The US marks a vaccine milestone, but one expert warns that the coronavirus Delta variant has a worrying impact on patients

As President Joe Biden celebrated America’s 300 million vaccine dose milestone Friday, experts warned that the spread of coronavirus variants could spur a surge in troubling new cases if more people don’t get inoculated.As President Joe Biden celebrated America’s 300 million vaccine dose milestone Friday, experts warned that the spread of coronavirus variants could spur a surge in troubling new cases if more people don’t get inoculated.