"react fast" is correct and usable in written English.
You can use it when you want to tell someone to respond or act quickly. For example, "If you suspect the food has gone bad, react fast and throw it away."
We can react fast and allow for risk and failure".
"We need mobility and the capacity to react fast.
People react fast to both improvements and problems".
Energy storage can act as spinning reserves if it can react fast enough.
Twitter rewards those who react fast; it demands that people weigh in quickly and decisively.
Liquid organelles that react fast to stimuli lack a delimiting membrane30.
Competitive enterprises have to react fast and flexible to an increasing dynamic environment.
Now nearly 50% of UK air passengers choose the no-frills operators "because the legacy airlines don't react fast enough".
He said the security officers accompanying Kohver had not been able to react fast enough to stop the abduction.
But I don't react fast enough to prevent the water slapping me in the face as we nosedive.
However, most of these kinds of protocols are not able to react fast enough to maintain routing.
