Increased risk of severe COVID-19 in individuals with chronic lymphocytic leukaemia
A doctoral thesis from Karolinska Institutet shows that people with chronic lymphocytic leukaemia (CLL) were at greater risk of severe COVID-19 than the general population. The findings also suggest that repeated vaccinations can strengthen immune responses and help protect against serious disease.
Chronic lymphocytic leukaemia (CLL) is a type of blood cancer that weakens the immune system and increases susceptibility to infections. In her doctoral thesis, Lisa Blixt at the Department of Oncology-Pathology investigated how people with CLL were affected by the COVID-19 pandemic and how their immune system responded to both infection and vaccination.
One study followed 60 patients with CLL who contracted COVID-19 during the first year of the pandemic. Of these, 77 percent required hospital treatment and 23 percent died. Among those who were subsequently assessed, 82 percent developed antibodies against the virus, and the same proportion showed evidence of T-cell immunity.
The thesis also found that people with CLL generally mounted weaker immune responses to COVID-19 vaccination than healthy individuals. However, patients who had previously had COVID-19 and were later vaccinated developed substantially stronger immune responses, which were further enhanced by additional vaccine doses.
“Many patients were able to build up a stronger immune response through repeated exposure to the virus via vaccination,” says Lisa Blixt.
A nationwide registry study involving more than 6,300 people with CLL showed high uptake of the initial vaccine doses, but lower uptake of later booster doses.
Another registry study found that people with CLL faced a higher risk of COVID-19-related hospitalisation and death than the general population. Although this risk declined as the pandemic progressed, it remained lower among those who had received additional vaccine doses.
The thesis was supervised by docent Lotta Hansson at the Department of Oncology-Pathology. Lisa Blixt defended her thesis on 23 October 2026.