The SARS-CoV-2 viruses have been categorized into two major types, with L being the
major type (~70%) and S being the minor type (~30%).The S type is actually the ancestral version of SARS-CoV-2. Evidences are suggesting that the L type might be more aggressive than the S type due to the potentially higher transmission and/or replication rates. It has been hypothesized that the two types of SARS-CoV-2 viruses might have experienced different selective pressures due to different epidemiological features.. This explains why initial reports from Wuhan described a higher mortality than some more recent case series.