Danish COVID tally could be twice as high as registered, blood donor data suggests

People sit at Kaffesalonen (The Coffee Saloon) as coronavirus disease (COVID-19) restrictions ease, in central Copenhagen, Denmark, April 21, 2021. REUTERS/Tim Barsoe/

COPENHAGEN, Feb 3 (Reuters) - The number of adult Danes infected with COVID-19 may be double the official tally, Danish scientists said on Thursday, after releasing data suggesting one third of the adult population has been infected in the past three months.

By screening blood donations for certain antibodies, Danish scientists say they have come closer to determining how many people are actually infected, following the emergence of the more infectious Omicron variant.

The preliminary research, conducted by the Nordic country's top infectious disease authority, Statens Serum Institut (SSI), was based on analysis of 4,722 blood donations collected in mid-January.

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The blood was analysed to see whether it contained antibodies against the virus' so-called nucleocapsid protein.

This type of antibody is only created when the body encounters the real coronavirus. It would not figure in blood samples from persons, who had never been infected, even though they have developed antibodies from vaccines.

"The results indicate that... the proportion of infected people who have not tested positive makes up between a third and a half of all infections," SSI director Henrik Ullum said in a statement.

That means that for every 100 coronavirus infections registered, another 100 infections could go unreported.

According to official numbers, 1.2 million infections have been registered since Nov 1, around a fifth of the population. But that number includes children's infections and reinfections.

SSI's preliminary findings, which it says are subject to some uncertainty, could help authorities better predict the trajectory of the epidemic and shed light on population immunity, it said.

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Reporting by Nikolaj Skydsgaard Editing by Alexandra Hudson

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