I think the problem is that the virus is so mild. You can't spot a lot of cases, so e.g. someone gets on a plane and is not showing symptoms and a few days late

I think the problem is that the virus is so mild. You can't spot a lot of cases, so e.g. someone gets on a plane and is not showing symptoms and a few days later in Italy they get sick or infect others without realising they're ill.