1、 https:/crsreports.congress.gov Updated October 29, 2021COVID-19 Variants: Vaccines, Diagnostics, and TherapeuticsIntroduction As SARS-CoV-2, the virus that causes COVID-19, has spread widely over time, a number of new variants have been identified globally. According to the Centers for Disease Cont
2、rol and Prevention (CDC), “a new virus variant has one or more mutations that differentiate it from the wild-type or predominant virus variants already circulating among the general population.” Genetic variation in circulating viruses is expected, especially with RNA viruses like SARS-CoV-2, which
3、have high rates of mutation generally. When a virus infects its host, it uses the host cell machinery to replicate itself. This replication process is error prone and offers chances to introduce changes to the viruss genetic code. Many of these changes are inconsequential, but a few improve the fitn
4、ess of the virus, providing a selective advantage and establishing new strains of the virus, which would be expected to increase in prevalence over time. Although they may occur in any part of the viral genome, changes in the genetic code for the virus part that locks onto the host cell, known as th
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