The Epstein-Barr virus (EBV) that causes mono is extremely common. Around 90% of Americans are infected with it by age 35. Not everyone who has the virus develops mono symptoms — some people only carry the virus.

Is everyone a carrier of mono?

To make things even more confusing, some people can carry the virus without ever getting any mono symptoms. So they may not know they have been infected, but they can still pass it to others. In fact, most people have been infected with EBV by the time they reach adulthood.

Do you always have mono?

Most people who have mono (infectious mononucleosis) will have it only once. But rarely, mononucleosis symptoms may recur months or even years later. Most cases of mononucleosis are caused by infection with the Epstein-Barr virus (EBV).