Forty years later, we have a new virus to contend with. Although it doesn’t have a truly terrifying 30% mortality rate like smallpox, the coronavirus SARS-CoV-2 is vicious enough to have killed 1.5 million people in less than a year, and has shut down economies worldwide. A major reason for those shutdowns, of course, was that we didn’t have a vaccine: there was no option but to attempt to stop people from spreading it by keeping them apart. But now we do have vaccines – several of them, and they’re accompanied by a much better understanding of how SARS-CoV-2 works. Imagine how satisfying it would be — after a 2020 filled with disease, death, lockdown, loneliness, bankruptcy and general misery — if we could eradicate this virus too. 

This might seem like we’re jumping the gun. After all, as we write this, nobody outside of clinical trials has actually been vaccinated against the coronavirus. But the most sophisticated vaccination programme in world history will begin within the next few days. How likely is it that we can get rid of this thing altogether?

First things first. Is eradicating our novel coronavirus even possible? This wouldn’t be the case for, say, the virus that causes influenza — mainly because there isn’t just one major flu strain, but many dozens, each of which is constantly and rapidly evolving. We have to come up with a new flu vaccine every year, and eradicating all the different strains just isn’t viable with our current technology. The Covid-19 coronavirus, on the other hand, evolves far more slowly, opening up the possibility that we could tamp it down with the right combination of vaccines and other measures.

Evolution is actually one of the prime reasons we should want to try to wipe out this new virus. Even though it might do so slowly, it’s still possible that it might evolve a new strain — one that’s deadlier and which the vaccines we’ve just developed don’t counter. This isn’t a far-fetched idea: the closely-related coronavirus that causes SARS has a fatality rate somewhere around 15%, and the even scarier one that causes MERS is worse than smallpox, killing around 34% of cases.

But even setting aside evolution, eradicating SARS-CoV-2 would have clear benefits. It would obviously reduce the suffering caused by the disease, and lessen the likelihood of flare-ups in specific parts of the world — most likely poorer countries where vaccines are harder to come by. It would also save us money in the long run. If the virus is always with us, we’ll always have to vaccinate against it: even if immunity from a vaccine is long term, it won’t be forever, and as populations grow, there will be more of us to vaccinate. Every penny not spent on regularly vaccinating people against COVID-19, after it’s no longer an issue, could be spent on improving health in other ways.

So there’s a clear rationale for eradicating the disease, and it might even be possible in theory. What about in practice?

To date, only two infectious diseases have ever been eradicated — the aforementioned smallpox, and also rinderpest, a particularly nasty cattle virus that can have a near-100% fatality rate, which was wiped out in 2011. That should tell us that removing a disease from circulation is an extraordinarily difficult task.

Smallpox had been endemic in Asia for perhaps 2,000 years. By the 18th century, it killed around 400,000 people in Europe annually. Wars, conquests and the slave trade introduced the disease into the Americas, South Africa and Australia, and records suggest that it destroyed entire tribes in what are now South Africa, Kenya and the Democratic Republic of the Congo in the 19th century, and killed huge swathes of people living in urban settlements.

In the years before a vaccine, authorities quarantined ships to prevent the disease from being introduced into disease-free ports; when that became unviable, some communities practised variolation — a risky procedure where people were deliberately exposed to weakened forms of the virus to protect them from the fatal strain. However, Edward Jenner’s invention of the smallpox vaccine in 1796 — the first ever vaccine, in fact — was a game-changer, leading to the first real reductions in the incidence of the disease. As time passed, techniques used to manufacture, store and administer vaccines improved tremendously, and states initiated vaccination programmes to inoculate their citizens from the deadly disease.

Although smallpox was eliminated in some regions in the early 20th century, the prospect that it could be eradicated across the world was met with widespread scepticism, and was not even considered a serious possibility until 1958, when the WHO resolved to guide a worldwide campaign. The operation was a decentralised undertaking, and it took decades to secure funding and political support for eradication everywhere — for many years, it was simply not seen as a priority, or even an interest, to many governments or community leaders. Where money was available, the strategy began with mass vaccination and shifted towards tracing and containment as cases declined. Eradication was finally achieved in 1980, 184 years after the vaccine was first invented.

