sharon sanders
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- Published: 01 July 2023
Nature Communications volume 14, Article number: 3888 (2023) Cite this article
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In late 2022, China transitioned from a strict ‘zero-COVID’ policy to rapidly abandoning nearly all interventions and data reporting. This raised great concern about the presumably-rapid but unreported spread of the SARS-CoV-2 Omicron variant in a very large population of very low pre-existing immunity. By modeling a combination of case count and survey data, we show that Omicron spread extremely rapidly, at a rate of 0.42/day (95% credibility interval: [0.35, 0.51]/day), translating to an epidemic doubling time of 1.6 days ([1.6, 2.0] days) after the full exit from zero-COVID on Dec. 7, 2022. Consequently, we estimate that the vast majority of the population (97% [95%, 99%], sensitivity analysis lower limit of 90%) was infected during December, with the nation-wide epidemic peaking on Dec. 23. Overall, our results highlight the extremely high transmissibility of the variant and the importance of proper design of intervention exit strategies to avoid large infection waves.
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Discussion
We modeled the epidemic dynamics of the Omicron variant of SARS-CoV-2 in China from Nov. to Dec. 2022, during a period when China moved from having strict COVID-19 policies (‘zero-COVID’), to little-to-no intervention efforts. We found that after full exit from zero-COVID, the Omicron variant spread at a very high rate of 0.42/day, with a doubling time of 1.6 days, during early and mid-Dec. before the incidence peaked around Dec. 23. Our point estimate is that 97% of the population (1.4 billion people) was infected during December, with a lower 95% credibility interval of 95% of the population (1.33 billion) and a lower limit in the sensitivity analyses of 90% (1.26 billion). With an infection fatality ratio between 0.1 and 0.2% for the Omicron variant[SUP]19[/SUP], we would expect between 1.3 and 2.6 million COVID-19 deaths in China during Dec. 2022 as well as Jan. 2023 (because of the delay from infection to death).
Infection of more than one billion people during one month would lead to a large number of people needing health care, far exceeding the hospital capacity, and thus explains the report that hospitals were overwhelmed during this period[SUP]6[/SUP]. This outcome emphasizes the need for gradually relaxing intervention efforts (instead of abruptly changing policy) and implementing additional measures (e.g., pharmaceutical strategies) to ‘flatten the curve’[SUP]9[/SUP]. A slower epidemic wave would help to ease hospital burden, allow sufficient health care for infected people, prevent epidemic overshoot (i.e., a large final epidemic size because of rapid spread[SUP]20[/SUP]), and ultimately reduce the number of deaths. Such considerations may be of renewed importance later in 2023, when the large cohort of people infected at the end of 2022 may become susceptible to reinfection.
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