Intra-Host Mutation Rate of Acute SARS-CoV-2 Infection During the Initial Pandemic Wave

Background Our understanding of SARS-CoV-2 evolution and mutation rate is limited. The rate of SARS-CoV-2 evolution is minimized through a proofreading function encoded by NSP-14 and may be affected by patient comorbidity. Current understanding of SARS-CoV-2 mutational rate is through population based analysis while intra-host mutation rate remains poorly studied. Methods Viral genome analysis was performed between paired samples and mutations quantified at allele frequencies (AF) ≥0.25, ≥0.5 and ≥0.75. Mutation rate was determined employing F81 and JC69 evolution models and compared between isolates with (ΔNSP-14) and without (wtNSP-14) non-synonymous mutations in NSP-14 and by patient comorbidity. Results Forty paired samples with median interval of 13 days [IQR 8.5-20] were analyzed. The estimated mutation rate by F81 modeling was 93.6 (95%CI:90.8-96.4], 40.7 (95%CI:38.9-42.6) and 34.7 (95%CI:33.0-36.4) substitutions/genome/year at AF ≥0.25, ≥0.5, ≥0.75 respectively. Mutation rate in ΔNSP-14 were significantly elevated at AF>0.25 vs wtNSP-14. Patients with immune comorbidities had higher mutation rate at all allele frequencies. Discussion Intra-host SARS-CoV-2 mutation rates are substantially higher than those reported through population analysis. Virus strains with altered NSP-14 have accelerated mutation rate at low AF. Immunosuppressed patients have elevated mutation rate at all AF. Understanding intra-host virus evolution will aid in current and future pandemic modeling. ### Competing Interest Statement The authors have declared no competing interest.