No abstract

What is already known about this topic? The first nationwide wave of coronavirus disease 2019 (COVID-19), driven by the Omicron variant, has largely subsided. However, subsequent epidemic waves are inevitable due to waning immunity and the ongoing evolution of the severe acute respiratory syndrome coronavirus 2. What is added by this report? Insights gleaned from other nations offer guidance regarding the timing and scale of potential subsequent waves of COVID-19 in China. What are the implications for public health practice? Understanding the timing and magnitude of subsequent waves of COVID-19 in China is crucial for forecasting and mitigating the spread of the infection.

Because of the fading immunity to COVID-19 and continuous evolution of the SARS-CoV-2 Omicron variants, the next epidemic wave of COVID-19 is inevitable. The Omicron variant has been the cause of several waves of the COVID-19 epidemics in the majority of countries. Thus, lessons from other countries may provide guidance regarding the timing and magnitude of the next COVID-19 wave of the pandemic in China. In this study, the COVID-19 surveillance data from 189 countries that experienced two or more waves of the SARS-CoV-2 Omicron variant were analysed. The median peak timing between the first and second/third waves of the SARS-CoV-2 Omicron variant was 164/243 days. The peaks of the second and third waves were much lower than that of the first wave. The median relative peaks of the second and third compared with the first waves were 14.5% and 11.2%, respectively. The time window between the peak timings of the first and second waves showed no significant rank correlation with the five socioeconomic factors included in this study. However, the relative peak of the second wave increased significantly with gross domestic product per capita (P<0.001), urbanisation rate (P=0.003), population density (P=0.007), and proportion of older adults >65 years (P<0.001), although decreased significantly with the proportion of 0-14 teenagers (P<0.001). In summary, the historical situations and progression of COVID-19 outbreaks in other countries may inform the risk assessment of incoming outbreaks in mainland China; however, the timing and magnitude of the next COVID-19 wave may also be influenced by several unknown factors, including rapid viral evaluation of SARS-CoV-2

The Omicron SARS-CoV-2 variant has become the dominant lineage worldwide, and experimental study had shown that SARS-CoV-2 Omicron variant was more stable on various environmental surfaces than ancestral strain. However, how the changes of stability on surfaces would influence the role of fomite route in SARS-CoV-2 transmission is still unknown. In this study, we modeled the Omicron and ancestral strain SARS-CoV-2 transmission within a household over 1-day period from multiple pathways, i.e., airborne, droplet and contact route. We assumed there were 2 adults and 1 child in the household, and one of the adults was infected with SARS-CoV-2. We assume a scenario of pre-/asymptomatic infection, i.e., SARS-CoV-2 was emitted by breathing and talking, and symptomatic infection, i.e., SARS-CoV-2 was emitted by breathing, talking, and coughing. In pre-/asymptomatic infection, all three routes contributed a role, contact route contribute most (37%-45%), followed by airborne route (34%-38%) and droplet route (21%-28%). In symptomatic infection, droplet route was the dominant pathway (48%-71%), followed by contact route (25%-42%), airborne route played a negligible role (<10%). In the contact route, indirect contact (fomite) route dominated (contributed more than 97%). Compared with ancestral strain, though the contribution of contact route increased in Omicron variant transmission, the increase was slight, from 25%-41% to 30%-45%.