Coronavirus: Sweden--Herd Immunity vs Herd Mentality
Why are we talking about Sweden?
Well, I love Ingmar Bergman’s movies (and my favorite, The Seventh Seal, is set at the time of the plague—the real one), but that’s not the reason. We need to talk about Sweden because in the coronavirus crisis it has chosen the road not taken—it has not shut down its economy, and has relied instead on voluntary social distancing measures and moderate restrictions. In so doing, it put itself at the center of a heated controversy.
What has Sweden done?
Urged citizens to follow basic social distancing and hygiene guidelines, especially elderly people. Recommended that people work from home if they can, and that colleges and universities switch to online learning. (You can check the official Public Health Agency’s guidelines here)
Bolstered capacity in its health care system, including setting up emergency health care facilities around the country.
Kept open restaurants, bars, gyms and shops (restaurants and bars have to avoid overcrowding).
Kept its borders open.
Is Sweden’s approach so different?
Yes, in some very important ways. The goal is still to “flatten the curve”, to slow the spread of contagion to prevent the health care system from being overwhelmed—as Anders Tegnell, the Public Health Agency epidemiologist who guided the response strategy, notes in this interview. But unlike many other countries, Sweden has done so through voluntary and moderate restrictions, and kept most businesses open. This is partly because Sweden’s experts do not believe there is any scientific evidence that locking down cities and closing borders helps.
Sweden’s epidemiologists and policymakers have also been more focused on the human and social costs of lock-down measures. Tegnell notes “it is instrumental for psychiatric and physical health that the younger generation stays active” and that schools stay open.
Is Sweden aiming for “herd immunity”?
Yes. “Herd immunity” has become another four-letter-word expression; mention it, and people treat you like a murderer. The irony is, epidemiologists agree that herd immunity is the only viable end-game—see this Q&A from the Johns Hopkins Bloomberg School of Public Health. The disagreement is on how to reach it.
Herd immunity is obtained when a large enough share of the population has become immune to the virus, so that contagion slows and eventually dies out. You can reach herd immunity in two ways: with a vaccine, or by having enough people be exposed to the virus and develop an immune response.
Most experts believe that developing and producing a vaccine will take at least 18 months. The crucial choice, therefore, lies in weighing the costs of allowing most people to be exposed to the virus against the costs of keeping the country locked down for up to 18 months.
Many Western countries decided early on that the costs of allowing the virus to spread would be overwhelming. Models like that of Imperial College London and the Institute for Health Metrics and Evaluation at the University of Washington predicted over 2 million deaths in the US and half a million in the UK. These frightening projections received wide media coverage. By comparison, there was little public discussion of what the economic and health costs of a long shutdown would be.
Leading Swedish epidemiologists came to a different conclusion: that the virus is less dangerous than implied by the models, and that a long shutdown would be untenable. Dr. Johan Giesecke, advisor to the WHO and Sweden’s former state epidemiologist, states in this interview that he believes the Imperial College model’s projections were unreliable and excessively pessimistic; and that in a democracy a shutdown cannot be extended for as long as it takes to develop a vaccine.
Sweden therefore decided that the best strategy is to allow the population to gradually become exposed and develop immunity, but with two precautions: (i) seek to isolate and protect the elderly; (ii) implement moderate social distancing to prevent hospitals from being overwhelmed.
How is Sweden’s strategy working compared to other countries?
Sweden’s approach has attracted enormous criticism. Hans Bergstrom, professor of political science and former newspaper editor, argues in this article that Sweden’s response has been misguided and caused the country to suffer “one of the world’s highest Covid-19 death rates”; his article links to a similarly harsh criticism leveled by 22 of Sweden’s medical experts.
Is Covid-19 killing more people in Sweden? Bergstrom’s article displays a table with deaths per million people, showing Sweden as having a much higher mortality rate than Denmark, Norway, Finland and Germany. Fair enough. But here’s a chart that includes a few more countries: Sweden’s mortality rate is much lower than those of Belgium, Spain, Italy, France, the UK and the Netherlands—countries that locked down their economies.
The chart above uses April 17 data, same as in the Bergstrom article. The latest data (24 April) give a very similar picture (I am using the dataset from Our World in Data):
Does Sweden have more infected cases than its peers? Not according to confirmed cases, which per million people are a bit higher than Denmark and Norway, but a lot lower than the US and many others.
Remember however that the number of recorded cases depends on how many tests you perform (as I stressed in my first blog on the topic). Sweden has tested a smaller fraction of its population than many of its peers – though on a par with France and larger than the UK. Remember also that Sweden is explicitly targeting herd immunity, so a higher incidence of cases would in fact be in line with its strategy--provided mortality remains contained.
What about the trend in mortality? The next chart shows the 7-day moving average of daily Covid19 deaths. Sweden is highlighted in orange. This is a log chart, so if something is going up in sort of straight line it is increasing exponentially. Sweden’s average has trended up between April 15 and April 22, then edged down in the following two days (France and the UK have flattened, and Italy and Spain have declined). This needs to be watched, but based on the latest data it does not look like Sweden’s situation is getting rapidly worse.
Moreover, Sweden’s health care system has not been stretched: there has been no shortage of medical equipment, and emergency tent facilities have remained unused.
What should we learn from Sweden?
Sweden has aimed to slow contagion and allow the population to build immunity without crippling the economy or drastically curtailing individual freedoms. If it succeeds, people in the US, Italy, the UK and other countries will ask: why didn’t we do the same? If Sweden succeeds, it will show that imposing extreme social distancing and locking down the economy was not the only way to go—that a less extreme and more targeted strategy was a better alternative. That, in my view, is why so many people do not want Sweden to succeed, and explains the relentless harsh criticism that Sweden is receiving. By targeting herd immunity Sweden has refused to follow the herd.
But we should be looking at Sweden’s experience in a very different way. As policymakers in the US and elsewhere consider reopening their economies, they worry of what will happen to contagion; they will need to decide how to react if the virus reappears after the summer. Sweden’s example might offer a guide as to how to safely restart economic activity and almost-normal life—and it might offer reassurance that the virus is not as dangerous as the models have been telling us.
We should want Sweden to succeed, not fail—for our own sake.