Some people carry the coronavirus for a long time, as studies from Great Britain and the USA show.
Frankfurt – Some people have difficulty getting rid of the coronavirus and are infected for more than a month.
In some cases, the pathogen can still be detected in the blood and tissue after more than a year.
This is the result of studies by Oxford University (Great Britain) and the University of California in San Francisco.
The continued presence of Sars-CoV-2 in the body increases the risk of Long Covid and can potentially lead to the formation of new variants.
The proportion of persistent infections in the general population appears to be much higher than previously assumed.
For its study, the Oxford University research team used data from the “Office for National Statistics Covid Infection Survey”, where more than 90,000 women and men were tested for Sars-CoV-2 every month between November 2020 and August 2022.
In 3,603 people, two or more samples were positive during this period, and in 381 of them the same viral infection could be detected for a month or longer.
So they had not become infected again, but had not overcome their original infection.
Within this group, 54 men and women suffered from a particularly stubborn infection that lasted at least two months.
The researchers estimate that between one in 1,000 and one in 200 infections last at least 60 days.
Coronavirus can multiply in the body even after a long period of time
In some cases, participants were also infected with variants that were no longer circulating in the general population.
At the same time, the scientists found that repeated infection with the same variant was very rare, which they interpreted as an indication that immunity is building up against a variant.
In 65 of the 381 participants with infections lasting longer than two months, three or more PCR tests were carried out during this time.
Most of them showed a changing viral load, which was initially high, then fell and then rose again.
The study authors see this as evidence that the coronavirus is still able to multiply in the body even after a long period of time.
Some study participants had “extremely high” numbers of corona mutations
A persistent infection should not be confused with Long Covid, the long-term consequences of an infection.
However: The probability of suffering from typical Long Covid symptoms such as fatigue, shortness of breath and concentration problems more than twelve weeks after infection was increased by 55 percent among participants with stubborn infections compared to “normal” courses.
Katrina Lythgoe from the Department of Biology and Pandemic Sciences Institute at the University of Oxford said: “Although the association between viral persistence and Long Covid may not be causal, these results suggest that persistent infections may contribute to the pathophysiology of Long Covid.”
An “extremely high” number of mutations were also detected in samples from some participants with persistent infections - including those affecting the spike protein - which is targeted by the vaccination - and which can also affect the effectiveness of monoclonal antibodies.
Even if this only affected a minority of those who were persistently infected, study author Mahan Ghafari calls for continued monitoring of the Sars-CoV2 genome “in order to keep an eye on both the emergence and spread of new variants” and “a basic understanding of the “The natural development of new pathogens and their clinical impact on patients.”
How do new variants of Sars-CoV-2 arise?
There are several possible explanations for how new variants of Sars-CoV-2 arise.
There is a widespread belief that they form in patients whose immune systems only work to a limited extent and therefore cannot eliminate the virus.
Another theory is that increasing immunity in the population through vaccination and infections puts strong selection pressure on the virus and requires it to change in order to continue infecting people.
In the first of two studies from California, viruses were found in the blood and tissue of some patients more than a year after the acute illness;
Here too, the researchers interpret this as a potential cause of Long Covid.
To do this, they examined blood samples from 171 people.
Interesting: Study leader Michael Peluso from the School of Medicine at the University of California assumes that they all had “normal immune reactions”.
However, the probability of a long virus presence in the body was significantly higher in more severe acute cases than in normal cases.
In the second study, the research team looked at samples from the University of California Long Covid tissue bank donated by people with and without Long Covid.
The scientists discovered parts of viral genetic material in some samples up to two years after the acute infection - without there being any evidence that the person in question had been repeatedly infected.
The viral material was found in the connective tissue, where immune cells also abounded, which in turn suggests that the Sars-CoV-2 fragments kept the immune system on its toes.
In fact, the researchers discovered evidence in some samples that the virus could still be active.
According to Michael Peluso, further studies must now clarify whether virus fragments also promote Long Covid.
(pam)