Ever since she got the coronavirus vaccine in February, Ms. Duncan, who works in hospital management, has insisted she run their errands alone. When she goes shopping, Mr. Duncan, who is unvaccinated, stays home.

Mr. Duncan, 44, said he feels gratitude but also guilt, and that tension has altered the dynamic of their marriage. “She has to take risks and chances on her own, when that’s my partner, that’s my honey.”…

For others, like Mr. Duncan in Harlem, the situation has created a strain. He feels that he is failing in his duty as a husband, he said, when his wife asks him not to join her on the grocery run. “She believes she is protecting me, and it is the right thing to do, and I feel like I don’t want her to,” he said.

He added: “It takes a lot from the relationship.”