People who have survived cancer as children are at higher risk of developing severe COVID-19, even decades after their diagnosis. This is shown by a new study from Karolinska Institutet published in the journal The Lancet Regional Health – Europe.

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Source: Stefan Zimmerman

Javier Louro

Thanks to medical advances, more and more children are surviving cancer. However, even long after treatment has ended, health risks may remain. In a new registry study, researchers investigated how adult childhood cancer survivors in Sweden and Denmark were affected by the COVID-19 pandemic.

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The study included more than 13,000 people who had been diagnosed with cancer before the age of 20 and who were at least 20 years old when the pandemic began. They were compared with both siblings and randomly selected individuals from the population of the same gender and year of birth.

The results show that childhood cancer survivors had a lower risk of contracting COVID-19, but were 58 per cent more likely to develop severe disease if they did become infected. Severe COVID-19 was defined as the patient receiving hospital care, intensive care or death related to the infection.

More serious consequences

”It is important to understand that even though these individuals were not infected more often, the consequences were more serious when they did become ill,” says Javier Louro, postdoctoral researcher at the Institute of Environmental Medicine at Karolinska Institutet and first author of the study.

The differences in risk were particularly clear during periods of high transmission, such as when new virus variants such as Alpha and Omicron spread rapidly. In Sweden, where pandemic management was based more on recommendations than restrictions, the increase in risk was greater than in Denmark, which introduced early and strict measures.

Risk group

”Our results suggest that childhood cancer survivors should be considered a risk group in future pandemics or other health crises. This could involve prioritising them for vaccination or offering special protection during periods of high transmission,” says Javier Louro.

The study was conducted in collaboration with the Danish Cancer Institute. The study was funded by the Swedish Childhood Cancer Fund and the Swedish Research Council, among other sources. Se the article for full information about funding and any conflicts of interest.

Publication: “COVID-19 infection and severity among childhood cancer survivors in Denmark and Sweden: a register-based cohort study”, Javier Louro, Christina-Evmorfia Kampitsi, Hanna Mogensen, Friederike Erdmann, Karin Modig, Anna Nilsson, Mats Heyman, Henrik Hasle, Anja Krøyer, Line Kenborg, Henrik Hjalgrim, Maria Feychting, Giorgio Tettamanti, The Lancet Regional Health – Europe, online July 4, 2025, doi: 10.1016/j.lanepe.2025.101363

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