A new poll shows that most Americans who haven’t been vaccinated against COVID-19 say they are unlikely to get the shots. Most of them also doubt they would work against the aggressive delta variant despite evidence they do. Those findings underscore the challenges facing public health officials as soaring infections in some states again threaten to overwhelm hospitals. The poll conducted by The Associated Press-NORC Center for Public Affairs Research found that 35% of adults who have not yet received a vaccine say they probably will not, and 45% say they definitely will not. Just 3% of unvaccinated Americans say they definitely will get the shots, though another 16% say they probably will.