After the great financial crisis, people turned to their government for help. Many become homless and move into fema camps where they ingest the virus through food, water, air-conditioning etc, basically fully exposed. Then after they are "rehabilitated" along with "startup funds", they are re-introduced into the general public and are highly contagious in an ingenious time released symtomatic dormant state...until death. Also, back while they were living the "good life", they are actually infecting all those who come into contact with them and everything they touch. Remeber Rick said after the CDC, " We're all infected". My other thorey is aresol exposure from Chemtrail spraying we currently see in our skies on a daily basis. Population control.