Did Sweden Accidentally Blunder into COVID-19 Herd Immunity?
At the beginning of the COVID-19 pandemic, the Swedish government’s chief epidemiologist, Anders Tegnell, denied that his relatively permissive approach to controlling the spread of the coronavirus was aimed at achieving herd immunity.
Unlike most other rich countries—including its Nordic neighbors Denmark, Norway, and Finland—Sweden did not institute a strict lockdown. The government did, in late March, ban public gatherings of more than 50 people, including at theaters and sporting events. But the country decided to let most bars, restaurants, primary schools, and retail shops stay open. Universities and high schools were closed, and people were urged to work from home if possible. Some social distancing rules were adopted, such as limiting the number of customers at a time in shops and providing only table service at bars and restaurants.
Herd immunity is the resistance to the spread of a contagious disease that results if a sufficiently high proportion of a population is immune to the illness. At that point, some people are still susceptible but they are surrounded by immune individuals, who serve as a barrier preventing the microbes from reaching them. Herd immunity can be achieved through either mass infection or mass vaccination. Epidemiologists have converged on an estimate that 60 to 70 percent of people need to either have been vaccinated or infected to reach herd immunity for COVID-19.
While not explicitly adopting disease-induced herd immunity as a policy goal, Swedish public health authorities evidently expected the coronavirus to run quickly through the country’s population while not overwhelming its health care system. If a high enough percentage of Swedes became infected and recovered, then herd immunity would forestall a second wave of the disease.
At the end of April, Tegnell told CNBC: “In major parts of Sweden, around Stockholm, we have reached a plateau (in new cases) and we’re already seeing the effect of herd immunity and in a few weeks’ time we’ll see even more of the effects of that. And in the rest of the country, the situation is stable.” Also in late April, the Swedish Public Health Agency projected that 26 percent of Stockholm’s 2 million residents would have been infected by May 1. “About 30 percent of people in Stockholm have reached a level of immunity,” the Swedish ambassador to the U.S. told NPR. “We could reach herd immunity in the capital as early as next month.”
Yet a May study of blood tests in Stockholm found that only 7.3 percent of the city’s residents had produced antibodies in response to being infected by the coronavirus. This suggested that country was still far from that 60 to 70 percent threshold.
On June 3, as COVID-19 cases in Sweden continued to mount, Tegnell told Swedish Radio, “Should we encounter the same disease, with exactly what we know about it today, I think we would land midway between what Sweden did and what the rest of the world did.” In late April, daily Swedish COVID-19 deaths did peak, but it took until late June for the daily number of cases to begin to decline.
By late July, Tegnell was saying, “The epidemic is now being slowed down, in a way that I think few of us would have believed a week or so ago.” He added, “It really is yet another sign that the Swe
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