The guidance means that millions of fully vaccinated Americans can begin returning to pre-pandemic activities, including in-person school and work, which many have eschewed since last March. The country is seeing the lowest number of new daily cases it has had in eight months, and deaths have decreased from a high of about 3,000 per day on average in January, to about 600 per day, as many of the most vulnerable, including the elderly, have been inoculated.