It was the alt-history, the policy that didn’t get enacted. No-Covid, zero-Covid or elimination aimed to stamp out community transmission of Covid-19 in a given area, rather than just reduce it to “manageable” levels. Most of the world eschewed it, and it got bad press from the start. Only autocratic regimes could pull it off, one mantra went. Countries like China and ah, New Zealand and, oops, that notorious police state Davis in California. There was something of the self-fulfilling prophecy about this. Many people thought No-Covid was impossible, but the handful of places that embraced it proved them wrong. Now that some of those places are themselves shifting to a reduction or mitigation strategy, countries that opted for mitigation from the beginning are enjoying a “we told you so” moment. But No-Covid’s early champions had to shift in part because other countries let the virus rip. Even if their strategy didn’t remain the optimal one, it bought them time to prepare others. It’s important that we remember that when the next pandemic sidles along. The power of language is terrifying sometimes. We talk about pandemics “erupting” – I’ve done it myself – but sidling seems a more appropriate verb for something that grows quietly in the dark before exploding into the light. The concept of exponential growth is one we have trouble grasping, yet grasping it empowers us. It means that for a time the disease spread is limited and potentially controllable. It means that explosive growth falls off rapidly once it is deprived of fuel. And it means that not everybody has to pursue elimination for it to succeed – as long as a critical mass do. No-Covid was dogged by problems of definition. People confused elimination with eradication, for example. Only one human disease, smallpox, has been eradicated, but plenty have been eliminated. The UK was measles-free until 2017, when partly, due to low vaccine uptake, it lost that status. Elimination is not an unattainable dream, but it does require a concerted effort. In the current pandemic, the word often applied to such efforts was “restrictions”, as if the efforts themselves deprived us of liberty. No. The virus deprives us of liberty; the efforts preserve it. That’s why nobody in Davis is complaining, 18 months into their No-Covid experiment, and why they’re puzzled other US towns haven’t followed suit. Though lockdowns might have been necessary in the beginning, because we had no other shields against the virus, they soon stopped being synonymous with elimination. Cheap mass testing plus isolation of the infected, ventilation, masking, distancing and – importantly – social and financial support for those inconvenienced by these measures, became the preferred tools, used most effectively in combination. The claim that elimination exacerbates inequality is a red herring; it doesn’t, with the right support. A circulating virus certainly does, on the other hand, by preferentially encountering gig workers, keeping kids out of school, and closing mental health clinics. It’s true that some diseases are easier to eliminate than others. Many western countries assumed that Covid would behave like flu, and decided that elimination would be too difficult. China assumed that it would behave like Sars, which it successfully beat 20 years ago. It actually behaves a bit like both, but not exactly like either. Countries tended to get the outcome they aimed for. Last June, a study in The Lancet showed that those that chose elimination over mitigation did a better job of protecting life, the economy and civil liberties – the hat-trick. But no country is an island to a highly transmissible virus – even those that are islands – and the emergence of Delta and Omicron variants of the Sars-CoV-2 virus, combined with the rollout of vaccines that protect against severe disease and death, was bound to change the calculus. Some who favoured elimination previously now think it has outlived its usefulness. New Zealand, for example, has switched to a mitigation strategy. Epidemiologist Michael Baker expects his country’s high levels of vaccination will protect it from a wave of hospitalisations and deaths as Omicron sweeps the country. Hong Kong, which also pursued No-Covid until recently, has tragically not avoided that fate, due to its relatively low vaccination rates. The lesson from Hong Kong is not that elimination doesn’t work, it’s that you need a plan B in case the context changes. Baker and economist Donald Low, who has chronicled Hong Kong’s experience, agree that elimination was the right strategy for the first 18 months of the pandemic. Baker stands by his analysis of December 2020 that, “Elimination might be the preferred strategy for responding to new emerging infectious diseases with pandemic potential and moderate to high severity, particularly while key parameters are being estimated.” What we’re learning about long Covid – or post-Covid-19 condition as the World Health Organization (WHO) now calls it – only strengthens that case, since it’s looking increasingly likely that countries that tolerated high infection rates, including the UK, are facing a sizeable burden of long-term disability. The vaccines do not stop transmission completely, and by abandoning the non-pharmaceutical interventions that do, those countries also increase the likelihood – far from trivial, as scientists highlighted again this month – that a variant more severe than Omicron or its “stealth” subvariant could arise. These emerging facts demonstrate how pointless it is to cost elimination, or any other containment strategy. How do you measure what it has saved you? In speculative fiction terms, what’s the counterfactual? The right way to respond to an unknown disease is to fix a goal and work towards it, adjusting your strategy as you learn. Because there’s another unknown in the equation, human determination, no response should be ruled out initially. As Nelson Mandela said, and the WHO itself likes to quote: “It’s only impossible until it’s done.” Laura Spinney is a science journalist and the author of Pale Rider: The Spanish Flu of 1918 and How it Changed the World