Tuesday was a “landmark day,” as the United States reached a new Covid-19 vaccine milestone: 60% of adults have now received at least one dose of Covid-19 vaccine, according to the US Centers and Disease Control and Prevention.Tuesday was a “landmark day,” as the United States reached a new Covid-19 vaccine milestone: 60% of adults have now received at least one dose of Covid-19 vaccine, according to the US Centers and Disease Control and Prevention.