In the US, Southern states have the lowest vaccination rates, while North Eastern states have the highest vaccination rates. This pattern appears to be largely down to partisanship: Republicans are less likely to be vaccinated than Democrats.
At the end of August, when the Delta variant was dominant, case rates were highest in Southern states like Alabama, Georgia and Florida. Meanwhile, they remained low in North Eastern states like New York, Massachusetts and New Jersey. This is shown in the map below, which gives the official case curve for each state up to 26 December:
The much higher case rates in the South seemed to provide evidence that the vaccines stop infection (in addition to protecting against serious illness and death). Hence, it was believed, vaccine passports will help to curb transmission.
Fast forward three months, and the situation is rather different. Infections are now surging in the North East. This has led to the somewhat peculiar situation whereby case rates are highest in some of the mostvaccinated states. See the chart below, based on data from the CDC: