Sweden’s leading epidemiologist says herd immunity a mystery

Photographer: Anders Wiklund / AFP / Getty Images

The man behind Sweden’s coronavirus strategy, best known for the lack of a lockdown, says key questions remain about how immunity works.

Anders Tegnell, a Swedish state epidemiologist, says it is still not clear to what extent transmission rates are reduced when more people have been exposed to the virus.

It’s “very difficult” to understand, he said in an interview on Tuesday, after briefing reporters.

Tegnell’s doubts about immunity follow developments after the summer, with transmission rates having since increased in Sweden and elsewhere in the northern hemisphere. Collective immunity occurs when a sufficient number of people in a community have been infected or vaccinated and are therefore immune. For Covid, the the percentage is estimated to range from 55% to 82%.

Data released by the Swedish National Health Agency in June indicated that around 10% of people in Stockholm – the worst-affected area in Sweden – had developed anti-Covid-19 antibodies. As of last week, there were more than 70,000 confirmed cases and nearly 100,000 positive antibody tests in the Stockholm region, which has a population of 2.4 million.

The balance

“Obviously this slows down transmission, but it has been difficult to understand the magnitude of this effect and how it should be balanced against other factors that speed up transmission,” Tegnell said. This “balance may have been different from what I and many others believed.”

Sweden has made international headlines to avoid a lockdown since the pandemic struck, relying mainly on voluntary measures to achieve social distancing. It’s a strategy that coincides with a death rate multiple of that seen elsewhere in the Nordic region, and the government recently acknowledged that tighter restrictions were needed.

What Bloomberg Economics Says …

“The second wave of Covid-19 started later in Sweden and the number of new cases continues to rise, according to data released on December 1. In contrast, the infection rate appears to be declining in other parts of Europe. A continued increase in new hospital admissions and an increase in mortality from Covid-19 also shows that the pandemic has tightened its grip in Sweden.

– Johanna Jeansson, research economist

For the full grade, click here

Although Sweden has never targeted collective immunity as a stated strategy, officials have made it clear that they expect some form resistance to integrate the population that would limit the spread of Covid-19.

Part of the difficulty in predicting immunity levels, Tegnell said, is false assumptions that many more people have been infected than official data shows.

“What we have tried to achieve from the start is to minimize transmission with measures that have had the least possible adverse effect on public health,” Tegnell said. “And that’s what we’re still doing.”

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