Japan needs to thoroughly review its response to the pandemic and fully prepare for the next public health crisis, Shigeru Omi, the government's top COVID-19 adviser, has said.

On Monday, the government downgraded the legal status of the disease to the same level as seasonal flu.

"There was ambiguity and trial and error" in role-sharing between the government and experts, Omi said in an interview looking back at the past three years of Japan's experience in dealing with the pandemic.