During the first year of the Coronavirus pandemic, a relatively slow but constant rate of viral mutations occurred. However, since the end of 2020, several variants characterized by a large number of mutations have emerged, exceeding by far the mutation rates observed in the first stage of the pandemic.
A new study led by Tel Aviv University has found that immunocompromised patients tend to develop chronic Coronavirus infections, allowing the virus to accumulate a variety of mutations, which can make it become more transmissible and able to evade prior natural or vaccine-induced immunity, as was the case of the Omicron variant.
The scientists argue that weakened antibody responses – particularly in the lower airways of chronic patients – may prevent their full recovery and drive the Coronavirus to mutate several times during lengthy infections, potentially leading to the emergence of new variants.
“The Coronavirus is characterized by the fact that in every population, there are people who become chronically infected. In the case of these patients, the virus remains in their body for a lengthy period of time, and they are at high risk for recurrent infection,” explained study senior author Adi Stern, an expert in viral evolution at the Tel Aviv University.
“In all of the cases observed so far, these were immunocompromised patients – part of their immune system is damaged and unable to function. In biological evolutionary terms, these patients constitute an ‘incubator’ for viruses and mutations – the virus persists in their body for a long time and succeeds in adapting to the immune system, by accumulating various mutations.”
By examining 27 chronic Covid-19 patients at the Tel Aviv Sourasky Medical Center, Professor Stern and his colleagues found that their weakened immune systems have often created pressure for the virus to mutate. Most of these patients showed a pattern of apparent recovery, followed by recurring viral infection.
The analysis revealed that, when such a pattern of apparent recovery was observed – based on negative nasopharyngeal swabs – the virus continued to thrive in the patients’ lungs, where it accumulated several mutations before travelling back to the upper respiratory tract.
“The complexity of Coronavirus evolution is still being revealed, and this poses many challenges to the scientific community. I believe that our research has succeeded in peeling back a missing layer of the big picture, and has opened the door for further research efforts to discover the origins of the various variants. This study highlights the importance of protecting immunocompromised individuals, who are at high risk for the virus, yet may also be an incubator for the formation of the next variant, posing a risk to all of us,” Professor Stern concluded.
The study is published in the journal Nature Medicine.
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