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Are recombination events at the origin of variants of concern?

Recombination is a transfer of genetic material between two nucleic acid molecules (DNA or RNA). With respect to viruses, it can occur during the replication of the viral genome when an individual is co-infected by 2 strains of the virus. This process may generate a new variant, carrying a part of the genome of the 1st strain, and a part of the genome of the 2nd strain. The most favourable conditions are when several variants circulate within a population, which usually happens in periods of high prevalence. British researchers (at the University of Edinburgh, Public Health Wales NHS Trust, Cardiff, and the University of Liverpool) have shown that recombination events occurred from the Alpha (⍺) or UK variant.

The researchers scanned data bases of UK SARS-CoV-2 sequences using bioinformatic analysis. The aim was to identify viral genomes made up partly of Alpha variant mutations and partly of mutations having characteristics of another variant, a sign of a possible recombination event. The suspect virus was then analysed with epidemiological and geographical data to determine whether a recombination event was really the cause of these variations.

In total, using a data base of 279 000 sequences up to March 2021, the researchers identified 16 candidates for a recombination event between an Alpha variant and another European strain in wide circulation in the UK during this period (for example, B.1.177). Those that were identified thankfully turned out not to be more pathogenic. The main risk in the emergence of a recombination variant would be if recombination took place between a highly transmissible variant, such as Alpha, and a highly pathogenic strain.

Monitoring these recombination events, where the viral strain acquires several mutations at the same time, is vital for quickly combatting the emergence of new, more dangerous variants. In any case, reducing the prevalence of SARS-CoV-2 by 2 (that is, the number of new infections) allows the risk of co-infection by 2 variants to be reduced by 4.

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