The pandemic has raged on for years now, and some people continue to bear the brunt of it far more than others: countries deprived of vaccines, essential workers keeping people safe and economies ticking, and immunocompromised people at greater risk of contracting COVID-19 having to shelter from the viral storm.

People with weakened immune systems from illness or medical treatments like chemotherapy are also more susceptible to developing infections lasting months, in which time the virus could develop new mutations.

The risk for all of us is that the longer it takes to stamp out the virus, the more time it gives new COVID-19 variants the chance to arise.

A team of researchers in the UK has now described a series of chronic COVID-19 infections, including a man who was infected for more than 400 days. He finally tested negative after genetic sequencing revealed which strain of the virus he had – and what treatment he needed.

Led by infectious disease physician Luke Blagdon Snell of Guy's and St Thomas' NHS Foundation Trust, the team has been investigating persistent infections in immunocompromised people, looking to understand which mutations occur and if new variants evolve over time.

Earlier this year, we learned of a person treated by the same team who tested positive for SARS-CoV-2 for 505 days before they died – the longest-known infection of COVID-19.

This latest case report describes a 59-year-old man who first contracted COVID-19 in December 2020. Genomic sequencing showed he carried an early strain of the virus that was widespread in the UK at the time.

"[W]hen 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," Blagdon Snell told the Washington Post.

These chronic coronavirus infections are distinct from long COVID, where an exasperating mix of symptoms persist long after the acute infections subsides for reasons that scientists are still grappling to understand.

Throughout the pandemic, we've used genomic sequencing to trace the origins of COVID-19 outbreaks, untangle intermixing lineages of the virus, and detect new variants.

In this report, Snell and colleagues describe how they use genomic sequencing results, delivered in 24 hours, to tailor treatments for people with persistent COVID-19 infections, and finally rid their bodies of the virus.

The paper describes six cases, the 59-year-old man among them.

With a weakened immune system following a kidney transplant, the man's body couldn't clear the virus and with only mild and intermittent symptoms, he wasn't eligible for treatments used to prevent or treat severe cases of COVID-19.

He tested positive in February 2021 and again in January 2022, each time with the same variant of the virus: B.1.177.18. Over time, a collection of mutations cropped up in the virus at a rate expected with SARS-CoV-2 – so nothing out of the ordinary there, only that it underscores the propensity of the virus to shapeshift.

While researchers think these cases of chronic infection are rare, they are difficult to treat since the continual emergence of new variants has rendered neutralizing antibody therapies ineffective.

Once the researchers knew the man had a chronic infection, he received a combination monoclonal antibody treatment effective against early strains, which finally rid him of the virus, 411 days after he was first diagnosed.

Other cases described by Snell and colleagues include cases where genomic sequencing revealed which strains of SARS-CoV-2 people had, if it was a separate or chronic infection, and what mutations the virus had acquired – allowing physicians to select the right therapy.

The care teams are still closely monitoring a few patients through their recovery. Omicron subvariants pose a new threat, however, as some strains thwart all available antibody treatments.

"Some people with weakened immune systems are still at risk of severe illness and becoming persistently infected. We are still working to understand the best way to protect and treat them," Snell says.

At least where genomic sequencing facilities are available, this research shows that the virus cannot – and should not – evade our watch indefinitely. Lives depend on it.

The report was published in Clinical Infectious Diseases.