Following the COVID-19 outbreak aboard Diamond Princess, the ship underwent an extensive deep-cleaning and disinfection program in Yokohama under Japanese health-authority supervision. During the subsequent local wet-dock period, interior renewal included replacement of mattresses, pillows, linens, draperies and curtains, together with previously scheduled maintenance tasks.

Diamond Princess underwent a multimillion-dollar refurbishment in Singapore from January 19 through February 2, 2019 as part of Princess Cruises' Come Back New Promise program. Movies Under the Stars received upgraded 7.1 surround sound and new pool-deck LED lighting. The casino received new carpeting, televisions and lighting; Lotus Spa and the fitness center gained renovated treatment and salon spaces and updated equipment; Explorers Lounge, Club Fusion and Princess Theater received digital-audio upgrades; Horizon Court received new furnishings; and Japanese-style bidet toilets were installed in public restrooms and suite bathrooms.