"Population genetic analyses of 103 SARS-CoV-2 genomes indicated that these viruses evolved into two major types (designated L and S), that are well defined by two different SNPs that show nearly complete linkage across the viral strains sequenced to date. Although the L type (∼70%) is more prevalent than the S type (∼30%), the S type was found to be the ancestral version"
Сама саттья в формате ПДФ тут.
Basically the Less virulent S strain multiplies slower, so it takes people longer to become infectious and they shed less virus, but the milder illness means they are more likely to travel or work.
The More Virulent L strain replicates faster, so your get more severe disease in a wider age group, shed virus early on when you are asymptomatic, but symptoms are more pronounced allowing for quarantine intervention.
Здесь наглядно распространения ковариантов и прочие детали.
Любопытно, что, вероятнее всего, первый американский пациент, которого лечили и вылечили в шт. Вашингтон, за время своего короткого пребывания в Пекине (который не ьыл карантинным, и имел что-то оуоло 2 случаев на город), подхватил оба (!) штамма коронавирсуа:
"The viruses isolated from a patient that lived in the United States (USA_2020/01/21.a, GISAID ID: EPI_ISL_404253) had the genotype Y (C or T) at both 8,782 and 28,144. The most likely explanation is that this patient was infected by both the L and S types. Note the reference is L type"
Толковая интерпертация данных статьи с реддита
"They found 2 strains of SARS-COV-2, the L type and S type. From the samples collected in Wuhan early January, there were up to 97% ish infected with L-type and only 3% ish infected with S-type. They traced back the similarity of L-type and S-type structure to other bat viruses (predecessor viruses) and found out that S-type actually has more similarity to them, while L-type is more specific and mostly only similar to S-type. It could indicate that L-type is actually the mutated version of S-type, and thus more agressive.
Samples from outside Wuhan show only 70% ish infected by L-type and 30% ish infected by S-type. The lower number of L-type outside Wuhan might suggest the draconian measure China implemented on Wuhan actually work, with severe cases caused by L-type infection being tracked and isolated earlier so it decreases the rate of infection, while milder cases caused by S-type (possibly carried by travellers internationally) are roaming around more free because they more likely spread undetected.
There are also 2 cases that show you could be infected by both strains. The case in America (someone from Wuhan) and the case in Australia (also someone from Wuhan), both had been proven to be infected by L and S types. It's still inconclusive that this is the norm however since there are no more case studies on that.
I think it explains how in some people they only show mild symptoms while in others more severe, or even become fatal overnight. Take Iran as example, they probably have more L-type than S-type, while South Korea probably has more S-type than L-type."
Есть шансы, что линии могут разойтись и дальше, а так же,, ввиду уже приличного охвата члоевеческой популяции, на появление других вариантов, еще более приспособленных к заражению людей.