Interviews with 59 members of the Democratic National Committee and superdelegates who will formally nominate former Vice President Joseph R. Biden Jr. in August found that the vast majority of them don’t want to risk their own health or the health of others by traveling to Milwaukee and congregating inside the convention facilities.

The reluctance was spread across all age groups and expressed by both longtime delegates and would-be first-time attendees. Even those who plan to go have reservations; one said he would haul his own boat from Tennessee and stay on Lake Michigan rather than risk a hotel room.

“I have heard from people who have gone to many conventions, people who are die-hards, saying, ‘I’m not going to that,’” said David Pepper, the Ohio Democratic Party chairman. “One thing that may drive the decision is people saying they’re not going to go.”