My mother once said that time travel was both the cause and the effect of all of this.
Dr. Cassandra Railly
But none of that matters anymore. We have the virus. The Primaries sent us here to destroy it.
Once Olivia turns on her weapon, begins her Red Forest, she'll exist outside of causality. Destroying the plague won't stop her.
But it will rob of us of the only weapon we have to use against her... Time travel. The Primaries didn't send us here to stop the plague. They sent us here to release it.