Variants of Covid

These days we are hearing a lot about the Covid variants from the UK, South Africa or Brazil. Sometimes we also speak of strains and mutations. What is the difference?
Viruses are continually mutating, a mutation is a change in their RNA sequence. When a certain number of changes accumulate in the genome of a virus, or when these changes are qualitatively relevant, we can speak of a variant with respect to the original virus. And when the changes are so important that the functionality of the virus is substantially altered, for example giving it the ability to infect new cells, or make the vaccine obsolete, we are faced with a new strain. Consequently, the dreaded British variant, being a variant, produces an immune response analogous to the rest of the variants, and the vaccines developed so far are still effective in preventing it.
Nextstrain is an open source project to harness the scientific and public health potential of pathogen genome data. It enables real-time monitoring of pathogen evolution and offers a continuously updated visualization of publicly available data along with powerful analysis and visualization tools for community use. The goal is to aid epidemiological understanding and improve response to outbreaks.
For example, we can see the phylogenetic tree of Covid from its appearance to the present, how the different variants are distributed throughout the world, where the mutations are located in the virus genome, or how the different variants evolve by replacing each other.
Thus, we have a very illustrative example of pure Darwinism, the new variants have more infectious capacity and therefore displace the less efficient variants until they disappear, and one of the keys is the protein S of the viral coat.
Everything suggests that if the crown continues to mutate, the reign of the coronavirus will be perpetuated.