The original coronavirus strain has almost disappeared in the US. One chart shows how variants took over.

Coronavirus variants have mostly replaced the original strain, making it virtually obsolete.In April, the dominant strain in the US was taken over by the Alpha variant. It could be replaced by Delta soon.Scientists don't know if more contagious variants of the dominant species will emerge.Subscribe to the Insider Healthcare Newsletter for the most recent healthcare news and analysis sent straight to your inbox Loading Click Sign up to receive marketing emails and other offers from Insider.Viruses will do whatever it takes to survive, even if that means replacing an older, weaker virus with one more transmissible.For the first few months of the pandemic the coronavirus was not more dangerous. Each new infected person passed it on to two to three people an average. Scientists believed that the original virus strain, also known as the "wild type," had already been sufficiently contagious that it would not spread further.As the pandemic spread and more people were infected, the coronavirus was able to reproduce and mutate more, causing small and random changes in its genetic sequence. While most mutations are harmless, there are rare instances when a distinct set of genes yields new properties.Scientists believe that variants of the original strain have nearly completely replaced it in the US. This renders it virtually obsolete.Insider was told by Tyler Starr, a postdoctoral researcher at Fred Hutchinson Cancer Research Center. "Pretty much every virus currently in circulation has one of these variants."Below is a chart that shows how just a few strains have been dominant in the US since February. There are more than 200 other strains of the virus that are less common, as well as the original.The Alpha variant was first discovered in the UK in September. It became widespread in the US between February and April. It accounted for 27% to 70% respectively of all circulating strains. According to the Centers for Disease Control and Prevention, it's approximately 50% more transmissible that the original strain. The share of coronavirus strains, including the original, fell to 4% from 20%.Alpha was already up against Delta by May. Public Health England's analysis found that Delta was associated with a 60% higher risk of household transmission than Alpha. However, more recent estimates indicate that this difference may be closer to 40%.Delta rose from less than 3 percent of all US circulating strains to over 20% between May and June. Within weeks, it could be the dominant strain in the US.Starr stated that Delta overtakes Alpha variants almost everywhere once it reaches there. This is proof that it is transmissible to a certain degree."Is there a more contagious version of Delta that could replace it?On April 15, 2021, researchers sequenced coronavirus samples at University Hospital of Badajoz in Spain. Javier Pulpo/Europa Press/Getty ImagesStarr stated that coronavirus variants, including Delta, have not shown any significant differences from the wild type.He said that mutations could modify transmissibility, but that the trait was already present in the original virus. It's only being modified slightly.Scientists are beginning to wonder if the virus has reached "peak fitness", the point at which it stops mutating and becomes more infectious.According to the World Health Organization, Delta is the most "fittest" strain to date. It is more transmissible than any other strains and may be even deadlier. Researchers from Scotland discovered that Delta infection doubled the likelihood of being admitted to hospital compared to Alpha. Previous studies suggest that the Alpha variant could be 30% to 70% more deadly than the original strain. Vaccines are able to significantly reduce the risk for both variants."Delta is definitely going up the fitness peak, whether it's at top, I think that’s very difficult to say until we just see no further change," Andrew Read, a researcher at Pennsylvania State University who studies the evolution infectious diseases, told Insider recently.He said, "If Delta takes control of the world and everything changes," adding that "then we will know in a year or so that it is the most suitable."Starr believes that the virus will continue to evolve.He said that the virus would continue to evolve and be capable of transmitting and infecting people as long as people have immunity. "But, at the same moment, we'll also have that low-level immune response that makes it a less severe thing over the long term."There is still the possibility that a new lineage could replace Delta as dominant. Or that two versions of Delta and Alpha could merge mutations to create an even more dangerous strain. The virus could become a "variant with high consequences" that is more distinct than current variants and resistant to vaccines. This has not been confirmed.