The 404 injection's effects are actually similar to those of anti-aging injections produced by a few cutting-edge biological labs nowadays, where injections worth hundreds of thousands or even millions can delay physical aging and improve body fitness.
However, these anti-aging injections have short-lived effects and require many supplementary measures; the 404 injection, once administered, can at least maintain its effect for 10 years without side effects, which is almost equivalent to extending life by another ten years.
But this alone wasn't worth the more than 4 billion spent by the base; what's most important is that through the research on the 404 injection, the biological lab figured out some of the action mechanisms of its predecessor, the 304 injection, which is far more valuable than the injection itself.