An 89-year-old Dutch woman is the first confirmed case of a person dying from a COVID-19 reinfection, according to the Oxford University Press.

The woman had a relatively easy first infection, in which she spent five days in the hospital earlier this year exhibiting mild symptoms including a fever and cough and testing positive for the coronavirus. Her symptoms subsided, with the exception of chronic fatigue, and she tested negative.

Two months after her first infection, and two days after starting a round of chemotherapy treatment for a rare type of bone marrow cancer called Waldenstrom’s disease, she tested positive for COVID-19. Medics tested the genome makeup of the new virus to confirm it was indeed a new infection rather than a case of the woman not shedding the virus the first time around.

Her second bout with COVID-19 was far worse, including fever, cough and dyspnea with an oxygen saturation level of more than 90 percent. On the fourth and sixth days of her new infection, she tested negative for antibodies, according to the Oxford report. “On the eight day, the condition of the patient deteriorated,” the report states. “She died two weeks later.”

COVID-19 has a low reinfection rate, according to the Oxford researchers, who say just 23 cases of confirmed reinfection have been reported worldwide. In all previous reinfections, the patients all survived.

The researchers say that reinfections occur “once antibody titers decrease and immunity wanes,” which calls into question the effectiveness of vaccines if antibodies are not long-lasting.

In rare cases, including a 25-year-old reinfected man from Nevada with no underlying conditions, the new infection was far worse than the first round of the virus. A 33-year-old Hong Kong resident was the first confirmed case of reinfection four months after testing negative for COVID-19 earlier this year. There have been several cases of people taking months to shed the virus, which the Oxford researchers say can be mistaken for reinfection, and thus suggest a full study of the virus genome in all suspected second infection cases.