SARS-CoV-2 displays very little sequence diversity due to having a proofreading mechanism, yet there are still chances for natural selection to occur in its favor
[31][32][33]. The more SARS-CoV-2 pandemic remains in the population, the greater its possibility to gather immunologically associated mutations, even after the vaccine is available
[34][35][36][37][38]. Scientists are solely focused on understanding the evolutionary mechanisms of SARS-CoV-2, including mutation, recombination, and tracing for indels in the genome as they were found in previously discovered coronaviruses
[39]. Experiments with the evidence of antigenic drift were seen in previous strains, such as OC43, 229E, and SARS CoV-1, but have not yet been found in SARS-CoV-2
[34][35][36][37][38][40][41]. In 2003/2004 viruses, the point mutation D480A/G on the receptor binding domain (RBD) spread with an impactful prevalence in humans and civet cats. In vitro, recapitulated elevation of D480A/G was induced due to immune pressure by neutralizing antibody 80R
[42]. Likewise, point mutations were detected to be worthwhile as an inhibitor for neutralizing antibodies in SARS-CoV-1 and MERS-CoV
[42][43]. An evolutionary analysis on 351 sequences found two mutations in nsp6 and near the ORF10 region in earlier COVID-19 strains may confer less stability to protein structures. Notably, the nsp6 creates autophagosomes and is available in the endoplasmic reticulum (ER) of both alpha and beta coronaviruses. Accordingly, the mutation in nsp6 may confer a noteworthy change in the expression of SARS-CoV to its host, especially in the autophagic lysosomal system
[44]. In SARS-CoV-2, another significant amino acid change, D614G, has been traced to appear recurrently in the spike protein worldwide. Before the G614 variant, the original D614 form was firmly retained. An A-to-G mutation gave rise to D614G substitution in the Wuhan reference strain at positions 23,403
[45]. In early March of 2019, G614 was infrequent worldwide, but gradually thriving in Europe. Eventually, variants carrying the D614G substitution were designated as “G clade”. Three additional mutations are also found to be present concurrently with the D614G variant, namely: (1) a C-to-T mutation at position 241, according to Wuhan reference sequence in the 5′ UTR, (2) a C-to-T silent mutation at position 3037, and (3) a C-to-T mutation at position 14,408 (RdRp P323L). Currently, the haplotype containing these four interlinked mutations is starting to be found frequently in Europe, continuing to North America, Oceania, and finally Asia. A study found evidence of higher titers (elevated 2.6–9.3 times) for the G614 variant in infected patients’ samples with lower Ct (cycle threshold) value in vivo, indicating higher viral load; yet, this does not confirm disease severity
[46]. However, G614 may induce spike stability and membrane fusion
[47].