Genetic analysis by Chinese scientists of 103 samples of the virus, taken from patients in Wuhan and other cities, suggests that early on two main strains emerged, designated L and S. Although the L strain appeared to be more prevalent than the S strain (about 70% of the samples belonged to the former), the S branch of the virus was found to be the ancestral version. The team behind this research suggested that this may indicate the L strain is more “aggressive”, either transmitting more easily or replicating faster inside the body. However, this theory is speculative at this stage – there haven’t yet been direct comparisons to see whether people who catch one version of the virus are more likely to pass it on or suffer more severe symptoms.