The problems that beset the smallpox eradication programme — poverty and a lack of funding — are also major reasons that other diseases haven’t yet been beaten. For example, the Rockefeller Foundation’s early 20th-Century effort to wipe out hookworm, a parasite that can create a drag on children’s development, was very nearly successful, but it didn’t quite penetrate far enough into the world’s least developed places, where poor sanitation and infrastructure help the worms spread.

Hookworm has even come back in extremely deprived parts of the US, where it was thought to be eliminated. A similar story can be told for yaws, a bacterial disease that causes ulcers and physical deformities, and which keeps returning in the very poorest parts of the world.

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A more optimistic story concerning a parasitic infection is that of Guinea worm disease, where a worm grows in the host’s flesh and creates an extremely painful wound, stopping them from walking or working, and making them vulnerable to further bacterial infection. Since there’s no vaccine for a non-viral disease like this, education is the main way to prevent it: The Carter Centre, established by the former US president, has been showing people good ways to clean and filter drinking water, among other strategies, and has been the main cause of global disease cases declining from around a million in 1989 to double figures in recent years. We’re many years behind our elimination target, however: the disease remains in very poor countries in Africa, such as Chad and South Sudan.

Poverty has also frustrated attempts to eradicate polio, which infected millions across the 20th century, resulting in death, paralysis, skeletal deformity or confinement to a coffin-like iron lung for weeks, months or years. The plan was to eradicate the three different kinds of wild poliovirus by the year 2000, but it proved trickier than expected. Nevertheless, the virus’s days are numbered: India was declared polio-free in 2014, then Nigeria as recently as August 2020. Presently there remains only one wild type of poliovirus, and it remains endemic only to the neighbouring countries of Afghanistan and Pakistan. 

Other eradication attempts have run aground for other reasons. The effort begun in the late 1940s to rid the world of malaria, for instance, was a failure due not only to ballooning budgets, but to our old friend evolution: mosquitoes evolved resistance to DDT, the pesticide that had previously, and successfully, been used to exterminate them. Now, eradication is back on the table: in September 2019, a special commission put together by the medical journal The Lancet projected that with the right policies, we could still eradicate malaria within a generation.

So whereas there are reasons for hope about freeing the world from polio, Guinea worm and maybe even malaria, we haven’t finished the job on any of them yet, and we’re in some cases decades behind schedule. These are all reasons to temper our expectations about eradicating SARS-CoV-2. And we’re about to see another.

In a word, the problem is animals. The fact that other mammals can be infected with a virus makes it vastly more difficult to stamp out a disease, as the persistance of rabies shows. Vaccinating animals — especially wild and stray ones — is understandably far more difficult than vaccinating people. Indeed, the reason we can’t technically say that we eradicated the SARS or MERS viruses, despite their spread through humans being completely halted, is that they still circulate among non-human animals — and since there’s no vaccine for either disease, it’s quite possible that they’ll reappear in future. 

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We already know that the novel coronavirus can infect bats, cats (including lions and tigers), dogs, monkeys, ferrets, hamsters and shrews, among other species. In recent weeks, Denmark had to cull 17 million mink after outbreaks in humans were traced to infections among the animals on farms where they were bred for their fur (and in a rather grim sequel, thousands of them had to be dug back up again). 

Of course, the origin of the virus is bats — they’re one of the major non-human carriers (the technical term is “reservoirs”) of SARS coronaviruses. Virologists have for years made predictions that bats would be the source of new disease outbreaks: they carry a wide variety of coronaviruses, they’re widely dispersed around the world, often live near humans and can migrate easily, and the viruses they carry are likely to cause disease and jump to humans. That suggests that vaccinating just bats — and the particular species that carry human-infectious viruses, rather than all the other potentially-infected animals — would get us quite far.

When authorities began to control the spread of rinderpest, they did so by isolating infected farm animals and restricting their movement, culling them and disinfecting their habitats, all before a vaccine was developed. With COVID-19, we have a head start given we already have a vaccine — and it would be relatively straightforward to develop a bat-version. We could put oral vaccines in bait — a common strategy for controlling disease in wild animals.

