D. HERD IMMUNITY AND SARS-COV-2 Early in the pandemic, the target herd immunity threshold for SARS-COV-2 was estimated to be about 60 to 70 percent of the population based on the contagiousness of the original version of the virus. However, variants now circulating in the United States have increased this threshold. The B.1.1.7 (Alpha) variant first identified in Britain, is about 50 percent more transmissible and experts increased the herd immunity threshold to at least 80 percent. Now, there is an even more contagious variant called the B.1.627.2 (Delta), and the calculation will have to be revised upward again. Your instructor will display a chart from the online source "Our World in Data" that shows the Share of People Vaccinated Against COVID-19. 1. What percentage of the U.S population has been fully vaccinated against COVID-19