https://www.scientificamerican.com/article/viruses-can-help-us-as-well-as-harm-us/

This year millions of people around the world have radically changed their way of life to avoid contact with other people and, thus, the novel coronavirus. Despite social distancing, many have still gotten sick in part from other viral infections. That is because, as scientists are increasingly learning, many viruses are lurking quietly in the human body, hidden away in cells in the lungs, blood and nerves and inside the multitudes of microbes that colonize our gut.

Biologists estimate that 380 trillion viruses are living on and inside your body right now—10 times the number of bacteria. Some can cause illness, but many simply coexist with you. In late 2019, for example, researchers at the University of Pennsylvania discovered 19 different strains of redondovirus in the respiratory tract; a handful were associated with periodontal disease or lung disease, but others could possibly fight respiratory illnesses. Scientists' rapidly expanding knowledge makes it clear that we are not made up primarily of “human” cells that are occasionally invaded by microbes; our body is really a superorganism of cohabitating cells, bacteria, fungi and most numerous of all: viruses. The latest counts indicate that as much as half of all the biological matter in your body is not human.