In regard to biological weapons, they have the issue of being easy to backfire. I'm not mentioning any lab theories related to events from the recent years as a

In regard to biological weapons, they have the issue of being easy to backfire. I'm not mentioning any lab theories related to events from the recent years as an example of possible developments. There are other factors like not being very effective against people in the prime of their health like those serving in an army and the whole thing where nobody internationally likes the guys spreading illiterate viruses which do not respect boarders and kill outside of war zones.