Yes but having all the tools does not mean it knows when to use...

Yes but having all the tools does not mean it knows when to use them.
Until your body sees the invading virus as a threat it will not fight it.
Clearly some peoples defence systems are quicker at recognising an invading threat than others are.
So we start fighting the invader at various times and for some that comes too late.
That is where vaccination helps out by making your body aware that this virus is a threat so it starts fighting it straight away.