500 days of COVID-19: Scientists discover world’s longest COVID infection

COVID infection
© iStock/OKrasyuk

UK researchers have discovered the world’s longest COVID infection, identifying a patient that carried the disease for a total of 505 days.

Performed by experts from King’s College London and Guy’s and St Thomas’ NHS Foundation Trust, the investigation found an individual who tested positive for COVID-19 for 505 days before their death, with the previous PCR confirmed COVID infection being 335 days.

The research included nine COVID patients in London, suggesting that COVID variants may present in immunocompromised individuals and found evidence of the first-ever occult COVID infection – where a patient appears to have cleared the virus and tests negative but is still found to have an ongoing infection.

Dr Luke Blagdon Snell, of Guy’s and St Thomas’ NHS Foundation Trust and the first author of the study, 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.”

Analysing the duration of COVID infection

The nine COVID patients, who were studied between March 2020 and December 2021, tested positive for the disease for at least eight weeks, with the average length of COVID infection being 73 days, although two participants had persistent infections for more than a year. All of the patients had compromised immune systems due to HIV, cancer, organ transplantation or medical therapies for other conditions.

The team performed regular sampling and genetic analysis of the virus, identifying that five of the nine patients developed at least one mutation that was a variant of concern (VOC). Specific individuals developed multiple mutations associated with VOCs, including the Alpha, Delta, and Omicron variants. Moreover, the COVID infection of one individual comprised ten mutations that would arise separately in VOCs, such as the Alpha, Gamma, and Omicron variants.

The researchers 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.

“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.”

First known occult infection

Of the patients studied, five survived, with two not requiring any treatment to get rid of their COVID infection. Two of the patients required antibody therapies and antivirals to clear the infection, and one has an ongoing infection.

At their last follow-up at the start of 2022, the person with the ongoing infection had been infected for 412 days and had been treated with monoclonal antibodies in an effort to alleviate the infection. If this person is still positive at their next follow-up check, they will have surpassed the 505 day COVID infection found in the study.

Dr Gaia Nebbia, a co-author of the research, commented: “Immunocompromised patients with persistent infection have poor outcomes, and new treatment strategies are urgently needed to clear their infection. This may also prevent the emergence of variants.”

The researchers also identified what may be the first occult infection of COVID-19.

The researchers concluded: “Occult infection describes someone who is thought to have cleared the virus, for instance, with negative tests but is later found to have an ongoing infection.

“This has been described with other viruses such as those that cause Ebola or hepatitis B and is different to long COVID, where the virus is generally thought to be cleared from the body, but symptoms persist.

“The patient was symptomatic and tested positive for COVID before recovering.  They then tested negative several times before developing COVID symptoms again several months later. A PCR test was positive, and genome sequencing of the virus at this point showed the infection was caused by the Alpha variant, which had by then been eliminated from the UK, suggesting the virus had been present in the body ever since the initial infection but remained undetected.”


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