Former Emperor Akihito and Empress Michiko exhibited cold symptoms last month, but the octogenarians have since largely recovered, the Imperial Household Agency said Thursday.
Examinations ruled out the coronavirus and influenza as the cause of their symptoms.
The former emperor, who turned 89 on Dec. 23, developed a fever and cough one day after his birthday, while the former empress, 88, had symptoms of a cold in mid-December and exhibited them again later that month after a brief recovery, according to the agency.
After resting for the remainder of the year, the couple attended an event on New Year's Day and joined other members of the royal family, including their son Emperor Naruhito, to greet well-wishers at the Imperial Palace the following day.
The former emperor and empress, who now live in the Akasaka Estate in Tokyo's Motoakasaka district, have been refraining from their usual daily walk as a precaution, the agency said.
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