Omicron and vaccines: An analysis on the decline in COVID-19 mortality

The SARS-CoV-2 virus emerged in December 2019 infecting more than 430 million people worldwide and causing almost 6 million deaths until February 2022. Rapid vaccination efforts during this period coincided with a reduction in the mortality rate of the virus. A new genetic COVID-19 variant named Omicron appeared and widely spread by the end of 2021, after which the COVID-19 mortality rate showed a marked, albeit temporary, decline. The potential relationship between vaccines and omicron infection on the mortality rate of COVID-19 is analyzed in this article using online data from public sources from countries with relatively high incidence of infection. Mortality and incidence rates were compared before and after Omicron became the prevalent source of COVID-19 cases, as well as the effect of vaccination during these periods. Infection rates were higher during Omicron than in the pre-Omicron period (4.16% vs. 2%, respectively), whereas mortality rates showed the opposite trend both in deaths over population (0.021% vs. 0.171%) and deaths over positive cases (0.27% vs. 1.07%, respectively). The results suggest that vaccines, while significantly reducing mortality, did not prevent Omicron infection; and that during the Omicron period mortality decreased by a low aggressiveness of this variant. Key Messages* Vaccines do not appear to have prevented Omicron infection. * Infection rates were higher during the Omicron period than before it. * Mortality rates were lower during the Omicron period than before it. * Vaccines reduced mortality rates during both pre- and Omicron periods. * The sharp decrease in mortality rates during the Omicron period seems to be due to the low virulence of Omicron strains rather than vaccine efficacy.