p18 is an antigen of 18 kDa codified by the BFRF3 gene. Antibody to VCA are found both in early and late EBV infection. At the time of infection, antibody of both the IgM and IgG types are detectable. After four to six months, usually, only the IgG antibody against VCA can be found. VCA-p18 can be considered to be the best dominant immunoreactive antigen for use in IgM VCA diagnosis (Wout et al., 1993, J. of Virology, p. 3908-3916).