Amid the latest surge in covid-19 cases and hospitalizations, the United States on Tuesday hit a milestone that some thought was unattainable: 90% of people 65 and older are at least partly vaccinated against the disease. “This really shows our elders are wiser than the rest of us,” said Dr. David Wohl, professor of medicine in the division of infectious diseases and director of the vaccine clinics at the University of North Carolina School of Medicine.