The fresh rubella outbreak spreading quickly nationwide poses the greatest threat to fetuses, according to the National Institute of Infectious Diseases.

If a woman catches rubella in the early stages of pregnancy, her child can suffer hearing, heart and eye defects. Five such cases were reported during last year's epidemic and one has already been reported this year, the institute said.

On Jan. 29, the health ministry issued a nationwide alert about the potential for another epidemic and recommended that prefectures and other local governments start promoting vaccinations. The case count in January has already surpassed the yearly average.