The pattern of antibody response to different EBV antigens helps distinguish acute or subclinical infections from post infections with the virus. IgM antibodies to viral capsid antigen (VCA) appear early in the course of the infection, but at the time of clinical symptoms, IgG levels to VCA are quite high. Thus, paired sera at the time of clinical infection do not help diagnose the disease. In contrast, antibodies to EB nuclear antigen appear months after the infection. Antibodies to early antigen appear in about 70% of primary infections and are usually indicative of an acute infection.