Answer:
Well there is controversy over wether or not"solanum"( also known as T-virus ) really exists, but if you can get it these ar some of the ways.
Open wounds brushing onto the infected can result in infection, as well as being bitten by them. Eating infected flesh will not result in reanamation, but death, as infected flesh is very toxic. Solanum is not air or waterborne. There is not a vaccine because, even the smallest trace of the virus in the bloodstream results in a coma, death and reanimation within 24 hours.