Dr. Philip Griebel and colleagues at the University of Saskatchewan's Veterinary Infectious Disease Organization successfully immunized fetal lambs against a herpesvirus by injecting DNA vaccine into amniotic fluid in the fetal animals' mouths. The procedure, performed during the third trimester, elicited a strong immune response systemically and in the oral cavities of all of the lambs. Viruses transmitted from the mother at or shortly after birth typically enter an infant's body through mucous membranes in the mouth, nose or eyes.

It has long been thought that fetuses do not have fully developed immune systems, said Griebel. Thus, researchers believed in-utero vaccination would produce a tolerance rather than an immune response to an introduced pathogen. "We showed quite clearly that this is not the case," said Griebel.

If the findings, published in Nature Medicine (2000;6:929-32), are borne out by further research, the transmission of disease from infected mothers to their children during birth or breast-feeding could eventually be prevented. To date, providers have tried to reduce risk of disease spread by delivering babies by cesarean section or by treating the mother or baby with antibiotics.