A cancer survivor carried the coronavirus for almost a year in the world's longest-ever active COVID-19 case

• A 47-year-old woman carried the coronavirus for at least 335 days, a new case study found.
• She was immunocompromised following a blood cancer treatment three years prior, per the study.

A cancer survivor was found to have carried the coronavirus for at least 335 days in the longest ever documented case of COVID-19 to date, a new study said.

The findings were published as a pre-print on Medrxiv earlier this month. It has not been peer-reviewed.

The patient, a 47-year old woman who has not been named, was first hospitalized with COVID-19 at the National Institutes of Health campus in Bethesda, Maryland, in the spring of 2020, Science News reported.

After ten months, during which she showed mild or no symptoms of the coronavirus, her doctors found that she was still testing positive for the virus, the study said.

The woman had been immunocompromised after a successful blood cancer treatment three years prior left her with low levels of B cells, which produce antibodies, the study said.

She continued testing positive for the coronavirus, which her doctors thought were false positives picking up on harmless bits of the virus left after the infection was cleared, according to the study.

When the woman's viral load rose again this March, the doctors sequenced its genome. They found that it was very similar to the coronavirus she was carrying ten months earlier and was unlike any strain circulating in the general population at the time, the study said.

The woman received treatment and finally cleared the infection in April, 335 days after she was first tested, the study said. She has now had multiple negative COVID-19 tests, Science News reported.

Studies like this one provide information about COVID-19 infection for people with a weakened immune system.

Immunocompromised people are less likely to mount a strong response to COVID-19 with two doses of vaccine, leaving them more vulnerable to infection. US regulatory agencies in August approved a third dose of vaccine for immunocompromised people in the hope it would help bolster their immune response.

These types of studies also help scientists understand how the virus evolves. For instance, a study on a woman with HIV who carried the coronavirus for 216 days found that it had mutated at least 30 times.