British researchers announced on Friday they have cured a man who had been infected with Covid continuously for 411 days by analyzing the genetic code of his particular virus to find the right treatment.

Persistent Covid infection – which is different from long Covid or repeated bouts of the disease – occurs in a small number of patients with already compromised immune systems.

These patients can test positive for months or even years, with the infection “rolling around all the time,” said Luke Snell, an infectious disease doctor at Guy’s and St Thomas NHS Foundation Trust.

The infections can pose a serious threat as around half of patients also have persistent symptoms such as pneumonia, Snell told AFP, adding that much is still unknown about the condition.

In a new study published in the journal Clinical Infectious Diseases, a team of researchers from Guy’s and St Thomas NHS Foundation Trust and King’s College London describe how a 59-year-old man finally got over his infection after more than 13 months .

The man, who has a compromised immune system following a kidney transplant, contracted Covid in December 2020 and continued to test positive through January this year.

To find out if he had contracted Covid multiple times or if it was an ongoing infection, the researchers used rapid genetic analysis using nanopore sequencing technology.

The test, which can provide results in as little as 24 hours, showed the male had an early B.1 variant that was dominant in late 2020 but has since been replaced by newer strains.

Because he had this early variant, the researchers gave him a combination of Regeneron’s monoclonal antibodies casirivimab and imdevimab.

Like most other antibody treatments, the treatment is no longer widely used because it is ineffective against newer variants such as Omicron.

But it successfully cured the man because he was fighting a variant from an earlier phase of the pandemic.

“The very new variants that are becoming more common now are resistant to all the antibodies that are available in the UK, the EU and now even the US,” Snell said.

Researchers tried several such treatments in August this year to save a critically ill 60-year-old man who had been infected since April.

“We really thought he was going to die,” Snell said.

So the team chopped up two antiviral treatments that hadn’t previously been used together — paxlovid and remdesivir — and administered them to the unconscious patient via a nasogastric tube, according to a non-peer-reviewed preprint study on website ResearchSquare.

“Miraculously, he was cured and perhaps now this is how we treat these very difficult ongoing infections,” Snell said, stressing that this treatment may not apply to normal Covid cases.

At the ECCMID conference in April, the team announced the longest-known persistent infection in a man who tested positive 505 days before his death.

This “very sad case” occurred earlier in the pandemic, Snell said, adding he was grateful that so many more treatment options were now available.