The number of rubella patients reported in the nation this year stands at 362, nearly four times the number seen the previous year, with many of the cases located in Tokyo and its vicinity, the National Institute of Infectious Diseases said Tuesday.

The institute is warning a potential rubella outbreak could even affect the 2020 Games, and is urging people — mainly men in their 30s to 50s — to get vaccinations, as many have not been vaccinated fully against the disease.

The latest report through Sept. 2 showed 75 cases had been newly reported in a week, down from 97 the previous week. Of these, 28 were in Tokyo, followed by 11 in Chiba Prefecture, eight in Kanagawa Prefecture, seven in Aichi Prefecture and five each in Ibaraki and Saitama prefectures.

Rubella is highly contagious and is often transmitted through coughing and sneezing. It can have a serious health impact if contracted by women in the early stages of pregnancy as it tends to cause birth defects such as heart disorders, hearing impairments and cataracts in babies.

Vaccination is effective in preventing infection, but women who are already pregnant cannot be vaccinated as the vaccine itself is feared to have an impact on the child.

Japan saw a major rubella outbreak in 2013, with over 10,000 people infected. Cases of infection have since declined but there has been a resurgence since late July this year, with many of the patients being men in their 30s and older.