There are also other ways to prevent SARS coronaviruses from jumping to humans once again. Most countries, for example, already mandate vaccinations and travel quarantines for animals entering the country. And we could focus on improving hygiene standards for handling wild animals — particularly of the flying mammal variety. In the future, it could even be the case that new vaccines will protect us against multiple strains of SARS coronaviruses at the same time.

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There are several other factors that affect whether a disease is eradicable. One is how easy it is to detect: if you can precisely pinpoint who has the virus, you can get them quarantined as soon as possible. That’s not really a check in favour of the eradication of Covid-19, since its symptoms — particularly the cough and the fever — can easily be confused with those of other viruses, such as the flu. On the other hand, better diagnostic tests are being developed all the time, and we might soon end up in a situation where super-rapid, super-accurate, super-cheap tests can help us rapidly isolate people carrying the virus.

Another factor is how easy the disease is to prevent. Although the initial evidence suggests that at least two of the vaccines for Covid-19 developed so far are extremely effective at preventing symptoms, we don’t really know yet whether they also prevent transmission of the virus, and indeed whether they prevent infection itself. Luckily, there are good scientific reasons to think this latter will be the case. We’re also getting better at preventing spread through non-pharmaceutical means: not just lockdowns, but less invasive interventions like masks, ventilation of rooms, social distancing, and contact tracing, all of which improve as we learn more about the mechanics of how the virus spreads. 

This is another area where technical advances will likely help us in future. At the moment, our vaccines are (literally) a shot in the arm. Nasal vaccines, which vaccinate the upper as well as the lower respiratory tract, are more likely to stop transmission as well as symptoms in the vaccinated person, and could well be developed in the months and years to come (we’ll also need an oral vaccine for those wild animals).

Ventilation technology will also probably improve, allowing us to spend more anxiety-free time indoors (as in so many things, hospitals in East Asia learned this lesson well after the original SARS outbreak in 2003). Even simpler technologies, like new types of masks that are more tolerable to wear and thus more likely to be effectively used, could help slow the spread.

Finally, is it possible to eliminate the virus in particular regions of the world? If so, it increases the plausibility of doing it on a wider scale. For COVID-19, the answer seems to be a cautious yes: there are regions that, right from the start of the pandemic, have had extremely low transmission thanks to effective tracing, quarantine and other policies.

For example, from the perspective of the UK, with our population of 67 million and 80,000 deaths, it seems unbelievable that Vietnam (population 96 million) has had a mere 1,358 confirmed cases and 35 deaths. That’s not full elimination by any means, but it — along with the extremely impressive performance of other Asian and Australasian countries, even without a vaccine — goes to show that good policy really can drive the virus down to near-negligible levels.

And that’s probably the best we can hope for: getting things to the point where, like SARS and MERS, the virus is effectively gone, even if not fully eradicated. The fact we have a vaccine means we’re already in a better position than for those two other coronaviruses; but that the virus is so contagious, and has already spread to every corner of the globe, makes things more difficult. The good thing is that the strategies mentioned above will all reduce the burden of disease, with all its associated costs to life and to our economies, even if they fail to completely extirpate the virus. For that reason, aiming for eradication is the smartest strategy.

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Even if we can’t win the peoples of the world their freedom from SARS-CoV-2, all our technological advances might render it far less risky to be infected. The model here is HIV: even though there’s no vaccine or cure, with the right drugs the virus is no longer a death sentence. We’ve already seen the novel coronavirus become less deadly as our medical treatments have improved; better steroids, anti-virals, and perhaps even synthetic antibodies could reduce the fatality rate even further.

The Covid-19 pandemic has given us plenty of reason to despair, but all the scientific progress we’ve made in a few short months gives us a lot to feel optimistic about, too. The urgency of the pandemic has meant that we’ve accelerated reviews by regulatory agencies, poured vast funding into research and development, and developed not one but multiple effective vaccines at an unprecedented speed. 

When all the world’s attention is focused in the right way, we’ve seen that the most vexing problems can suddenly become solvable. For millennia, humans had been unable to exterminate any infectious disease. And yet just in the last century, our technology and ambition allowed us to declare victory against two of them, and set us on track to defeat several more. Once the first wave of mass Covid vaccination begins, we shouldn’t rest on our laurels. We should do our very best to free ourselves of this virus forever.