ZURICH/GENEVA (Reuters) - Japan may have to ramp up its measures to tackle COVID-19 after cases have been found in some parts of the country with no known links to other outbreaks, the World Health Organization said on Friday.

“Japan has seen cases of COVID in three prefectures including Tokyo that are not linked to known chains of transmission,” Michael Ryan, executive director of the WHO Health Emergencies Programme told a press conference. “That is not good, but they are looking.”

“The data I seen this morning reassures me they are very aggressively following this,” he said, but Japan may have to scale up measures in some prefectures, he added.

Japan, with its teams of “cluster busters” has gained a lot of very useful information, including that only one in five infected people spread the disease, Ryan said.