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Signs for the COVID-19 Vaccination Centre at the Royal Free Hospital in London, are seen on Dec. 7, 2020.

Signs for the COVID-19 Vaccination Centre at the Royal Free Hospital in London, are seen on Dec. 7, 2020. (Dominic Lipinski/Pool)

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Researchers in Britain say they have used genetic sequencing to help cure a man who was infected with the coronavirus for more than 411 days.

The 59-year-old patient, who had a weakened immune system due to a kidney transplant and the use of an immunosuppressant drug, initially tested positive in December 2020.

After further tests in February 2021 and January 2022 came back positive, the team in London carried out a genetic analysis of the virus, which showed that the same strain was present at each stage, with only minor variations - meaning that the patient was suffering from a chronic coronavirus infection, rather than multiple new infections.

Chronic coronavirus infection is distinct from long covid, in which people suffer from persistent symptoms and long-term effects after being infected with the virus that causes covid-19.

"Nowadays, everyone is infected with omicron, but when we looked at his virus, it was something that existed a long time ago - way before omicron, way before delta and even before alpha. So it was one of those older, early variants from the beginning of the pandemic," Luke Blagdon Snell, a specialist in infectious diseases and a researcher on the case, told The Washington Post on Friday.

Because the patient was experiencing only mild or intermittent symptoms, he had been ineligible for treatments used to prevent or treat severe covid.

The results of the genetic sequencing showed that the man had been infected with the B.1.177.18 coronavirus variant, which was present in Britain in late 2020. The team was therefore able to give the patient a combined antibody treatment shown to be effective against that strain.

The case was among several highlighted by Snell and the team of researchers from Guy's and St Thomas' NHS Foundation Trust and the Department of Infectious Diseases at King's College London in a preprint article published in the peer-reviewed Clinical Infectious Diseases journal on Thursday.

Although the more-recent variants now dominant in Britain do not respond to the antibodies used in this case, the findings show the potential for individualized therapies in patients with chronic coronavirus infections. The process of genome sequencing outlined in the paper offers results within 24 hours, allowing medical teams to respond quickly to patients' needs.

In two other cases highlighted in the report, genetic sequencing showed that patients suspected to be suffering from prolonged infection had in fact been reinfected with a newer strain of the virus. Their doctors were therefore able to alter their treatment plans accordingly.

Genome sequencing has been used throughout the pandemic to identify new variants and sub-strains, such as omicron, which was first detected by scientists in southern Africa in November 2021.

It is unclear how prevalent chronic coronavirus infections are. The longest case known to date was in a patient who tested positive for 505 days before dying and was treated by the same teams.

"But there's definitely a difference between a normal community infection which resolves within two weeks," as happens in most cases, and the small proportion of immunocompromised patients who are at risk of a chronic infection lasting more than six weeks, said Snell.

Among persistent infections, he said, there are two groups: those, like the man who was cured, who are relatively asymptomatic, and others who face more-serious outcomes.

Any long-term infection will affect the body, but even asymptomatic cases can prove dangerous: "We do know that some people, even after several months, if they have this persistent infection, can deteriorate at a later date."

And even though cases of chronic infection are rare, high levels of infection mean that vulnerable patients are more likely to be infected and potentially develop chronic infections, he added.

The aim of future research in this area is to collect enough data on persistent infections to identify new treatment options - an issue that has become all the more important given new variants' increasing resistance to antiviral treatments, Snell said.

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