So I start with blue variants for base characteristics and silent + spread. After shit hits the fan I switch to red base characteristics + decoy and try to hide some viruses where there are less t-cells. After the immunity calms down I switch back to blue, an so on. At some point new viruses cost to much biomass and i lose. As biomass doesn't seem to be reset after each attempt, i think it's possible to achieve higher score with patience.