Scientists from Emory University found the coronavirus variants of concern are emerging from chronic, long-term COVID infections in people who may be immune comprised and unable to clear the virus.
They found that the variants of concern come from rare cases when someone may have an active infection for months.
Viruses like SARS-CoV-2 continuously evolve due to occasional mutations in the genetic code that may occur when they replicate.
Usually, such random mutations do not benefit the virus or raise the concerns of scientists monitoring these changes.
Occasionally, however, the mutations result in a variant of the virus that may make it more transmissible, more difficult to detect and treat, and even more lethal.
The World Health Organization defines a SARS-CoV-2 variant of concern as one that is more likely to cause infections even in those who are vaccinated or in those who were previously infected.
In the study, the team built a mechanistic, theoretical model to study the problem, using existing data and software they developed.
The resulting model rules out the theory that the variants emerged from sustained transmission of acute infections and fully supports the theory that each variant evolved within a single individual with a chronic infection.
The model shows how multiple mutations were needed, each of which may have been either neutral or slightly advantageous to viral fitness.
In this way, a variant eventually acquires a constellation of mutations that allow it to become more transmissible.
The team says although the current paper drew from data for the alpha, beta and gamma variants, the resulting theoretical model also explains the later independent emergence of the delta and omicron variants.
The researchers have made their model and software publicly available for others to study the evolution of COVID-19 variants.
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The research was published in Frontiers in Virology and conducted by Daniel Weissman et al.
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