Princess Yoko Develops Pneumonia After Contracting COVID, Transferred to New Hospital for Treatment

Princess Yoko of Japan has developed moderate pneumonia after testing positive for COVID, the Imperial Household Agency confirmed.

The agency said that Yoko, 38, was diagnosed with the virus on Tuesday after experiencing a sore throat the day prior. The princess was later admitted to a hospital inside Imperial Place before being transferred to the University of Tokyo Hospital for further treatment.

She is the first member of the Imperial House of Japan who had been infected by the virus. Her illness comes as Japan is hit with a "sixth wave" of the pandemic involving the latest variant of the virus, Omicron.

Her older sister, Princess Akiko, whom she had encountered several days before, tested negative for the virus.

The agency shared that none of her staff or other royal family members have experienced any illness or were infected by COVID.

Can't get enough of PEOPLE's Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more!

It is still unclear how Yoko contracted the virus since the princess has not attended any gathering recently. However, she did participate in a ceremony to commemorate a late emperor at the palace on Jan. 30.

The news of her diagnosis comes after royal members worldwide had also tested positive for the viral disease, including Princes Charles and his wife, Camilla from the British monarchy, Denmark's Queen Margrethe, and Spain's King Felipe.

RELATED VIDEO: Prince Charles Tests Positive for COVID, Now Self-Isolating, Clarence House Announces

The princess plays an active role in her community. In addition to leading a Tokyo-based social welfare corporation Yuai Jujikai, she also serves as the honorary president of Japan Universal Sound Design Association, a nonprofit organization that assists people with hearing impairment.

Yoko is one of the two daughters of Prince Tomohito of Mikasa. Her dad, who passed away in 2012, was a first cousin of Emperor Akihito and previously sixth in line to the Japanese Throne.

As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.