IN comparative studies on the antibody status with age, such as the Swedish investigation illustrated in the Figure, rubella immunity has been found to be acquired relatively slowly, at least when compared to measles immunity1,2 or antibodies to the Epstein-Barr virus.3
A consequence of the relatively slow acquisition of rubella immunity is that a sizeable proportion of pregnant women lack rubella antibodies.2 It would seem that all of them should run a risk of acquiring rubella and of transmitting the virus to their fetuses. The situation is more complicated than that, however, since, at least in some population groups,4,5 rubella antibody levels tend to drop with age and increasing time after infection. Depending on the sensitivity of the techniques employed, a varying proportion of the apparently susceptible women may actually possess a low-level immunity. The question is to what extent such low-level immunity protects against reinfection