We report a prospective study of 56 pregnant women inadvertently vaccinated with rubella vaccine during the 2006 campaign performed in Argentina. Of these patients, 48 (87%) were immune, whereas the remaining 9 (16%) were susceptible. In the latter group, 7 presented with a primary reaction to the vaccine confirmed through immunoglobulin (Ig) G antibody avidity testing or seroconversion of IgG titers. During the clinical and laboratory follow-up, newborns did not present evidence of infection or malformations compatible with congenital rubella syndrome. [ABSTRACT FROM AUTHOR]