Rubella vaccinations may be safe during early pregnancy, a new study from the University of Toronto in Canada has reported.
The findings, presented recently at the annual meeting of the American Society for Clinical Pharmacology and Therapeutics in Orlando, Florida, raise doubts about the need to consider abortion because of exposure to the vaccine in early pregnancy. They also challenge the long held belief that it is essential to avoid vaccinating pregnant women against rubella for fear of the vaccination itself inducing the congenital rubella syndrome.
Rubella is a togavirus that usually causes mild illness, characterised by an upper respiratory infection, measles-like rash, fever, and lymphadenopathy. Complications of the disease include arthritis, encephalitis, and congenital rubella. Congenital rubella occurs when a woman contracts the rubella virus during her first trimester of pregnancy.
About 85% of women who catch rubella in the first trimester transmit it to their fetus. Hallmarks of the syndrome in the child are sensorineural deafness; congenital heart defects; learning difficulties; eye defects such as cataracts, glaucoma, retinopathy, and microphthalmos; and bone defects. Hepatosplenomegaly and miscarriages are also common.
As the rubella virus is so virulent early in pregnancy, the vaccine, which is composed of weakened live virus, is not advised during that time. In addition, women who receive the vaccine are cautioned to avoid conceiving for three months.
Retrospective evidence, however, has suggested that the risk of the syndrome developing after vaccination early in pregnancy is small. The US Centers for Disease Control and Prevention maintained a register of pregnant women who inadvertently received the vaccine between 1979 and 1989 and found no cases of the syndrome in the newborn infants of the 321 women enrolled.
The current study, led by Dr Zina Levichek of the Motherisk Program at the University of Toronto in Canada, compared the rates of fetal malformations in the infants of 94 women who mistakenly received rubella vaccinations while pregnant with 94 pregnant women who were not vaccinated during pregnancy.
The rate of fetal anomalies was similar in both groups. In addition, no significant differences existed in miscarriage rates, birth weight, or developmental milestones between the two groups. Hearing test results were also equivalent across the groups.
The only significant difference was the higher rate of abortions in the group who received vaccinations during pregnancy.
Figure.
NIBSC/SPL
Electron micrograph of rubella viruses