COVID-19: Can We Eradicate the Virus?
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)
Now that we have several vaccines against COVID-19, I keep getting the same four questions: (a) Which one should I get? (b) Are they safe? (c) Will we have to do this every year? And (d) Does this mean we can get rid of COVID-19 once and for all?
Today I’m only going to try to answer the last question. Both the Pfizer and Moderna jabs are thought to be 94-95% effective. That’s an extraordinarily high number, especially given that the seasonal flu jab usually is about 40% effective, and we would have been very content with a COVID vaccine of 50-60% effectiveness.
The Astra Zeneca and Johnson & Johnson vaccines also have high efficacy scores, as well. But right now we have more experience with the mRNA vaccines in Canada.
(If you’re curious, I’ve attempted to explain much of the vaccine science in an earlier post, and I recruited virologist Dr Erling Rud to answer vaccine questions in an earlier podcast.)
This high effectiveness has got some people asking…. well, can we now wipe this disease off the face of the Earth? So today I want to briefly talk about disease eradication and why it’s so hard.
What Are Our Options for Managing COVID-19?
First off, when it comes to dealing with viral epidemics, we really only have three options:
(1) Control: When we use local mitigation tools, like mask-wearing, and regular screening and testing, to keep local incidence rates of the disease to manageable levels. It’s kind of what we were hoping to achieve throughout this past year, but mostly failed to do so.
Imagine a scenario in which vaccines were not available, and we’d have to live with COVID-19 as a simmering disease for the foreseeable future. It would not be untenable, just a little inconvenient and expensive.
(2) Elimination: When we drive all instances of the disease from within our borders. “Covid-Zero” was a campaign designed to achieve just this. Nations like New Zealand famously achieved this state by acting early, acting decisively, and by hardening their borders against imported new infection.
In vaccines were not available, the lure of a national Elimination strategy would become increasingly enticing.
(3) Eradication: This is what we want, the systematic removal of all traces of the SARS-Cov2 virus from any population anywhere on Earth. We have achieved this twice in human history, with the viruses for Rinderpest and Small Pox. We continue to try to eradicate disease like polio and guinea worm, but it’s proving to be difficult.
Some people like to distinguish between “disease eradication” and “infection eradication.” With the former, we can still have asymptomatic infections that do not lead to actual disease, or presence of the pathogen in the environment that does not lead to measurable disease. A good example of this is neonatal tetanus.
The bacterium that causes tetanus cannot be wiped out because its spores are widespread in soil. But the disease that the the bacterium causes can be universally prevented with vaccination.
(4) There is a fourth possibility: Extinction. Small Pox is eradicated but still exists in research labs in places around the world. If those samples were destroyed, then the disease would be truly extinct.
I recently saw Dr Fauci comment on TV that he believes our response to COVID will be somewhere between “Control” and “Elimination”, but that “Eradication” is unlikely. Let’s get into why that is the case.
Criteria for Eradication
Small Pox was eradicated because of a global effort to do so. But there were some truths that allowed that great feat to take place. By comparing the characteristics of Small Pox with COVID, we can see how the latter has a much harder path to eradication:
(1) Reservoir: the natural reservoir of Small Pox is human beings. This word “reservoir” refers to the population of hosts in which a pathogen usually lives. If the reservoir is a single species, then that makes our job much easier. We can locate pretty much all the human beings on Earth. We can’t locate all the rats, for example.
Several diseases that we’ve managed to control keep pinging back into the human population because they hide silently among non-human animals. Yellow fever and chikungunya come to mind.
We know that the SARS-CoV2 virus is a zoonotic one, meaning that it arose in another species…. a bat maybe, or a pangolin. We also know that it can infect other higher primates, like gorillas, and even some dogs and cats. Therefore, even if it were eliminated among humans, it could retreat to a non-human species and bide its time until humans were susceptible again. This is not cool.
(2) Detection: Nearly all persons infected with smallpox had an obvious, characteristic rash. This made identifying infected people comparably very easy. As we all know, COVID is frequently transmitted asymptomatically. This means that without extensive screening programs, we will never identify the vast majority of carriers.
(3) Infectious Period: Small Pox victims were infectious for a relatively short period of time, but did have an asymptomatic yet infectious incubation period, not unlike what we see with COVID. In this sense, we have an advantage with COVID. Its short infectious period means that with sufficient resources and effort, containment is possible.
(4) Natural immunity: If someone were infected with Small Pox and lived to tell the tale, they were then immune for life. That’s useful. It meant that we didn’t have to re-vaccinated people who had already suffered through the disease. It also meant that the “susceptible population” fell off as infection progressed. Whereas, with COVID, we know that reinfection is possible, increasing in likelihood after about 90 days.
We have much to study, still, about the extent of immunity offered by natural infection and recovery. But it is definitely not absolute.
(5) The vaccine: Small Pox benefited from a safe, highly efficacious (~95%) vaccine that was inexpensive, effective in all age groups (even newborns) and stable in all environments, even hot tropical ones. The vaccine also conferred lifelong immunity. The COVID-19 vaccines are new, so we’re still learning about them. But so far they’re typically only available for adults, the most efficacious ones (the mRNA ones) have to be kept in deep freeze, and longevity of their immunogenic effects is still largely unknown, though most experts agree that they are unlikely to confer lifelong immunity.
Can COVID be Eradicated?
As you can see from the list above, the odds are stacked against the eradication of COVID-19. While our highly efficacious vaccines offer that tantalizing possibility, they do not (as far as we know) offer lifelong immunity, nor has it been shown (yet) that they are efficacious in children, nor is their deployment to the far niches of the world a simple task.
The existence of non-human animal reservoirs almost closes the door on eradication outright. But at least COVID hasn’t moved into insects (as far as we know), but only mammals. We could, in theory, with an overwhelming amount of effort and resources, contain those non-human cases. But I’m skeptical.
Another factor is the rise of mutations that might change: the disease’s transmissibility and lethality, the species in can affect, and whether our vaccines are effective.
Nature has a good graphic for understanding how these unknowns affect our prediction of the likely path of the pandemic:
Conclusion:
COVID-19 is unlikely to be eradicated. But we have a fair chance of eliminating it from inside our borders. And we have a very good chance of controlling it so well that it appears to have been eliminated. We have done this with many other diseases through the layered application of vaccination, pest control, and population screening. It’s why most of us go about our day without mortal fear of age-old killers like measles, polio, and dysentery. COVID-19 will enter the catalogue of such diseases managed in real-time by our unrecognized public health heroes.
We’re almost there.
