重症COVID–19におけるデルタ株流行の影響と予後：単施設後方視研究(Prognostic impact of delta variant in COVID–19 patients requiring mechanical ventilation in comparison with other variants: a single center retrospective analysis)

ABSTRACT Background : Spike protein mutations are known to affect the infectivity and virulence of coronavirus disease 2019 (COVID–19). The number of severe COVID–19 cases and deaths has increased due to the Delta variant. We aimed to evaluate the clinical characteristics and treatment outcomes of severe COVID–19 patients. Methods: Fifty–three consecutively presenting patients requiring mechanical ventilation for respiratory failure due to COVID–19 were seen at our institution between February 2020 and October 2021. We divided these patients into two groups: 13 patients admitted from July to October 2021 (the Delta period) and 40 patients admitted from February 2020 to June 2021 (the non–Delta period). We retrospectively compared overall survival between these groups (median observation period, 90 days). Results : All patients were unvaccinated. No L452R mutations were detected during the non–Delta period, whereas 10 (77%) such mutations were detected during the Delta period. Patient characteristics (non–Delta vs. Delta) were as follows: age, 68 vs. 56 years (P<0.01); body mass index, 27 vs. 30kg/m2 (P=0.02); P/F ratio (PaO2/FiO2), 136 vs. 80 (P<0.01); and days to hospitalization, 6 vs. 8 days (P=0.03). The 90–day survival rate was lower in the Delta group (71% vs. 37%, P<0.01). Multivariate analysis showed that the Delta variant was an independent unfavorable prognostic factor (hazard ratio 6.35, 95% confidence interval 1.96–20.6). Conclusion : Despite a younger patient age, survival rate was significantly worse in the Delta period. This is probably due to the infectivity and virulence of the Delta variant and delays in treatment caused by difficulty in transportation.