Vaccine might be playing somewhat of a role but it's strange. Look at Michigan for example, they had a surge yet despite having a decent amount of vaccinateds, yet other states with fewer vaccinateds than Michigan didn't see a surge.

Also there were several countries which avoided getting hit bad in their first waves... Why is that? Maybe certain conditions which we aren't cognizant of were not present during that time as they were during later waves. Now apply the same to the U.S.

Another factor to consider is asymptomatic spread could be increasing even if symptomatic spread is not. If people have some immunity that prevents symptoms but not enough to prevent infection then we could be on the verge of new variants emerging under selection pressure within the coming weeks or months in those of the vaccinateds or those who have been infected previously.