There was a run of Posts about plagues a while back, where we also discussed including detailed effects:
% with no symptoms
% incapacitated
% dead
# turns for incubation
- (plague is infectious, and spreads to ships but no signs of danger until the timer expires)
Possibly even with the % incapacitated greater than 100%, since the sick have to be tended by the healthy
A nasty plague would be one with almost no deaths, but 300% incapacitation and a long incubation period... it could shut down a system or two incredibly quickly after it breaks loose, leaving the system vulnerable to invasion, and maybe even disabling a pile of defense ships (from the crew losses)