Medical data show that EBV infection in humans establishes a lifelong latent infection with a population infection rate of over 90%. That is, infection is very common in the normal population, with about 90% or more of adults seropositive for EBV. Epidemiological studies in China in the 1980s showed that 80.7-100% of children were seropositive for EBV conversion at age 3-5 years; at age 10 years, 100% of children were seropositive for EBV conversion. Most primary EBV infections are asymptomatic, especially in children under 6 years of age, but in childhood, adolescence, and young adulthood, about 50% of primary infections manifest as infectious mononucleosis. Once infected, EBV establishes a latent infection in the body’s B cells and the infected person becomes a lifelong carrier; when the body’s immune function declines and certain factors trigger it, latent EBV can be reactivated, causing viral replication and clinical disease. Since the many antibodies produced after infection are non-protective, they do not prevent the possibility of reinfection. Moreover, the individual itself is in a viral state and it is not possible to distinguish whether it is a recurrence or a reinfection.