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What is ‘hybrid immunity,’ which Denmark is touting as the reason it lifted COVID curbs?

February 15, 2022, 4:17 PM UTC

Denmark’s hands-off strategy on the coronavirus might be paying off. 

On Tuesday, it registered a decline in the contagion rate for the first time in over a month, indicating that the Nordic country is getting close to so-called hybrid immunity—a combination of vaccinations and infections.

After becoming one of the first European countries to abandon pandemic restrictions, cases surged to levels far higher than more cautious neighbors like Germany. That raised questions about the approach, including from the likes of Nobel laureate economist Paul Krugman.

Two weeks after Denmark declared that COVID-19 was no longer a threat to society, the so-called reproduction rate fell to 0.9 on Tuesday, meaning the outbreak is shrinking. It was the first time the R-rate was below 1 since Jan. 4, when health authorities said the data was skewed due to the Christmas holiday.

The decline is backed by sewage samples showing lower virus levels, Tyra Grove Krause, a director at Denmark’s institute for infectious disease, said in an emailed reply to Bloomberg questions.

“We expect the drop is due to hybrid immunity, caused by high vaccination rates and immunity after an infection, because the decline is largest in the areas where the infection rates were previously the highest,” she said.

What our analysts say on hybrid immunity:

Third COVID-19 vaccine shots, and hybrid immunity (a vaccination plus an infection)—which Omicron’s transmissibility renders quasi inevitable—may be the sole way of easing the global health burden, aside from zero-COVID strategies. 

-—Sam Fazeli, BI analyst. Read the research here.

Denmark has been a pioneer in COVID strategy. It was among the first to impose lockdowns in 2020 but has since focused on softer curbs—although not as light as in neighboring Sweden. The validation of its current approach could encourage more countries to follow suit.  

The country stuck to its line even as the virus spread faster this year as the BA.2 sub-variant of Omicron—which is significantly more transmissible—became the dominant strain. 

While the change in the trend is welcome, the current infection level is still 10 times higher than in November. That’s not really a concern though, says Krause. Given the milder symptoms caused by Omicron, the most important data to monitor is hospitalizations at intensive-care units, she said. Those numbers have also declined.

High vaccination rates have helped shield Danes and kept hospitals from overflowing, despite the rampant spread of the virus. About 84% of population has received at least one vaccination shot and nearly two-thirds have received three. Meanwhile, the country of 5.8 million people has registered 2.3 million cases, including reinfections. 

Even holdouts are now rolling back restrictions, Germany on Wednesday will consider a plan that would see most pandemic restrictions lifted by March 20, even though it just reported an all-time high in cases on Saturday. 

Denmark has been able to avoid curbs because of one of the world’s most aggressive testing strategies, Krause said.

“In addition, the population has a high degree of trust in recommendations from the health authorities and have supported the vaccination drive,” she said.

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