Differences in incidence and fatality of COVID-19 by SARS-CoV-2 Omicron variant versus Delta variant in relation to vaccine coverage: A world-wide review

Abstract

We aim to evaluate the evolution differences in the incidence and case fatality rate (CFR) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta and Omicron variants. The average incidence and CFRs were described between different countries. A gamma generalized linear mixed model (GLMM) was used to compare the CFRs of Delta and Omicron variants based on vaccination coverage. Totally, 50 countries were included for analyses. The incidence of coronavirus disease 2019 (COVID-19) ranged from 0.16/100,000 to 82.95/100,000 during the Delta period and 0.03/100,000 to 440.88/100,000 during the Omicron period. The median CFRs were 8.56 (interquartile range [IQR]: 4.76-18.39) during the Delta period and 3.04 (IQR: 1.87-7.48) during the Omicron period, respectively. A total of 47 out of 50 countries showed decreased CFRs of the Omicron variant with the rate ratio ranging from 0.02 (95% confidence interval [CI]: 0.01-0.03) (in Cambodia) to 0.97 (95% CI: 0.87-1.08) (in Ireland). Gamma GLMM analysis showed that the decreased CFR was largely a result of the decreased pathogenicity of Omicron besides the increased vaccination coverage. The Omicron variant shows a higher incidence but a lower CFR around the world as a whole, which is mainly a result of the decreased pathogenicity by SARS-CoV-2's mutation, while the vaccination against SARS-CoV-2 still acts as a valuable measure in preventing people from death.

Keywords: SARS-CoV-2 Delta; SARS-CoV-2 Omicron; case fatality rate.

Figure 1

The flow chart of the recruitment of countries for analysis

Figure 2

The time interval of Delta and Omicron periods that were extracted for data analysis. (A) The Delta period among 50 recruited countries. (B) The Omicron period among 50 recruited countries.

Figure 3

The incidences, case fatality rates, and rate ratios between Delta and Omicron periods among the 50 countries distributed around the world. (A) The incidences and case fatality rates during the Delta period among the 50 countries distributed around the world. (B) The incidences and case fatality rates during the Omicron period among the 50 countries distributed around the world. (C) Rate ratios of the incidences between Delta and Omicron periods among the 50 countries distributed around the world. (D) Rate ratios of the case fatality rates (CFRs) between Delta and Omicron periods among the 50 countries distributed around the world.

Figure 4

The forest plot of the pooled analysis on rate ratios of the incidences and case fatality rates between Delta and Omicron periods categorized by population size, gross domestic product (GDP) per capita, vaccination coverages, and area. (A) The pooled‐analysis on rate ratios of the incidences and case fatality categorized by population size. (B) The pooled‐analysis on rate ratios of the incidences and case fatality categorized by GDP per capita. (C) The pooled‐analysis on rate ratios of the incidences and case fatality categorized by vaccination coverages. (D) The pooled‐analysis on rate ratios of the incidences and case fatality categorized by area.

Figure 5

Impacts of vaccination on the incidence and case fatality between Delta and Omicron periods among the 50 countries. (A) Impacts of partial vaccination coverages on the incidence and case fatality between Delta and Omicron periods. (B) Impacts of fully vaccination coverages on the incidence and case fatality between Delta and Omicron periods. (C) Impacts of booster vaccination coverages on the incidence and case fatality between Delta and Omicron periods.