It was not the grand affair of their dreams. She wore a borrowed maxi skirt. He felt the absence of his sister and grandmother. They swapped mood rings bought days earlier on Canal Street.

Dana Cohen and Adam Quinn had planned a spring wedding, but instead married on Friday at the drab Brooklyn Municipal Building — so Mr. Quinn could add his new wife to his health insurance.

“We don’t know what the world will look like in three months,” said Mr. Quinn, 38, who works for the Cooper Hewitt, Smithsonian Design Museum.

That sentiment reverberates along the subways and sidewalks of New York City, where the usual throngs and random interactions with strangers — the very things built into the magic and texture of this city — are approached with an unsettling caution in the age of the new coronavirus.