Spread of the Delta variant may make it even harder to reach herd immunity, expert says

With so many areas in the United States with low vaccination rates, the spread of the Delta variant of the coronavirus will make it that much harder for the country to reach herd immunity, a top expert says.With so many areas in the United States with low vaccination rates, the spread of the Delta variant of the coronavirus will make it that much harder for the country to reach herd immunity, a top expert says.