Fetal risk associated with rubella vaccination during pregnancy

Costa Rica implemented a nationwide measles-rubella vaccination campaign among men and women (15-39 years old) in May 2001. A protocol was developed to follow-up the vaccinated women who were unknowingly pregnant, to determine the risk of congenital rubella syndrome (CRS) or congenital rubella infection only associated with the administration of the rubella vaccine RA27/3 during pregnancy.

To classify the prevaccination maternal immune status, a serum sample was taken at the initial evaluation to detect IgM and IgG rubella antibodies (enzyme-linked immunosorbent assay). All pregnancies were followed up and all newborns were evaluated. A cord serum sample of their children was taken at birth. We calculated odds ratio, OR (95% confidence interval, 95% CI) associated with miscarriage, stillbirth, prematurity, low birth weight, and the presence of defects compatible with CRS.

The prevaccination immune status was established in 797 women and 1191 mother and child pairs were analyzed. Adjusted OR for miscarriage (OR = 0.60, 95% CI = 0.26-1.39), stillbirth (OR = 1.32, 95% CI = 0.10-16.81), prematurity (OR = 0.25, 95% CI = 0.03-2.39), low birth weight (OR = 0.25, 95% CI = 0.03-2.23) and defects compatible with CRS (OR = 1.09, 95% CI = 0.34-3.54) showed no association between immune and susceptible maternal status. There were no cases of CRS and no children were IgM positive.

No adverse pregnancy outcome such as miscarriages or CRS was documented in women who were vaccinated and unknowingly pregnant. These results support RA27/3 rubella vaccine safety.