CMV (Cytomegalovirus)

Cytomegalovirus (CMV) is a very common beta-herpesvirus that sets up lifelong latency after the first infection. Seroprevalence runs from about 40 to 70% in high-income populations (rising with age) to over 90% in parts of Africa, Asia, and South America. Because your body never fully clears CMV, your immune system keeps a large, chronically active CD8+ T-cell force aimed at the virus. This is called 'memory inflation'. Over decades, these CMV-specific CD8+ cells expand and occupy a growing share of your total T-cell pool. They crowd out naive cells and narrow your immune range. That is linked to weaker vaccine responses, frailty, and higher death rates in older adults. CMV positivity is considered one of the strongest external drivers of immunosenescence. It is now built into immune-age scoring approaches like the 'immune risk profile'.

Last reviewed: June 22, 2026

This definition is educational and is not medical advice, a diagnosis, or treatment. Talk to a doctor about any health decisions. Read our full medical disclaimer