Three types of the deadly coronavirus are spreading around the world - and the US is being rocked by the original strain from China.
Cambridge University researchers mapped the genetic history of the infection from December to March and found three distinct, but closely related variants.
Analysis of the strains showed type A - the original virus that jumped to humans from bats via pangolins - was not China's most common. Instead, the pandemic's ground-zero was mainly hit by type B, which was in circulation as far back as Christmas Eve.
Results showed type A was the most prevalent in Australia and the US, which has recorded more than 400,000 COVID-19 cases. Two-thirds of American samples were of type A, but the infected patients mostly came from the West Coast, and not New York.
Dr Peter Forster and team found the UK was mostly being bombarded with type B cases, with three quarters of samples testing as that strain. Switzerland, Germany, France, Belgium and the Netherlands were also dominated by type B.
Another distinct variation, type C, descended from type B and spread to Europe via Singapore.
Scientists believe the virus, officially called SARS-CoV-2 is constantly mutating to overcome immune system resistance in different populations.
At least eight strains of the virus are being tracked by researchers around the world, using genetic detective work to show how the virus spreads.
The virus appears to mutate very slowly, with only tiny differences between the different strains and that none of the strains of the virus are more deadly than another, experts say.
They also added it does not appear the strains will grow more lethal as they evolve.
Scientists also said that despite conspiracy theories falsely claiming the virus was made in a lab, the virus's genome shows it began in bats.
According to figures updated last night, coronavirus had infected 1.5 million people worldwide and killed nearly 88,000 people.