Not to play conspiracy theorist advocate, but if you were developing viruses you probably wouldn’t make one big super contagious deadly virus, out of fear of exactly this happening.

You’d probably develop one very deadly one that is hard to transmit and one more minor one that is very transmissible, and work on growing those capabilities separately with separate teams. Then if you actually needed to use them for something, you’d work on combining them.

Obviously this a gross oversimplification, but the idea of “store and manage potentially life threatening things separately and only combine them when you absolutely have to” applies to all areas of defense and potentially hazardous research, so I have to imagine it would apply here too.