Thank you for your question and I'm honored to have an ER doctor here :)

First, a July paper says, "Our analysis of 48,635 SARS-CoV-2 highlights a total of 353,341 mutation events compared to the NC_045512.2 Wuhan reference genome. " (source: https://www.frontiersin.org/articles/10.3389/fmicb.2020.01800/full)

While mutations can always happen, they don't necessarily give rise to a new strain (i.e., a variant with distinct biological properties). Mutations may result in variants with same biological properties (not qualified as different strains).

As far as I know, only one study (source: https://www.cell.com/cell/fulltext/S0092-8674(20)30877-1?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867420308771%3Fshowall%3Dtrue#secsectitle0055) has examined the biological properties of SARS-CoV-2 variants. You can see the number of variants with distinct biological properties in the table 1 of this study.

As the study authors wrote, "As shown in Figure 1, group A represents all high-frequency variants and combined variants with D614G across the entire S gene (29 strains) excluding receptor-binding domain (RBD) region. Group B includes variants in RBD (51 strains). "

At the same time, the study emphasized that most strains are not very infective, and that the D614G is the most successful in spreading itself globally.

Let me know if you have anything else to ask or add :))