Sweden and Denmark are both Nordic countries speaking similar languages, sharing a lot of culture and a lot of common history. But they followed very different approaches to managing the Covid-19 pandemic. Denmark was among the first in Europe to shut down schools, restaurants and other businesses like beauty salons. Sweden, in contrast, allowed businesses to stay open and street travel to continue unimpeded. These two countries, thus, offer us a natural experiment to investigate the effectiveness of lockdown in controlling Coronavirus. This question is quite important, as lockdown is hugely disruptive both socially and economically.
Currently it looks bad for Sweden. It’s deaths per 100,000 population due to Coronavirus are about three times as high as in Denmark. Here’s a good (although week-old) summary of evidence: Sweden says its coronavirus approach has worked. The numbers suggest a different story.
Of course, Sweden and Denmark, despite their strong similarities, differ in some ways. This is a problem with natural experiments. For example, Denmark’s population density is much higher than in Sweden. But that should make Denmark’s epidemic harder to control, so this consideration only strengthens the conclusion that a lack of lockdown hurt Sweden. In Norway and Finland, which, like Denmark, closed themselves down, but have population densities comparable to Sweden, death rates have been even lower than in Denmark, making the contrast with Sweden even more striking.
Still, a comparison of death rates, while useful, doesn’t really get at the most important question: how differently did Sweden and Denmark manage to depress the rate of spread of the epidemic? After all, one thing we learned recently is that death rates per 100,000 differ dramatically among countries, much more than expected, and we don’t know why. So a direct comparison of disease transmission rates and the resulting exponential growth rate of the epidemic is in order.
A month ago, as part of the CSH-Vienna initiative on Covid-19, I developed a model-based approach to analyzing epidemic trajectories (see How Effective Are Public Health Measures in Stopping Covid-19?). So let’s see what it tells us about Sweden versus Denmark.
Let’s first look at Denmark. Most of the charts below are self-explanatory. In (a) through (f) data are indicated by points, and model trajectory is shown by the curves. The interesting parts are in the bottom tier. Thus, beta(t) in panel (g) shows how the disease transmission rate responded to the lockdown. It started quite high, around 0.3, which means that the number of infected grew by 30% every day. After March 15 it dropped to 0.1, and the gradually declined to half that, although with fluctuations. In (h) delta(t) is the death rate about which I will talk a little later. The most interesting is (i) r(t). This is the exponential rate of increase. The goal is to bring it below 0 at which point the epidemic starts to subside. Denmark succeeded in this by April 15. This is good news.
Now let’s look at Sweden:
Swedish dynamics are surprisingly similar to those in Denmark. There was also a rapid decline in the transmission rate, beta(t), by March 15, but not as deep as in Denmark. After that beta continued to decline, but again ,more slowly than In Denmark. As a result, the exponential rate of disease growth approached the zero-level veeery slowly and has just touched it yesterday (we don’t yet know whether this will be sustained).
So the verdict seems clear, although perhaps not as clearcut as might be expected. The approach of Denmark clearly worked, rapidly bringing an end to the epidemic there. But Sweden didn’t do as poorly as I expected. Somehow, despite a lack of lockdown, they are depressing the transmission rate down.
Let’s now look at death rates. Note that these are not death rates per 100,00 which conflate two processes: what proportion of population is infected and what proportion of infected dies. This is a look at just the second part.
Surprisingly, we find that for most of April, Coronavirus patients in Sweden had nearly twice as great probability of dying than in Denmark. I’ll offer a possible explanation below, but it is clear that it made a rather large contribution to the difference between death rates per 100,000 in Sweden and Denmark.
I started this analysis expecting to demonstrate clear support for the wisdom of lockdown. Make no mistake, I continue to be a strong proponent for comprehensive shutdown as the best currently available method of controlling the Coronavirus pandemic. In personal life my preference, definitely, is to endure sharp pain now to solve the problem in the long term. In line with this philosophy, I think we should drive Coronavirus to extinction.
But in science one needs to set one’s personal preferences aside. It turns out that the comparison between Sweden and Denmark has some hidden complexities that we shouldn’t ignore. Let’s rerturn to the difference in delta, the death rate. If it’s real, then it weakens the case for comprehensive lockdown. On the other hand, Sweden has tested a much lower proportion of population for the virus. What if the elevated death rate there is a result of a larger number of unknown infecteds? These are the kinds of complexities that need to be resolved.