21 February 2024 , 16:30
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Persistent Covid infections are "surprisingly common" with those affected are more likely to report having Long Covid, a study by Oxford University has revealed.
The research, published in the journal Nature, states that about three in every 100 Covid infections last for a month or longer. They also suggest that these long-lasting infections can create new dangerous Covid variants. Many experts had already thought that versions of the virus such as Alpha and Omicron came from long-lasting infections in people with weaker immune systems.
But until this study, we didn't really know how many people get these persistent infections or what happens to the virus during them. The Oxford University researchers used information from the Office for National Statistics' (ONS) Covid Infection Survey. As part of the survey, people were tested about once a month.
From November 2020 to August 2022, over 90,000 people took part in the survey, out of which 3,603 people tested positive for the virus twice or more. 381 of these people tested positive for the same viral infection for a whole month or even longer.
Among this group, 54 people had an infection that lasted at least two months. The scientists reckon that between one in a thousand and one in 200 (0.1-0.5%) of all infections might stick around for at least 60 days. In some cases, people stayed infected with variants that had already disappeared from the general population.
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On the other hand, the researchers also found that catching the same variant again was very rare, probably because the person developed immunity to that variant and the variant reduced to very low levels after a few months. Out of the 381 long-lasting infections, 65 took three or more PCR tests during their infections.
Most of these individuals (82%) showed bouncing viral dynamics; experiencing high, then low, then high viral load dynamics - or how much of a virus remains in an infected person's blood. The researchers say this shows that the virus can hide in an infected individual while still being able to actively replicate during prolonged infections.
They also found that those with long-lasting infections were 55 per cent more likely to report having symptoms of Long Covid more than 12 weeks since the start of the infection compared with those with more typical infections. Some individuals showed a very high number of mutations, including mutations that define new coronavirus variants, alter target sites for monoclonal antibodies, and introduce changes to the coronavirus spike protein.
Most people didn't have lots of mutations, which means not every long-lasting infection could lead to new scary variants. Study co-lead author Dr Mahan Ghafari said: "Our observations highlight the continuing importance of community-based genomic surveillance both to monitor the emergence and spread of new variants, but also to gain a fundamental understanding of the natural history and evolution of novel pathogens and their clinical implications for patients."
Dr Katrina Lythgoe, another co-lead author from the Pandemic Sciences Institute, added: "Although the link between viral persistence and Long Covid may not be causal, these results suggest persistent infections could be contributing to the pathophysiology of Long Covid. Indeed, many other possible mechanisms have been suggested to contribute to Long Covid including inflammation, organ damage, and micro thrombosis."