Problem: Tom has just been exposed to the measles virus, and he can't remember if he has had measles before or if he received a vaccination when he was a kid. He asks you if there is any way he can tell if he has been previously exposed or if he is going to get sick. In the graph "b" indicates the IgG levels that were measured in Tom's blood after his exposure to the virus. How can you know by looking at the graph if Tom had the measles? Antibody concentration in serum IgG IgM Time (weeks) IgG laM Time (weeks) if Tom has previously had the measles, there should be a significant amount of IgG antibody in his blood if Tom has previously had the measles, there should be a significant amount of IgM antibody in his blood if Tom has previously had the measles, the levels of IgM and IgG should be the same. There is no way that Tom can know if he had the measles by checking antibodies levels in his blood.