As you might expect, there's a clear drop-off in new COVID cases per capita as the vaccination rate of the counties goes up. There seems to be a slight drop-off starting around 50% fully vaccinated, followed by a steep drop-off starting around 65% vaxxed. There's a third drop-off at around 75%, but there's literally only a handful of counties which have achieved that high a vaccination rate so far anyway.
HOWEVER, there's one major outlier over the 65% threshold...Miami-Dade County.
According to the Centers for Disease Control, Miami-Dade has fully vaccinated 68% of their entire population (1.84 million out of 2.72 million residents). I use the slightly lower official 2020 U.S. Census popualtion count for Miami-Dade County (2,701,767), which makes the vaccination rate slightly higher still: 68.24%.
For the past couple of months now, most of my COVID scatter-plot charts...whether measuring vaccination rates, new case rates or new death rates...have been based primarily on partisan lean. That is, at both the state and county levels, I've been using the percent of the 2020 Presidential vote won by Donald Trump as the basis for comparison.