A UK patient had a sustained Covid-19 infection for more than a year in what may be the longest known case of the disease, according to a new study.

       The patient had a severely weakened immune system, researchers said, adding that their study proved the need for continued precautions to protect vulnerable people, especially as many countries — including the UK itself — ease Covid restrictions.

       Dr Luke Blagdon Snell, an infectious disease expert at the Guy’s & St Thomas’ NHS Foundation Trust, said that at 505 days, this “certainly seems to be the longest reported infection”, though it cannot be stated for certain because not all cases are reported or tested consistently as in this case.

       Before this, researchers had believed that the longest-lasting Covid infection was for 335 days.

       Dr Snell’s team conducted the study on nine patients who tested positive for Covid for at least eight weeks. Five of those patients survived, but the person who had Covid for 505 days has died.

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       All patients involved in the study had weakened immune systems due to a host of reasons, including organ transplants, HIV, cancer or treatment from other illnesses.

       Repeated tests conducted on the nine patients showed that their infections continued for an average of 73 days. Two patients had Covid for more than a year.

       Through repeated testing, researchers analysed the genetic code of the virus to determine whether it was the same strain or not and to see if patients got Covid more than once.

       Researchers said the genetic sequencing showed that the virus changed over time and mutated.

       Dr Snell added that the mutations were similar to those that later showed up in widespread variants.

       “This provides evidence that mutations found in variants of concern do arise in immunocompromised patients and so supports the idea that new variants of the viruses may develop in immunocompromised individuals,” Dr Snell said in a press release.

       “It is important to note, however, that none of the individuals in our work developed new variants that became widespread variants of concern.

       “Additionally, whilst this work shows variants could arise in immunocompromised individuals, whether the previous variants of concern like Alpha, Delta and Omicron arose in this manner remains unknown.”

       Scientists said that the research shows the need for continued precautions as countries lift Covid norms.

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       “Masking in crowds is a considerate thing to do and a way we can protect others,” said Dr Wesley Long, a pathologist at Houston Methodist in Texas, who was not part of the research.

       Additional reporting by agencies