Longest known Covid infection lasted more than 16 months, study finds

The longest known Covid infection is believed to have lasted for more than 16 months, or 505 days, researchers have said.

The unnamed patient, who had several underlying conditions, first started showing symptoms and tested positive in early 2020, and tested positive many times until dying in 2021.

Most people clear the virus naturally, but the patient had a severely weakened immune system.

The previous longest known infection is thought to have lasted 335 days.

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The researchers, from King’s College London and Guy’s and St Thomas’ NHS Foundation Trust, studied nine immunocompromised patients who tested positive for the virus for at least eight weeks.

They also presented evidence that new variants may arise in immunocompromised individuals.

Presenting their findings at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Lisbon, Portugal, they describe details of one of the first occult Covid infections – cases where the patient was thought to have cleared the virus with a negative test but is subsequently found to have had an ongoing infection.

The team were interested in how the virus changes over time in immunocompromised individuals.

First author Dr Luke Blagdon Snell, of Guy’s and St Thomas’ NHS Foundation Trust, said: “New variants of SARS-CoV-2, the virus that causes Covid-19, have emerged throughout the pandemic.

“Some of these variants transmit more easily between people, cause more severe disease, or make the vaccines less effective.

“One theory is that these viral variants evolve in individuals whose immune systems are weakened from illness or medical treatments like chemotherapy, who can have persistent infection with SARS-CoV-2.

“We wanted to investigate which mutations arise, and if variants evolve, in these people with persistent infection.”

In the nine patients included in the study, infections lasted for 73 days on average, but two patients had persistent infections for more than a year.

The patients, who were studied between March 2020 and December 2021, all had weakened immune systems due to organ transplantation, HIV, cancer, or medical therapies for other illnesses.

Five of the nine developed at least one mutation seen in variants of concern, analysis showed.

Some of the people developed multiple mutations associated with variants of concern, such as Alpha, Delta and Omicron.

The researchers found that the virus from one patient contained 10 mutations that would arise separately in variants of concern, such as Alpha, Gamma and Omicron.

Dr Snell and colleagues said: “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.

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

He added it was unknown whether previous variants of concern like Alpha, Delta and Omicron also arose in this manner.

Five of the nine patients studied survived, and one still has an infection - at their last follow-up in early 2022, that patient had been infected for 412 days.

The person has been treated with monoclonal antibodies, but if they still test positive at their next appointment, researchers suggest they will likely pass the longest known infection of 505 days as described in the new study.