A positive rubella virus IgG antibody is caused by having been infected with rubella or having received the rubella vaccine. This is an antibody that has been present in the body for a long time, and its presence indicates that the body has acquired immunity to the rubella virus, which can occur after a rubella vaccination. If you have had rubella before, the body will also have acquired lifelong immunity and this antibody will be positive. IgG antibodies can also be positive if you are currently in the midst of rubella disease. If you can check the titer, there is a fourfold or more increase in the titer of the antibody at the beginning of the disease and at the end of the disease, and it is possible to diagnose rubella by the symptoms. Antibodies to the rubella virus include IgM in addition to IgG, and a positive IgM is indicative of a current rubella infection. If IgM is negative and only IgG is positive, it is simply a case of a previous infection or vaccination that has now acquired immunity to the rubella virus.