Epidemic surges don’t happen instantaneously. Even if you didn’t get the vaccine at all, and didn’t follow any of the guidelines, there’s still a fairly high chance that you’d luck out and not catch the disease, even four weeks into a surge.
Without the vaccine, but with other reasonable precautions, that chance of lucking out is higher.
And with the vaccine, even in the time frame before you’re considered “fully vaccinated”, it’ll still provide partial protection.
Starting a vaccine right at the start of a surge isn’t a guarantee of protection. But it definitely, unambiguously, improves your odds.