Individuals who survived cancer during childhood face a significantly heightened risk of developing severe illness from COVID-19, even many years after their initial diagnosis. This conclusion is based on a recent study conducted by researchers at Karolinska Institutet and published in The Lancet Regional Health – Europe. The findings shed light on the long-term health vulnerabilities that persist in this group, long after the apparent resolution of their primary illness. Although treatments for childhood cancer have vastly improved survival rates over the past few decades, they may leave survivors with lasting physiological impacts that compromise their ability to cope with serious infections later in life.
In this comprehensive population-based registry study, scientists investigated the outcomes of adult survivors of childhood cancer during the COVID-19 pandemic in Sweden and Denmark. The researchers examined the health outcomes of more than 13,000 individuals who had been diagnosed with cancer before the age of 20 and who were at least 20 years old by the time the pandemic began. These individuals were compared to both their siblings and a control group of randomly selected individuals from the general population matched for gender and year of birth, thereby ensuring a robust comparative framework.
Interestingly, the study revealed that childhood cancer survivors were somewhat less likely to contract COVID-19 than those in the control groups. However, the most striking finding was that, if they did become infected, they were 58 per cent more likely to develop a severe form of the illness. Severe COVID-19 was defined in the study as a case that resulted in hospital admission, admission to intensive care, or death. This suggests that although survivors may have taken greater precautions to avoid infection, their bodies were less capable of mounting an effective response once the virus had taken hold.
Dr Javier Louro, a postdoctoral researcher at the Institute of Environmental Medicine at Karolinska Institutet and the first author of the study, emphasised the significance of this outcome. “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,” he noted. This observation is particularly critical because it reframes how we assess risk: not only in terms of exposure or likelihood of infection, but in terms of the severity of the health consequences when infection occurs.
Another essential element of the study concerned geographical variation in risk, influenced by national pandemic policies. During periods of high viral transmission, such as the waves driven by the Alpha and Omicron variants, the differences in outcomes were especially stark. In Sweden, which adopted a less restrictive, recommendation-based approach to managing the pandemic, the increased risk to childhood cancer survivors was more pronounced than in Denmark, which implemented stricter, early-stage mitigation measures. This comparison suggests that public health policy can play a significant role in protecting vulnerable groups, especially when their susceptibility is not immediately apparent.
The study’s authors conclude that adult survivors of childhood cancer should be explicitly recognised as a high-risk group in the event of future pandemics or large-scale health emergencies. Their inclusion in vaccination priority lists, along with tailored guidance and protections during periods of high transmission, could be crucial in reducing the disease burden in this population. More broadly, the study underscores the necessity of considering long-term survivorship in the planning of public health responses, recognising that the shadow of childhood illness can extend well into adult life, shaping how individuals experience and survive new health threats.
More information: Javier Louro et al, COVID-19 infection and severity among childhood cancer survivors in Denmark and Sweden: a register-based cohort study with matched population and sibling comparisons, The Lancet Regional Health – Europe. DOI: 10.1016/j.lanepe.2025.101363
Journal information: The Lancet Regional Health – Europe Provided by Karolinska Institutet
