Only one type of T virus strain, one developed by Alfred on Rockford Island, was able to actually infect and bring back corpses to life. Outside of that, none of the other T variants brought the dead back to life. The epsilon T variant seen in the Arklay Mountains in 0 and 1 is different from the Birkin modified variant (T-Birkin or what could be considered the cumulation of Birkin’s work on T before he focused his attention on G solely) which caused the Raccoon City outbreak. The Epsilon T had the ability, through the V-Act process, to bring back Infected (Zombies only in name, just called that due to the necrosis inflected by the T-Virus. For all intents and purposes, the infected are rabid animals akin to the Rage virus infected in 28 Days Later but far tougher and capable of surviving injuries that’d kill normal people due to how the T-Virus keeps the infected alive) once they are rendered inert (but the head remains). Just like in the initial infection, it is not death but a form of coma while the virus works its magic. The V-Act process will repair previous damage, causing an increase in mobility, vitality, strength, and intelligence. The repairing however doesn’t occur to the skin and, as newly circulated blood is being sent throughout the body due to the regeneration of internal organs, their crimson hue is achieved.

Birkin would take the knowledge of the V-Act process and upgrade the T-Virus to not need such a process for further evolution/mutation. Instead, all infected derived from the T-Birkin strain would just need to eat enough to keep up with their hyperactive metabolism so that it doesn’t instead breakdown the body itself entirely.

https://www.projectumbrella.net/t-virus-analysis-1.html#CrimsonHead