A year ago, when the World Health Organization published a report showing that China had shut down a highly contagious virus in a city of 11 million people, epidemiologist Michael Baker assumed that the international body would advise the rest of the world to follow China’s example. When to his amazement it didn’t, he decided that New Zealand (population 5 million) should go its own way, and started lobbying the government to pursue an elimination strategy.
He found some unexpected allies in New Zealand’s billionaires who, hearing what he was proposing, got on the phone to cabinet ministers too. On 23 March, New Zealand shut down and seven weeks later, its citizens emerged into a virus-free country. Baker, who estimates that the move saved about 8,000 lives, later asked the billionaires why they backed him: “They said, ‘We didn’t get filthy rich by not being good at assessing and managing risk.’ They were in it for the long haul.”
Lately, Baker has been trying to persuade other countries that it’s not too late to switch to an elimination strategy, and that it will be better for them in the long run – even now that vaccines are being rolled out, and even if, as most scientists think, Covid-19 is on its way to becoming endemic. He estimates that about a quarter of the world’s population is now living under elimination strategies, and that number may grow. Europe is deliberating a “no-Covid” policy, while John Nkengasong, who heads the Africa Centres for Disease Control and Prevention, favours it for that continent too – though he knows it’s ambitious.
The rest of the world is pursuing a mitigation and suppression strategy, according to which we will have to live with Covid-19 and therefore we must learn to manage it – aiming for herd immunity by the most painless route possible. The poster child for this approach is Sweden’s chief epidemiologist, Anders Tegnell, who told me last week that elimination was a pipe dream for most of the world because even if a country were able to achieve it once, it would be impossible to prevent reintroductions without maintaining a costly and potentially restrictive surveillance apparatus. If the strategy failed, the country would have to revert to suppression anyway, but the population would have paid a much higher price. He too is in it for the long haul, he says; “sustainability” is his watchword. This is how he justifies the gradual tightening of restrictions in his country, from a very relaxed start.
And so the world is cleaved in two, with each bloc operating according to a different set of assumptions, in a kind of public health rerun of the cold war. One bloc assumes that Covid-19 can be eliminated, the other that it can’t. The latter thinks the former is chasing an impossible utopia. The former thinks the utopia could be achieved if only everyone pulled together.
Epidemiologists build assumptions into their models where there is uncertainty – where they lack data. The assumptions that are made when a new disease emerges are drawn from experience with other diseases. They have to be. Before Covid-19 emerged, most of the world’s pandemic response plans were predicated on flu, because flu has caused most pandemics in history. Flu spreads rapidly through a population, because an infected person can infect others before they develop symptoms, and because the disease has a short serial interval (the time between successive cases) of three days. For these reasons, the consensus is that flu cannot be eliminated; it has to be managed.
The coronaviruses behave differently. Until 2020, epidemiologists might have said that they could be eliminated. That was the experience in 2003 with severe acute respiratory syndrome (Sars), which is caused by a virus closely related to the one that causes Covid-19, and with Middle East respiratory syndrome (Mers), outbreaks of which have been contained locally since 2012. But Covid-19 is a genuine head-scratcher, falling between all stools.
It is more contagious than Sars, Mers and flu, meaning that each infected person infects a higher number of other people, but it spreads more slowly than flu, having a serial interval roughly twice as long. It also has a much longer incubation period, but it’s not clear to what extent presymptomatic – or for that matter, asymptomatic – transmission drives its spread. The proportion of Covid-19 cases that are asymptomatic – once thought to be the vast majority – has been revised down to about 20%.
Deadliness matters too, because it determines how much effort we’re prepared to put into containment. Covid-19 appears to be less deadly than Sars, Mers and the 1918 “Spanish” flu, for now, but more deadly than seasonal flu. The emergence of new variants is changing this picture, as are improvements in patient care. And of course, unlike Sars and Mers, Covid-19 has spread globally. Can we really still rein it in?
Precedents aren’t much help. The WHO has elimination plans in place for a number of diseases including measles, which is far more contagious than Covid-19, but less deadly. Thanks to that plan, the annual death toll of measles – which mainly kills young children – has shrunk by more than 70% since 2000, and now stands at around 140,000. Vaccine hesitancy has contributed to some backsliding lately, but among the countries that retain measles-free status is Sweden. The WHO has no elimination plan for Covid-19, yet some countries have pulled it off, while others nearly have. It also has no elimination plan for seasonal flu, which kills around 650,000 globally each year, yet flu was all but eliminated this year – as a byproduct of efforts to contain Covid-19.
Much uncertainty remains with regard to Covid-19 – not least around the capacity of vaccines to stop its spread. Some things have become painfully clear, however. First, elimination is much easier early on (even Baker admits that fatigue has reduced its chances of success now), and many of those places that fixed their sights on it did so when they still knew almost nothing about the disease. Second, any country that succeeds in eliminating Covid-19 will need to keep its guard up against reintroductions, as is the case with measles, rubella and polio. Third, countries that don’t pursue elimination therefore pose a risk to countries that do. And fourth and most importantly, if governments don’t consider elimination possible, then it isn’t (but if they do, they might end up eliminating some other diseases by accident). In this sense it really is a self-fulfilling prophecy.
Tegnell and Baker agree that we won’t know for some time – perhaps decades – which approach was right, because of the need to assess the social, public health and economic impact of each. That’s true. But the more important point is that much of the world failed to even consider elimination at the outset.
It has often been said that we’re always reacting to the last pandemic, and the most recent one, the H1N1 flu of 2009, was relatively mild. Calls for elimination then would surely have been considered sledgehammer-ish. On average, over the past 500 years, humanity has seen three pandemics a century. Perhaps the next one will be mild, perhaps it won’t. Since we have no way of knowing until it’s upon us, can we at least agree that elimination should be on the table next time around?