But are the mutations stable? and what causes them?
Quality control isn't perfect...
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The novel coronavirus which is responsible for the emerging COVID-19 pandemic mutates at an average of about two mutations per month.
General Concepts
Genetic Change in Viruses
Viruses are continuously changing as a result of genetic selection. They undergo subtle genetic changes through mutation and major genetic changes through recombination. Mutation occurs when an error is incorporated in the viral genome. Recombination occurs when coinfecting viruses exchange genetic information, creating a novel virus.
Mutations
Mutation Rates and Outcomes
The mutation rates of DNA viruses approximate those of eukaryotic cells, yielding in theory one mutant virus in several hundred to many thousand genome copies. RNA viruses have much higher mutation rates, perhaps one mutation per virus genome copy. Mutations can be deleterious, neutral, or occasionally favorable. Only mutations that do not interfere with essential virus functions can persist in a virus population.
Phenotypic Variation by Mutations
Mutations can produce viruses with new antigenic determinants. The appearance of an antigenically novel virus through mutation is called antigenic drift. Antigenically altered viruses may be able to cause disease in previously resistant or immune hosts.
Vaccine Strains from Mutations
Mutations can produce viruses with a reduced pathogenicity, altered host range, or altered target cell specificity but with intact antigenicity. Such viruses can sometimes be used as vaccine strains.
Recombination
Recombination involves the exchange of genetic material between two related viruses during coinfection of a host cell.