After the first stage, or the 'Initial Infected' phase obviously it came to the second phase, the next stage of evolution. As Aziel thought back on the stronger infected soldiers with the blueish tinted irises before, he connected the newfound information with what he had witnessed and experienced.
The initial infected's main drive was to continue to spread the virus as well as amass more and more biomass from its prey, which it would then continue to use for its own individual development.
Whilst the virus had a hivemind, a connected consciousness for each of its 'drones' as it referred to them, each individual drone still had its own personal chance to grow stronger and subsequently reach a higher rank within the collective hive.
As the infected consume more organic tissue and stockpile mass, they will develop further and continue to mutate. If this is maintained for several days, they will soon reach the criteria for further growth.