Interferon studies with Japanese and U.S. rubella virus strains

Japanese strains of rubella virus have been claimed not to be teratogenic, and tests on three Japanese strains showed that they induced high levels of interferon in human placental cell cultures obtained from conceptuses ranging from 13 to 24 weeks' gestational age, whereas two strains derived from the U.S.A. induced low levels. Both Japanese and U.S. strains induced similar but low levels in fetal lung cell cultures and leucocyte preparations. A representative Japanese strain and a U.S. strain were both interferon-sensitive. If indeed a strain can be shown to be non-teratogenic it could lead to an alternative, safer rubella vaccine.