Nature: Most people’s viruses remain “dormant”

Even completely healthy individuals constantly carry viruses in their bodies—often in significant amounts. This conclusion comes from a study analyzing data from nearly one million people. The work was published in Nature.

The research was conducted by a team led by specialists from Harvard Medical School. Scientists examined blood and saliva samples from over 917,000 people and assessed the so-called viral load—the amount of viral DNA in the body.

“We’ve reached a stage where we can use human genetics to answer fundamental questions about how viruses cause disease,” said geneticist Nolan Kamitaki.

It turned out that in most people, viruses remain “dormant”: they are present in cells but do not cause symptoms. The immune system keeps them in check, preventing the infection from turning into illness. Analysis revealed 82 regions in the human genome associated with viral load levels. The major histocompatibility complex (MHC)—a key system regulating immune response—plays a particularly important role.

Scientists also identified patterns for specific viruses. For example, Epstein–Barr virus (EBV) is more common with age, with activity higher in winter and lower in summer. Other viruses are more stable. Using Mendelian randomization, researchers evaluated links between viruses and diseases. They found that a high Epstein–Barr viral load increases the risk of developing Hodgkin lymphoma. No similar association was found for multiple sclerosis, although EBV is considered a factor in its development.

“This result shows that it’s not just the infection itself that matters, but also how the immune system responds to it,” Kamitaki explained.

In addition to genetics, external factors—such as age, sex, and even smoking—affect viral levels. Most viruses were found more frequently in men.

As geneticist Steven McCarroll noted, the results highlight how closely genetics, lifestyle, and immune function are connected: “It’s remarkable how much DNA can tell us about biological processes and how our habits and genes shape them.”

The authors emphasize that the study only examined DNA viruses. In the future, scientists plan to study RNA viruses, including coronaviruses, to get a more complete picture of the “hidden” viral world within humans.

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