Monitoring the Status of Multi-Wave Omicron Variant Outbreaks - 71 Countries, 2021-2023.

What is already known about this topic?: Analyzing the characteristics of epidemic development after the emergence of the severe acute respiratory syndrome virus 2 Omicron variants with its subvariants and the impact of income level inequalities on the coronavirus disease 2019 (COVID-19) case-fatality ratio helps to better understand the spread of novel coronavirus infections.

What is added by this report?: The median time interval between the first and second waves of Omicron sub-variants was 70 days (interquartile spacing: 43.75-91), and between the second and third waves was 87.5 days (interquartile spacing: 49-119), which obeyed a lognormal distribution. The case-fatality ratio of the first wave was significantly higher than that of the second and third waves. During the initial epidemic period, there was no significant geographic differences in the case-fatality ratio of the first wave, while the case-fatality ratio in countries with high income levels was significantly lower than in countries with other income levels.

What are the implications for public health practice?: We still need to pay attention to the COVID-19 pandemic, as inequalities in income levels have an impact on the case-fatality ratio during the early stages of Omicron epidemics. In most countries, strains of the virus are likely to move from low to high population prevalence after 2-4 months.