders were under extraordinary pressure to keep constituents happy. The point of today’s post is to enumerate strategies that we can still consider at the national level: strategies that can get us to a state of pseudo-normality and hold us there for as long as it takes for a vaccine to achieve sufficient societal penetration than the pandemic is declared to be over.
Four such strategies come to mind: eradication, elimination, suppression, and mitigation. There is a fifth strategy, that of doing nothing at all, also called the “herd immunity” approach. But I’ve already written about that one.
The weakest approach is mitigation. Mitigation efforts include handwashing, mask wearing, distance learning, travel restrictions and social distancing. Much like the “herd immunity” strategy, mitigation efforts can also include special “focused protection” for particularly vulnerable groups, such as residents of nursing homes.
Mitigation is best used when the disease is already raging through the community and you don’t have enough –or well distributed– testing capacity to identity and quarantine outbreaks in something resembling real time.
Or mitigation is used when the cases are very few, and you have sufficient public health assets in the field such that you’re confident that any new cases can be identified early and snuffed out before they become genuine outbreaks. A good mitigation strategy would include border monitoring to prevent cases from being imported.
Mitigation is pretty much the least we should and could be doing.
Eradication and elimination are different concepts, though some people conflate them. (More on the latter below.) Eradication would be nice. But you really can’t eradicate COVID-19 from the face of the Earth without a viable vaccine, and preferably one that offers neutralizing immunity for life.
Eradicating diseases is very difficult. In general, a few criteria are likely necessary: (1) the natural reservoir of the disease (i.e., the species in which the disease usually lives) should be humans, otherwise it will just retreat to that reservoir and wait you out; (2) natural infection and recovery should confer lifetime immunity, otherwise we’re playing whack-a-mole as the infection moves endlessly from person to person; and (3) you need a well tolerated vaccine that all ages can use and that also offers lifetime immunity.
This all applied to Small Pox. None of it applies to COVID-19…. so far. So unfortunately eradication of COVID-19 is probably off the table for now.
A suppression strategy is essentially a “lockdown”. Business and schools are closed. People are compelled to stay home. This lasts as long as it takes to get the incidence rate down to an acceptable level, whatever that is. The idea is that if you prevent people from interacting, then they can’t spread the disease. After 2 weeks, anyone who had it and didn’t know has probably recovered. After 4-6 weeks, cases will be few indeed.
This is essentially what we (in Canada) did back in the Spring. We drove our case count very low, which allowed our economy to open up in the summer.
The problem, of course, is that when the economy opens up, any lingering cases (or imported cases) find purchase again, and the incidence rate begins to rise again. That’s how you get a “second wave”, which ultimately might require another suppression or lockdown.
The assumption amongst rational people is that suppression buys time to acquire and deploy public health assets, and to unroll a plan to avoid the need for future suppression efforts.
Silly me, expecting our leaders to realize this.
In recent days, many people are talking about the “circuit breaker” strategy, which is a very brief suppression. Instead of suppressing until the cases dwindle to near nothing, you instead suppress for 14-20 days until the incidence rate comes down enough to give your system a chance to catch up.
The advantage of the circuit-breaker is that the population can better tolerate a short term restriction psychologically, and businesses can more easily sustain a couple of weeks of lost revenue.
But of course, as soon as those two weeks are over, the case numbers rise again. Unless something fundamental has changed, there will be a need for another circuit-breaker soon.
New Zealand did it right back in August. They instituted a circuit-break to snuff out the lingering handful of mysterious cases that were jeopardizing their golden elimination utopia.
Elimination differs from eradication in that the disease is not wiped off the face of the Earth. Rather, it is driven out of a country, and the borders are controlled to prevent it from re-entering.
This is done by first getting the case numbers down to zero. Some places are lucky enough to start with very few cases. They snuff those out then enter the elimination regime. For other countries, this is done by first instituting a maximum suppression strategy: close down everything for about two months until cases drop to zero.
Then re-open with limits on social gathering (just in case) and with extreme monitoring of the borders. No one is allowed in without either quarantine, testing, or constant monitoring. The last thing you want is to re-seed your pristine and hard-won COVID-clean country.
Then you sit tight and enjoy your open economy and social intimacy until the vaccine achieves full penetration, allowing you to open up your borders.
New Zealand successfully implemented an elimination strategy. Australia managed it after two hard suppressions. One could argue that Atlantic Canada has done it, too.
6. Suppression & Mitigation
This is what I recommend for Ontario and other provinces. If we look to Northern Canada, Atlantic Canada, and East Asian countries like South Korea and Taiwan, the lessons we see are constant: get case counts very low, then harden your borders and deploy extraordinary amounts of TTI (testing, tracing, isolation) to prevent the cases from overwhelming you.
They still need masks, limits on gatherings, and physical distancing. But all businesses, bars, restaurants, and schools remain open. The economic and psychological tolls are minimal.
This is what the “hammer and dance” scenario was supposed to look like. And frankly, this is what I thought our plan was. I was very much surprised to discover that we did not, in fact, have a plan.
To accomplish this goal, we would institute a hard suppression, likely in the form of a 1-2 month lockdown, to get the incidence rate to single digits per day. In that time, we develop a rigorous backwards contact tracing regime, empowered with strong tracking and isolation powers.
We would also spend the time hardening the borders. Right now, many quarantine-exempt travelers enter Canada (necessarily, as many of them are transporting our needed goods.) We should reserve our rapid testing capacity for these border deployments to ensure that re-seeding events are not re-imported.
Then we re-open with confidence with a mostly fully open economy. We continue like that, with light mitigation, but with no further need for suppression or circuit-breakers for the 9-24 months needed for the vaccine to do its magic.
We need a long term COVID strategy in this country/province. Several options are on the table. Vaccines are coming and they are a very bright light and the end of the dark tunnel. But the tunnel is very long, possibly 1-2 years long. Failure to enact a strategy to allow us to traverse that tunnel in safety and wealth dooms us to rolling cycles of suppressions and circuit-breakers. And no one wants that.