New York, Jul 6 (IANS): A cancer patient in US' Connecticut has become the second longest-known in the world to be infected with Covid as he suffered the infection 471 days, according to a pre-print study, not peer-reviewed.

An immunocompromised person in the UK is known to have been the world's longest-known Covid sufferer -- at 505 days.

A team of researchers from the universities of Yale and North Carolina found that the US patient's immune system has been weakened by cancer, providing opportunity for the emergence of genetically divergent and potentially highly transmissible variants as seen with Delta and Omicron.

Further, during the Covid infection, the person also evolved at least three distinct lineages of the virus in the bloodstream.

"Each of the lineages was genetically divergent enough (about 20-40 mutations from the original virus) that they would be classified as separate lineages if they were to spread into the wider population," Chrispin Chaguza from Yale school of Public Health wrote on Twitter.

"Our study provides evidence that chronic SARS-CoV-2 infections could be a source for the emergence of genetically diverse variants capable of causing future Covid-19 outbreaks. We have seen this scenario recently with the emergence of Omicron sister lineages (BA.1 and BA.2)," Chaguza added.

Scientists have for long stated that immunocompromised people serve as hosts for Covid's evolution. Previously, scientists in South Africa have speculated that Omicron may have evolved mutations in one person, as part of a long-term infection.

The person, in 60s, was chronically infected with B.1.517 with a history of large B-cell lymphoma and had undergone a stem cell transplantation in 2019.

But in early 2020, the patient's disease relapsed and was started on a new chemotherapy regimen. The patient was noted to have persistent but improving disease up until November 2020 when it started to relapse again.

The team collected 30 swab samples from the patient between February 2021 and March 2022, that is from day 79 to 471. They concluded that the virus might be evolving twice as fast inside the patient as it did in the general population.

"We showed accelerated SARS-CoV-2 evolution during the chronic infection, approx twice as faster as the parental B.1.517 strain and the global SARS-CoV-2 evolutionary rate, suggesting that it could be a mechanism for the emergence of genetically divergent variants," the team wrote in the study.

The patient first tested positive for Covid in November 2020, and continued to be positive for the virus at least till March this year.

"The patient continues to test positive for SARS-CoV-2 471 days, and counting after the initial diagnosis," the researchers said.

Besides the initial presentation of several days with mild upper respiratory tract symptoms not requiring oxygenation or hospitalisation, the patient has remained asymptomatic for much of the duration of the SARS-CoV-2 infection.

The only Covid treatment the patient received was a bamlanivimab monoclonal antibody infusion on day 90, after which the patient did not wish to obtain any additional Covid-19 therapies or vaccines.