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According to

Coronavirus has mutated at least once

The novel coronavirus that has infected thousands of people across the world may have mutated at least once — meaning there may be two different types of the virus causing illnesses, a new study conducted by Chinese scientists suggests.

Scientists with Peking University’s School of Life Sciences and the Institut Pasteur of Shanghai in a preliminary study found that one strain — type “L” — of the virus was more aggressive and accounted for about 70 percent of the strains analyzed. The second — type “S” — was less aggressive and accounted for about 30 percent of analyzed strains.

But also several webpages theorized the virus has mutated before passing from animals to humans.

This page What we know about the Wuhan virus says

This virus belongs to a family of viruses known as coronaviruses. Named for the crown-like spikes on their surfaces, they infect mostly bats, pigs and small mammals. But they mutate easily and can jump from animals to humans

and

Where did the new coronavirus come from? The new virus likely came originally from bats, scientists say. It isn’t known exactly where or how it jumped to humans, though. Viruses from bats often infect another mammal first and then mutate to become more transmissible to humans.

though

Coronaviruses can also jump directly to humans, without mutating or passing through an intermediate species.

Is something more known about this? Is it possible the virus has mutated twice in a period of time of months?

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    $\begingroup$ How many times has the virus mutated? As many times as it has replicated in a host. Viruses mutate every generation. Most of these mutations are "neutral" in the sense that they do not confer new evolutionary advantages or disadvantages. They likely do not even give a different phenotype. But they are mutations nonetheless. $\endgroup$
    – Cody Gray
    Commented Mar 11, 2020 at 0:32
  • $\begingroup$ This coronavirus is a RNA and tries to replicates lots of times with lots of bad replications. Is it any wonder that some successes are mutations? $\endgroup$
    – user2617804
    Commented Mar 11, 2020 at 8:49
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    $\begingroup$ Can we please start calling it Covid-19 instead of corona? Corona is a family. SARS, MERS, Covid, all coronas. Questions like this are going to be a pain with the next outbreak in a few years. $\endgroup$
    – Mast
    Commented Mar 11, 2020 at 14:20
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    $\begingroup$ @Mast If you want to be technical, the name of the virus is SARS-CoV-2; COVID-19 is the name of the disease caused by that virus. $\endgroup$
    – Charles
    Commented Mar 11, 2020 at 15:12
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    $\begingroup$ @Charles Fine with me, as long as we stop with the corona-this, corona-that. $\endgroup$
    – Mast
    Commented Mar 11, 2020 at 17:02

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This question makes a number of incorrect assumptions and I don't have time to correct them. The short answer is that the virus has mutated probably hundreds of times since it entered humans in late 2019.

The lower figure on the NextStrain.org ncov page, "Diversity", shows the known mutations that have been identified so far. As I look at it now, there are maybe 100-200 shown there, but that will change daily and I can't be bothered to count them.

Is it possible the virus has mutated twice in a period of time of months? Of course it is. That's what we expect from coronaviruses. It would be shocking if it did not.

The default assumption (based on a vast amount of experience with coronaviruses and many other viruses) is that these mutations are neutral and do not affect the virus in terms of fitness, virulence, or transmissibility in any way; they are occasionally useful in tracking sources, but unless you have spent a lot of time looking at virus phylogenetic trees for several years, your interpretations of these mutations are almost certainly wrong.

An example of people making claims based on unfamiliarity with virus evolution is the "two different types of the virus" claim. That claim is addressed by MacLean and colleagues in their Response to “On the origin and continuing evolution of SARS-CoV-2”. Summary:

Two of the key claims made by this paper appear to have been reached by misunderstanding and over-interpretation of the SARS-CoV-2 data, with an additional analysis suffering from methodological limitations

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    $\begingroup$ MacLean et al.'s "Response" to Tang et al.'s paper gives this stronger summary: "Given these flaws, we believe that Tang et al. should retract their paper, as the claims made in it are clearly unfounded and risk spreading dangerous misinformation at a crucial time in the outbreak." $\endgroup$
    – mgkrebbs
    Commented Mar 10, 2020 at 17:54
  • $\begingroup$ The default assumption as described here The default assumption (based on a vast amount of experience with coronaviruses and many other viruses) is that these mutations are neutral and do not affect the virus in terms of fitness, virulence, or transmissibility in any way has been proven wrong at least three times by SARS-CoV-2: The mutation D614G, the Alpha variant, and the Delta variant came with significantly improved fitness and show an ongoing adaption to the new human host of the virus. $\endgroup$
    – Sir Cornflakes
    Commented Oct 25, 2021 at 16:02
  • $\begingroup$ I don't think you understand what "default assumption" means. $\endgroup$
    – iayork
    Commented Oct 25, 2021 at 20:13
  • $\begingroup$ I added this as a caveat for the readers. And probably in the case of a zoonotic virus hitting mankind rather recently, this default assumption is profoundly wrong, as the virus is still in the process of adaption to its new host. At least, the huge increases in transmissibility have caught leading virologists such as C. Drosten as bad surprises. $\endgroup$
    – Sir Cornflakes
    Commented Oct 29, 2021 at 10:02

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