Why are there no infected transports between two 100% infected countries?
Your disease type is Fungus
Fungus is the only disease type to have a base transmission rate of 0.1 for air and sea (and land). This means that even if 100% of the population is infected, there's only a 10% chance that a plane or ship originating from that country will be carrying the disease.
For all other disease types, if a country is 100% infected, all planes or ships will carry the disease.