A new study by Oxford University researchers has shown that the proportion of ‘persistent’ infections with the pandemic coronavirus SARS-CoV-2 in the general population is higher than previously thought – ‘persistent’ is defined as infections that last a month or more more.
“Uncharted” persistent infections in the general population
Until now, it was thought that long-term COVID-19 infections mainly affecting people with weakened immune systems were the main “source” of the many and diverse new variants that appeared during the acute phase of the pandemic, causing continuous pandemic “waves” . However, until now, the incidence of persistent SARS-CoV-2 infections in the general population as well as how the virus evolves within the body of many has remained an uncharted landscape for scientists.
To ‘map’ this uncharted territory researchers from the University of Oxford used data from the UK’s Office for National Statistics on COVID-19 (ONS-CIS) – in this context it was tested almost monthly for COVID -19 to thousands of volunteers.
The… persistent results
Specifically, of the more than 90,000 participants tested, 3,603 tested positive for COVID-19 two or more times between November 2020 and August 2022 (the researchers also sequenced the viral genome in the samples).
According to the sequencing, 381 people (a rate of 10.5%) tested positive for the same infection for a period of one month or more. Of this group, 54 people had a persistent infection lasting at least two months.
The researchers estimated based on all the evidence that 1 in 1,000 to 1 in 200 (0.1%-0.5%) COVID infections can last at least 60 days.
Long infected with… extinct variants
In some cases, patients remained infected for a long time with variants of the virus that had now disappeared in the general population. However, the researchers saw that re-infection with the same variant was very rare, probably because the hosts developed immunity to the respective variant.
Many recurrent infections
Of the 381 cases of people with persistent infections, 65 underwent three or more molecular tests during their illness. Most of these people (82%) experienced recurrent infection – their viral load showed flares and dips. According to the researchers, this shows that the virus can retain the ability to multiply within the body for a long time in persistent infections.
Increased chances of long COVID
The study also found that people with persistent infection were 55% more likely to experience long-term COVID symptoms – symptoms that persisted for more than 12 weeks after the onset of infection – compared to people with a more “typical” disease picture.
Small number of mutations in most cases
Some patients carried a very large number of virus mutations in their bodies, including mutations that identified new variants of the coronavirus and were linked to mutations in the spike protein of the virus. However, most individuals did not carry a large number of mutations, suggesting that not all persistent infections are potential sources of new sources of virus variants of concern.
Dr Mahan Ghaffari, lead author of the study from the Institute of Pandemic Sciences at the University of Oxford’s School of Medicine noted that “our observations highlight the importance of continued genetic surveillance of the virus in the community both for
to monitor the emergence and spread of new variants as well as to gain basic knowledge about the evolution of new pathogens and the clinical impact they may have on patients”.
The association of persistent infection with long COVID
Dr. Katrina Lithgow from Oxford University’s Department of Biology and Department of Pandemic Sciences, another lead author of the study, emphasized that “although the link between persistent infection and long COVID has not been proven to be causal, the new findings suggest that the persistent infections may contribute to the pathophysiology of prolonged COVID. Of course, many other potential mechanisms have been suggested to contribute to long COVID including inflammation, organ damage and microthrombosis.”
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