New research suggests age-related changes in blood cell chromosomes are a marker of impaired immunity.

A person’s risk of severe infections increases dramatically as they grow older, but scientists do not yet understand how age might be linked to weakened immunity. Now, research shows that certain age-related changes in blood cells are associated with a higher risk of a range of severe infections including severe COVID-19, other pneumonias, and sepsis.

Researchers analyzed genetic and clinical data from nearly 800000 patients from around the world. They discovered that people with a specific type of acquired rearrangement in the chromosomes of their blood cells, called mosaic chromosomal alterations (mCAs), were nearly three times more likely to develop sepsis and two times more likely to get pneumonia than those without mCAs. These genetic changes accumulate in blood cells with age and often indicate a common condition in the elderly called clonal hematopoiesis.