The case is being studied by researchers from King's College London.
A man in Britain battled the same COVID-19 infection for nearly 18 months, the longest known continuous case since the emergence of the pandemic. According to a report in Metro, the patient died 505 days after being diagnosed in 2020.
The details of the patient have not been revealed, but doctors said the immune system was severely immunocompromised.
The doctors, however, did not reveal how old the patient was or the vaccination details.
The patient had fallen victim to 10 mutations of coronavirus, including Alpha, Gamma and the Omicron.
The case is being researched by experts from King College London and Guy's and St Thomas' NHS Foundation.
The team is studying nine patients with weak immune system because of HIV or other reasons. Four of these patients died, while two others recovered with antibody therapies and anti-viral medicines. Two other patients recovered without any treatment.
But the ninth patient is still battling a 412-day-old infection.
Immunocompromised individuals are particularly vulnerable to Covid because their body's natural defences are much weaker. Due to this, they take longer to recover and harbor the virus longer.
Researchers say this gives the virus more time to mutate inside their bodies, which can lead to the emergence of a new variant, said the Metro report.
The researchers presented their findings to the European Congress of Clinical Microbiology and Infectious Diseases in Portugal.
The research is a part of the project to understand long Covid and its impact on people. A recent study claimed that women with long Covid exhibit more symptoms than males with the syndrome.
Long-Covid is defined as persistent symptoms extending beyond 12 weeks after the initial symptoms of acute infection.