Not May of last year.
Well by May of this year (2021), we had over a quarter of a billion doses of effective vaccine administered to Americans.
That is a strong effect. It now overwhelms the amount of immunity developing through natural exposure. We get about 25K new cases confirmed per day, and maybe twice as many undetected/unreported. A half million to a million new first shots are given per day.
Just looking at first shots to adults, we have already passed the 60% Herd Immunity threshold calculated for the original strain (based on its replication rate 1 - 1/Ro), without even including naturally acquired immunity or cross immunity.
The vaccines have achieved dominating levels in the population. Game over. The War is won. The rest is just cleanup.